"...'...'.....'..'''''''.'.'.'.:'':''.'.'.'.'.'.~~~~"'::~" "'....'..''''''''''.'.'"""''''''''''~.'.'."'"'''"'."'...'''''''''''''''''''. '''''''''''.'::::::::::' .....~.~.''.= '....'....''''.'.'.'.' ''''''''':.:..''' ~ ...... '''' ..',.'.. '.'''''.... ''' '':'I'~'~'~''' ~.~.~ " ''~~~~~~~~~~~~~.~.~.~~ '"."'"'.'.'.'......'. '... ."...''''''' '' '. ...''.'::::::~:::::::: ''''''.'.'. .. ''::...'.. ''. '.. '. '.'.'.' .''''''''''.'' " . ... " ...... :: '.' ~~~~~~~~~ '... .... '.. '. ... '''''''

°

AGRICULTURAL of the ALABAMA
E. V. Smith, Director

EXPERIMENT POLYTECHNIC

STATION INSTITUTE
Auburn, Alabama,

CONTENTS
Page
PROCEDURE -

6--------

PRECIPITATION AND EVAPOTRANSPIRATION-13 OCCURRENCE OF DROUGHT-DAYS--

13

Number per Season -------Number per Month --------Number per 10-Day

-

-13 -16
16

Period -------------------------

AMOUNT OF WATER REQUIRED FOR IRRIGATION -----------EXCESS OF PRECIPITATION

17

------------------------------ 24

APPLICATION OF DATA---------------------------------25 SUMMARY AND CONCLUSIONS----------------------------30

LITERATURE

CITED ------------------------------------

32
---- - -- - - - - 3 4

A P PE NDIX - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - -

FIRST

PRINTING 5M,

SEPTEMBER

1959

ERRATA
Errors occurring in Alabama Experiment Station Bulletin No. 316, "Agricultural Drought in Alabama," are herewith corrected. Correction 1. The right hand total column, Table 5 page 24, is corrected to year and the data in this column are likewise revised. Correction 2. The next to last sentence, first paragraph page 25, is corrected to read as follows: In 5 out of 10 years, the annual excess in Alabama is 21 to 28 inches, except in the Gulf Coast area where the value is 34 inches. This same correction also applies to the second sentence, top of

page 31.
Correction 3. The last sentence, first paragraph page 25, should read: In 1 out of 10 years, the annual excess in most areas is 30 to 40 inches of precipitation.
TABLE 5. MONTHLY AND YEARLY EXCESS PRECIPITATION IN INCHES FOR 2-INCH BASE AMOUNT AND 4 PROBABILITIES BY DROUGHT AREAS

Area Prob. A 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 8/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10

B

C

D

E

F

G

H

I

J In. 10.1 8.2 6.8 4.3 10.5 8.1 6.1 4.2 9.8 7.8 5.8 3.8 8.5 5.2 3.6 2.5 7.0 4.7 3.7 2.6 6.0 4.5 3.7 2.8 7.9 5.2 4.1 2.8 5.7 4.4 3.6 2.4 6.9 4.9 3.9 2.3

F In. 8.9 7.2 5.9 3.1 9.2 6.7 5.3 3.6 7.7 6.7 5.9 3.7 6.8 5.4 4.4 2.8 6.2 4.8 4.1 2.8 5.5 4.3 3.5 2.3 6.5 5.0 3.8 2.5 6.3 5.0 3.9 2.2 6.4 4.4 3.3 1.9

M In. 6.3 5.3 4.6 .3.5 7.0 5.8 4.9 3.8 7.3 6.0 5.1 3.8 7.0 5.5 4.3 2.8 7.7 5.7 4.5 3.0 8.8 7.2 6.1 4.2 9.1 7.0 5.7 3.5 8.0 6.1 4.6 2.7 9.9 6.8 5.0 2.9

A In. 3.9 2.4 1.9 1.4 4.3 3.0 2.3 1.5 4.6 3.5 2.7 1.5 6.4 4.0 2.1 0.9 6.3 4.1 2.5 ,0.9 6.6 4.5 3.2 1.5 5.9 4.4 3.5 1.7 5.5 4.0 3.0 1.4 8.7 5.3 3.6 1.9

M In. 2.5 1.5 0.7 0.0 2.7 1.6 0.8 0.0 2.9 1.4 0.8 0.3 2.8 1.7 1.0 0.2 2.3 1.3 0.6 0.0 4.8 3.3 2.2 0.5 4.1 2.7 1.6 0.0 3.0 1.5 0.7 0.0 5.6 3.3 2.1 0.9

J In. 1.9 0.9 0.1 0.0 2.1 1.0 0.1 0.0 .1.7 1.1 0.3 0.0 1.4 0.7 0.3 0.0 1.9 1.0 0.3 0.0 4.4 2.3 1.0 0.0 2.4 1.3 0.5 0.0 2.3 1.0 0.0

J In. 2.8 1.9 1.2 0.1 4.3 2.8
,1.7

10.0

7.5 5.0 ,3.3 1.3

0.0 4.0 2.4 1.9 0.3 4.2 2.5 1.5 0.4 4.3 2.4 1.4 0.4 8.6 5.7 3.7 1.6 7.3 5.6 4.0 1.6 5.3 3.7 2.7 1.2 12.7 9.1 6.1 3.3

S In. 1.6 0.7 0.0 0.0 2.3 2.4 1.6 1.6 1.0 0.7 0.0 0.0 3.5 2.4 2.4 1.1 1.8 0.2 0.4 0.0 2.9 1.9 1.6 0.9 1.0 0.3 0.2 0.0 3.1 ,.3 1.8 1.2 1.0 0.7 0.0 0.0 3.4 6.0 1.9 3.8 1.2 2.3 0.3 0.8 5.2 4.8 3.4 2.9 2.4 1.7 1.0 0.3 4.5 3.8 ;3.2 2.3 2.4 1.5 0.3 8.8 7.3 4.7 5.7 3.3 4.4 1.8 5.5

A In. 2.2 1.1 0.9 0.0

11.2

O N In. In. 2.0 4.6 0.0 3.3 0.0 2.3 0.0 1.1 3.0 4.5 1.0 3.2 0.1 2.3 0.0 0.9 2.8 4.4 0.9 2.9 0.0 2.0 0.0 0.6 1.4 4.5 0.0 2.2 0.0 1.3 0.0 0.0 1.6 3.3 0.7 1.6 0.0 0.8 0.0 0.0 2.9 4.8 1.2 2.5 0.2 1.6 0.0 0.0 2.1 6.4 0.1 3.7 0.0 2.0 0.0 0.0 1.0 5.0 0.0 2.4 0.0 0.7 0.0 0.0 5.0 6.0 2.8 2.1 0.0 1.1 0.0 0.4

D Year In. In. 8.4 36 6.2 31 4.7 27 2.8 22 39 9.3 6.4 34 30 5.2 3.5 24 8.9 37 32 6.6 30 5.0 3.3 26 32 7.8 5.9 29 4.6 26 2.8 21 32 7.4 29 5.9 4.8 26 21 2.7 40 7.7 35 6.1 33 5.0 3.2 28 43 7.2 5.1 37 33 4.0 2.4 27 6.4 37 4.8 31 3.8 27 2.3 21 51 6.7 4.9 45 4.0 41 34 2.8

AGRICULTURAL EXPERIMENT STATION AUBURN UNIVERSITY

E. V. Smith, Director Auburn, Alabama

AGRICULTURAL DROUGI-IT
HENRY S. WARD, Botanist** C. H. M. VAN BAVEL, Principal Soil Scientist, U.S.D.A. J. T. COPE, JR., Associate Agronomist
L. M. WARE, Head, Department of Horticulture HERMAN BOUWER, Associate Agricultural Engineer* * *

PLANTS

use enormous quantities of water that are absorbed from the soil. An acre of corn may require 16 inches or 500,000 gallons of water during a growing season. This 16 inches of water is equivalent to approximately 1,618 tons. Of this amount, 1,600 tons are returned to the atmosphere. The other 18 tons, or 1.1 per cent, of water is used by the acre of corn plants for chemical combination and cell hydration, which are essential for growth and development of optimum yield. The water from which this 1.1 per cent is to be obtained must be continuously supplied during the growing season for normal growth and development. However, a supply of this water in plants is maintained only if sufficient water is available from the soil for transpiration. When transpiration exceeds water absorption, a deficit of water results in decreased transpiration and rate of growth. The water used by plants is absorbed from the soil moisture reservoir. The water in the soil moisture reservoir that is utilizable by plants is designated as available soil moisture. The available soil moisture is that held by the soil between field capacity (upper limit) and the permanent wilting percentage (lower level). Field capacity is the moisture percentage of a soil, expressed on a dry-weight basis, in the field 2 or 3 days after a thorough wet* A joint contribution of the Agricultural Experiment Station of The Alabama Polytechnic Institute and the Soil and Water Conservation Research Division, Agricultural Research Service, U.S. Department of Agriculture.
**

Resigned.

** The authors acknowledge with gratitude the cooperation of the National Weather Records Center, U.S. Weather Bureau, Asheville, N.C. in tabulating the records that served as the basis for this publication. Acknowledgement is also due E. F. Schultz, Jr., former Biometrician; Arthur R. Long, State Climatologist, U.S. Weather Bureau, Montgomery, Alabama, for helpful suggestions during the early phases of the study; and to F. D. Whisler, Soil Scientist, U.S. Department of Agriculture, for final summarization of the data.

4

ALABAMA AGRICULTURAL EXPERIMENT STATION

ting of the soil profile by rain or irrigation water. Permanent wilting percentage is the moisture percentage of soil at which plants wilt and fail to recover turgidity. The amount of available soil moisture is dependent on the size and arrangement of the soil pores. Fine-textured soils will hold more available water than coarse soils. The available moisture varies from as little as 0.2 inch per foot in some sandy soils to as much as 3.0 inches in some loams and clays. Thus, it is apparent that plants use large amounts of water by transpiration and the source of this water is the available moisture in soils. The supply in soils is absorbed into the plants at the tips of the root. The depth of root penetration determines how much of the soil reservoir is utilized for available moisture. The root zone is determined by physical, chemical, and biological properties of soils and by the kind of plant cover. The root zones of the various kinds of plant covers (crops, forest trees, etc.) that grow in the various soil types of Alabama are not accurately known. However, an estimate can be made of root occupancy in similar soil types on the basis of studies in other Southeastern States (2,3,5,6,7,8,10,12). A summary of this information is given in Table 1. The data on root occupancy in Table 1 show the root zones for only a few of the soil types in Alabama. In general, the plants have most of their roots distributed in the upper 12 inches of soil. Thus, the principal soil moisture reservoir is the top foot of soil. Water is lost to air from the soil either by direct evaporation from the soil surface or by transpiration from plants. The sum of transpiration and evaporation is designated by the term evapotranspiration. Evapotranspiration occurs when water is available, energy is available to convert water to vapor, and the atmosphere as a whole has a saturation deficit. Van Bavel (14) points out that several investigators showed that various kinds of plant covers do not differ materially in their evapotranspiration rates. If water is available, the rate of evapotranspiration appears to be controlled by climatic conditions. Aslying (1) and Lull (9) in their extensive reviews of evapotranspiration studies concluded that, by using daily calculated evapotranspiration rates, the rate of movement of water from the soil reservoir can be accurately determined. As long as available soil moisture is present in the root zone, evapotranspiration occurs and the water requirements of the plant cover are met without serious drought damage. However,

AGRICULTURAL DROUGHT in ALABAMA

5

TABLE 1. ROOT OCCUPANCY OF SEVERAL KINDS OF PLANTS IN VARIOUS SOIL TYPES

Kind of plant

Type of soil

Principal zone Depth of root growth of root occupancy Inches Inches
18
0 to

Cotton ------------------------ arlboro sandy loam M 16 Peanuts ----------------------Norfolk sandy loam 24 Alfalfa ---------------------- Norfolk sandy loam 48 Alfalfa .-----------------------------Cecil clay loam 72 Bermudagrass Norfolk sandy loam 35 Carpetgrass-------------------- sandy loam Norfolk 30 St. Augustine-grass -----------Norfolk sandy loam 35 Centipedegrass-----------------Norfolk sandy loam 33
Bahiagrass-

Corn ----------------------Norfolk sandy loam Corn ________________________ clay loam ______ecil

14

18

0 to 14
0 to 8 0 to 14 0 to 6 0 to 12

--------------------

0 to 0 to
0 to

8 8
8

-----------sandy loam ______---Norfolk 35 Peach (Mikado) _______________Cecil clay loam 52 Tung tree ------------------------Ruston sandy loam 34

0 to
0 to 0 to

8
8 6

0 to 18
0 0 0 0 to to to to 6 5 8 9

Longleaf pine ------------------ 32 Ruston sandy loam Loblolly pine Alamance clay loam 37 Shortleaf pine Alamance sandy loam 38 Red Oak----------------------------Georgeville clay loam 36 Sweetgum -------------------------Congaree sandy loam 49 Yellow poplar ------------------- 49 Congaree sandy loam

--------------------------------------

0 to 19 0 to 19

when the available soil moisture is depleted, crops are in danger of drought damage unless the available soil moisture is replaced either by rainfall or irrigation. Van Bavel (14) defines agricultural drought as a condition in which there is insufficient soil moisture available to a crop. Agricultural drought probably occurs every year in Alabama, and with modern fertilizer practices these water deficits are the principal cause of failure to obtain maximum yields. Realization of agricultural drought has resulted in much interest in irrigation in Alabama and the other states east of the Mississippi River. Irrigated acreage in 31 states of the humid region was 70 per cent greater in 1954 than in 1949, according to the 1954 Census of Agriculture. The present study was made of agricultural drought in Alabama by using the procedure of Van Bavel (14). Similar studies have been completed for North Carolina, Virginia, South Carolina, and Georgia (15,16,17,18). The objectives of this study were: 1. To determine probable occurrence of drought conditions. 2. To evaluate need for irrigation and irrigation research. 3. To aid in establishment of general water policies for agriculture, industry, and municipalities. 4. To determine excess water and its relation to drainage, conservation, and flood control.

6

ALABAMA AGRICULTURAL

EXPERIMENT STATION

PROCEDURE

The methods for estimating drought occurrence are those of Van Bavel, and are given in detail in the North Carolina agricultural drought publication (15). In brief, the method consists of combining existing data on daily rainfall with estimates of daily water losses through evapotranspiration and determining the number of times that available moisture in the soil is reduced to zero. A day when available moisture is zero is called a drought-day. Thornthwaite and Mather (11) have proposed a similar method of determining when to irrigate. The estimation of soil moisture conditions from climatological data is determined by five distinct steps. These are the procureTABLE 2. LIST OF 27 RAINFALL STATIONS USED IN COMPUTATION OF

DROUGHT INCIDENCE IN ALABAMA

Area and station

County

Number as given in
Figures 1 and 2

Limestone Valleys, Appalachian Plateau, and Piedmont Areas Area A: Area B: Decatur Muscle Shoals Guntersville Madison Scottsboro Anniston Birmingham Gadsden Saint Bernard Morgan Colbert Marshall Madison Jackson Calhoun Jefferson Etowah Cullman 7 18 13 15 24 1 3 10 23

Area C:

Black Belt and Coastal Plain Areas Area D: Dancy Greensboro Pushmataha Selma Thomasville Auburn Clanton Montgomery Jackson Lock I Mobile Brewton Greenville Riverfalls Dothan Eufaula Ozark Troy Robertsdale Pickens Hale Choctaw Dallas Clarke Lee Chilton Montgomery Clarke Mobile Escambia Butler Covington Houston Barbour Dale Pike Baldwin 6 11 20 25 26 2 5 17 14 16 4 12 21 8 9 19 27 22

Area E:

Area F: Area G:

Area H:

Area I:

AGRICULTURAL DROUGHT in ALABAMA

7

ment of rainfall data, estimation of evapotranspiration, estimation of moisture storage capacity of the soil, computation of daily soil moisture balance, and classification of data. The daily precipitation data were taken from official United States Weather Bureau records, as furnished by the National Records Center in Asheville, North Carolina. The records of 27 stations in Alabama for a period of 25 years, 1930-1954, were used. These data were entered upon punch cards, together with any available data on maximum and minimum temperatures. The cards are stored by the Agricultural Experiment Station of The Alabama Polytechnic Institute, Auburn. The list of stations is given in Table 2 and their location is shown in Figures 1 and 2. Estimated values for daily evapotranspiration were obtained with the formula proposed by Penman, and its use is discussed in detail by Van Bavel (15). The formula gives maximum evapotranspiration from a large homogeneous plant cover of maximum occupancy and with ample available soil moisture. To use the Penman equation, one requires weather data on sunshine duration, air temperature, relative humidity, and windspeed. These data have been measured in Alabama at only four stations, namely Anniston, Birmingham, Montgomery, and Mobile. To offset the lack of data in Alabama, stations were taken in adjacent states. Stations in Georgia were Atlanta, Macon, and Thomasville, while other stations were Jackson, Mississippi, Pensacola, Florida, and Chattanooga, Tennessee. After an examination of the average daily evapotranspiration for each month for all of the stations, Alabama was divided into two areas. The northern area evapotranspiration values were averages of Chattanooga, Atlanta, Anniston, and Birmingham, whereas the southern area evapotranspiration values were averages of Macon, Thomasville, Jackson, Pensacola, Mobile, and Montgomery. The division of Alabama into two evapotranspiration areas is shown in Figure 1. Average daily evapotranspiration, and totals for each month and area are given in Table 3. Monthly averages for each year during the 25-year period are in Appendix Tables 1 and 2. In order to compute the daily balance of available soil moisture, the maximum storage capacity in the root zone must be estimated. As previously pointed out, the maximum storage capacity depends upon the field capacity, depth of the root zone, and soil moisture content at the lower limit of availability. The value may vary from less than 1 to several inches, depending

8

ALABAMA AGRICULTURAL EXPERIMENT STATION

FIGURE 1. The northern and southern areas for evapotranspiration, with location of precipitation stations in Alabama.

AGRICULTURAL DROUGHT in ALABAMA

9

FIGURE 2. Areas used for monthly and 10-day-period drought probabilities, excess moisture, and irrigation requirements, with location of precipitation stations in Alabama.

10

10 ALABAMA AGRICULTURAL EXPERIMENT STATION
TABLE 3. AVERAGE MONTHLY EVAPOTRANSPIBATION FOR NORTHERN AND SOUTHERN AREAS OF ALABAMA, 1930-1956 Month Northern area Southern area

In/day In/mo. In./day In/mo. January--------------------------------.026 .81 .041 1.27 February-------------------------------.048 1.34 ..066 1.85 2 .67 .067 2.08 .086 M arch ------------------------------------------ -------------------April----------------------------------.107 3.21 .130 3.90 May------------------------------------.142 4.40 .160 4.96 June-----------------------------------.173 5.19 .185 5.55 5.02 .162 4.77 .154 July-----------------------------------August ----------------------------------------

September-----------------December
------------------------------

----

.141 .120

4.37

October--------------------------------November-------------- --TOTAL PER YEAR----------------------

.080

.043

3.60 2.48
1.29

.158 .134
.100
.060

4.90

4.02 3.10
1.80

.024

.74
34.28

.038

1.18
40.22

upon the value of the foregoing 3 factors. Therefore, the maximum amount of water that a soil can hold and make available to a crop was used as a variable in this study. The amounts used were 1, 2, 3, and 5 inches. By computing the drought-days for each of these values, the results may be used to cover most soil conditions. The number of drought-days was determined by computation of the daily soil moisture balance. It was assumed that the amount of water in the root zone is at its maximum value at the beginning of the year, January 1. From then on, on each day a new balance was computed by adding any rainfall that occurred and subtracting the estimated amount of evapotranspiration. This procedure was followed for the 27 stations in the State for each of the 25 years. Average daily evapotranspiration values used for each month were those for the year involved, as given in Appendix Tables 1 and 2. The daily soil moisture balance estimates were subject to two conditions. First, by cancelling any occurring excess, the daily balance was not allowed to exceed the base amounts, i.e., 1, 2, 3, and 5 inches; and second, by cancelling any amount below zero, the balance was not allowed to become negative. Incidence of zero or negative amounts marks the occurrence of a drought-day and the total number is recorded for each day, and the total number is recorded for each month and 10-day period within
a month. No account is taken of

surface runoff

and the depen-

dence of evapotranspiration upon soil moisture content. These computations are approximations of what happens under field

AGRICULTURAL

DROUGHT

in

ALABAMA

11

conditions, but the errors involved are not sufficiently large to affect results appreciably. A more detailed discussion is given by Van Bavel (15). The calculation as outlined was done for each of the four basic amounts by using electronic computers and related equipment. The procedure involved use of a single punch card for each day, upon which were recorded the daily rainfall, pertinent value of evapotranspiration, and results of the calculation for the four soil storage values. Tabulations were prepared from the punch cards by printing the monthly moisture excess, monthly total of drought-days, and 10-day total of drought-days for each month of record and for each station. Annual totals of each characteristic were also obtained. From the machine tabulations, frequency distributions were computed of the total number of drought-days during March through November and the annual value of excess moisture of each of the 27 stations in Alabama. These frequency curves were interpolated at probability levels of 1, 2, 3, and 5 out of 10 to yield the minimum number of drought-days for each station and each of the 4 base amounts. The data were then plotted on a map of Alabama and lines of equal drought incidence drawn. Frequency curves were made for monthly and 10-day totals of drought-days for each base amount. However, these were based upon the aggregated data of several stations. For this purpose the state of Alabama was divided into nine areas, within which monthly drought probabilities were similar. These 9 areas are outlined in Figure 2. For each area, therefore, a set of frequency curves was prepared and these were interpolated at probabilities 1, 2, 3, and 5 out of 10. A similar procedure was followed for the monthly totals of excess precipitation. The inches of irrigation water required to prevent occurrence of drought-days was obtained by taking the expected minimum number of drought-days for each month and each area at odds of 1 out of 10 and multiplying this amount by the estimated daily evapotranspiration. These figures represent an amount of water that will exceed the demand in 9 out of 10 years and will be short of the demand only in the remaining year. Irrigation requirements applying to odds of 7 out of 10 years and 5 out of 10 years were computed in a similar manner.

12

ALABAMA AGRICULTURAL

EXPERIMENT

STATION

-C 0

E

CL

0) -C

FIGURE 3. Monthly precipitation and monthly evapotranspiration at four stations in Alabama.

AGRICULTURAL

DROUGHT

in

ALABAMA

13

PRECIPITATION and EVAPOTRANSPIRATION A qualitative picture of the sufficiency of rainfall for crop production in Alabama can be obtained by comparing average values of monthly rainfall with average values of monthly evapotranspiration. This is illustrated by the data shown in Figure 3 for the four stations, Anniston, Birmingham, Montgomery, and Mobile. With the exception of Mobile, average evapotranspiration is higher than average rainfall during May, June, and September. The graphs indicate definite shortages of soil moisture or droughts during the summer months and an excess during the winter. Summer drought is particularly pronounced at Montgomery. OCCURRENCE of DROUGHT-DAYS Number per Season Each of the 27 stations had frequency distributions prepared of the total number of drought-days during the months of March through November. These are not all presented but, instead, 9 stations were selected, one for each of the areas indicated in Figure 2. The frequency distributions are shown in Appendix Figures 1 through 9. On the horizontal axis, these graphs show the minimum number of drought-days and on the vertical axis the associated value of the probability expressed in per cent. A reasonably fitting straight line could be drawn through the points without much difficulty. The lines were fitted by eye. Separate lines are shown for each of the four base amounts of soil moisture. The effect of the storage capacity of soils for available water upon drought incidence is apparent from the data in Appendix Figures 1 through 9. Often an increase of 1 inch in storage capacity means a decrease of 50 per cent in the chances for a similar drought occurrence. To facilitate use of information concerning the expected number of drought-days per season, it is presented in the form of maps rather than graphs, Figures 4 through 7. These maps show the minimum number of drought-days expected for the period March through November at four probability levels and at the base amounts of 1 and 2 inches of available root zone moisture. Maps for the 3- and 5-inch base amounts are not presented. Research information available at present by Cooper et al. (4)

14

ALABAMA AGRICULTURAL EXPERIMENT

STATION

FIGURE 4. Probability of 1 and 2 out of 10 years for the minimum number of drought-days to occur in the period of March through November for 1 inch of soil moisture capacity.

FIGURE 5. Probability of 3 and 5 out of 10 years for the minimum number of drought-days to occur in the period of March through November for 1 inch of soil moisture capacity.

AGRICULTURAL

AGRICLTUR~Lb ~

DROUGHT

in

ALABAMA

15

DblRUGH

in AL ABAMlA1

FIGURE Probability of 1 and 2 out of 10 years for the minimum number of drought-days to occur in the period of March through November for 2 inches of soil moisture capacity.

6.

800f-

70I

60

80

70

60

FIGURE 7. Probability of 3 and 5 out of 10 years for the minimum number of drought-days to occur in the period of March through November for 2 inches of soil moisture capacity.

16

ALABAMA AGRICULTURAL EXPERIMENT STATION

indicates that most soils in Alabama do not hold more than 1 and 2 inches of available moisture in the root zone of crop plants. In interpreting the state maps, Figure 4, for example, shows that for a soil storage capacity of 1 inch of available water in central and southeastern Alabama there will be at least 140 drought-days in 1 out of 10 years. Under the same conditions in northern Alabama, there will be between 120 and 130 droughtdays. From Figure 5, the corresponding values to be expected in 5 out of 10 years, or every other year, are 110 days in the central and southeastern sections and 90 to 100 days in the northern section.
Number per Month

For individual crops, an interpretation of data on a seasonal basis is too general. Therefore, the same procedure used for the entire season was used to determine the distribution of the number of drought-days for each month. In order to condense the information, Alabama was divided into nine areas as indicated in Figure 2. Data from all 27 stations were used with several stations combined for each area. The minimum number of drought-days for 4 base amounts of soil moisture storage capacity and 4 probabilities were prepared for each area and each of 9 months. The results are given in Appendix Table 3. In order to use this table, it is necessary to refer to Figure 2 for the key to the area designations. For example, the southeastern section of Alabama is designated as Area H. Appendix Table 3 shows that in 2 out of 10 years there will be 21 or more drought-days during June in that area if the maximum soil moisture storage capacity is 2 inches. The corresponding value for 5 out of 10 years is 14 drought-days.
Number per 10-Day Period

The same procedure that was followed for determining the number of drought-days for the entire season and for each month was used to obtain the number of drought-days for each 10-day period from March through November. Appendix Table 4, therefore, gives for the nine areas indicated in Figure 2 the minimum number of drought-days at four levels of probability and for the four base amounts of soil moisture.

AGRICULTURAL

DROUGHT

in

ALABAMA

17

The distribution of drought-days at 10-day intervals permits a better application of the data to crops. By combination of the proper 10-day intervals, the number of drought-days can be related to the growth period of a crop either for the entire period or for stages of growth particularly affected by water deficits. However, addition of 10-day interval drought-days does not give an exact estimate of the expected number of drought-days for a larger period. The addition of 10-day intervals over-estimates drought incidence, so that merely adding 10-day intervals results in "safe" values. The distribution of drought-days by 10-day periods for 5 out of 10 years when the available root zone soil moisture is 1 and 2 inches is plotted for each of 8 areas of Alabama in Figures 8 through 15. In general, the graphs show that drought occurrence is concentrated in May and June with noticeable declines in July and the first 10 days of August. Drought is severe in October in areas, D, E, F, G, and H (southern Alabama), whereas lower drought incidence occurs in October in areas A, B, and C (northern Alabama). AMOUNT of WATER REQUIRED for IRRIGATION By multiplying the expected number of drought-days in a month as given in Appendix Table 3 by the average daily evapotranspiration data of Table 3, the amount of water needed for irrigation can be computed. These irrigation water requirements for the nine different areas of the State are given in Table 4. This table lists for the 4 base amounts of soil moisture for each month the quantities of water required that will not be exceeded in 9 out of 10 years. Use of these data assumes that the water is applied to the land without any waste and all soil moisture deficiency is eliminated. However, in estimating actual water requirements, some allowance, about 30 per cent, should be added to compensate for distribution and application losses. In determining water storage requirements for irrigation, estimated seepage and evaporation losses must be added to the quantities of water required for irrigation. The monthly irrigation requirements by areas and base amounts can be computed for the other probabilities by multiplying the drought-days shown in Appendix Table 3 by the average monthly evapotranspiration presented in Table 3.

18

ALABAMA AGRICULTURAL

EXPERIMENT STATION

Drought days per
10- day period

8
7 $1" Base amount

6
5

1
\

4 2MBase amount
3 0 1

Mar.

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

FIGURE 8. Minimum number of drought-days to be expected in Area A for 1and 2-inch soil moisture capacities in 5 out of 10 years during 10-day periods from March through November.

Drought days per I0-day period

AREA B

8
SI"Bose

amount

0

Mar.

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

FIGURE 9. Minimum number of drought-days to be expected in Area B for 1and 2-inch soil moisture capacities in 5 out of 10 years during 10-day periods from March through November.

AGRICULTURAL

DROUGHT

in

ALABAMA

AGRICULTURAL

DROUGHT in ALABAMA

19 19

W

Mar.

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

FIGURE 10. Minimum number of drought-days to be expected in Area C for 1and 2-inch soil moisture capacities in 5 out of 10 years during 10-day periods from March through November.

Drought days per 10-day period

AREA D

Sl"Bse

amount

3l

1

r
Mar. Apr. May June July

/

2"Base amount

Aug.

Sept.

Oct.

Nov.

FIGURE 11. Minimum number of drought-days to be expected in Area D for 1and 2-inch soil moisture capacities in 5 out of 10 years during 10-day periods from March through November.

20

ALABAMA AGRICULTURAL EXPERIMENT

STATION

Drought days per 0I-day period 8

5

i

3I 1
Mar. Apr. May June July Aug.

I
2"Base amount
Sept. Oct. Nov.

FIGURE 12. Minimum number of drought-days to be expected in Area E for 1and 2-inch soil moisture capacities in 5 out of 10 years during 10-day periods from March through November.

9

Drought days per 10- day period

AREA F

8

6

-

I"Base amount

-

I \$2"Base amount

Mar.

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

FIGURE 13. Minimum number of drought-days to be expected in Area F for 1and 2-inch soil moisture capacities in 5 out of 10 years during 10-day periods from March through November.

AGRICULTURAL

ARICLTURA

DROUGHT

DROUGH

in

in ALABAMA21

ALABAMA

21

9 8 7 6 5 4 3 2

I O
Mar.
I

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

FIGURE 14. Minimum number of drought-days to be expected in Area G for 1and 2-inch soil moisture capacities in 5 out of 10 years during 10-day periods from March through November.

9

",-"

AREA H,

frm

arh

houh

ovmbr

Mar.

Apr.

May

June

k"/

July

Aug.

2"Base amount Sept. Oct. Nov.

FIGURE 15. Minimum number of drought-days to be expected in Area H for 1and 2-inch soil moisture capacities in 5 out of 10 years during 10-day periods from March through November.

TABLE 4.

MINIMUM

MONTHLY

IRRIGATION REQUIREMENTS IN 9 OUT OF 10 YEARS FOR 4 BASE AMOUNTS (AVERAGE FOR THE 25-YEAR PERIOD)

BY DROUGHT AREAS

Area A

Basis In. 1 2 3 5 1 2 3 5 1 2 3 5 1 2 3 5 1 2 3 5

Feb. In. 0 0 0 0 0 0 0 0 0 0 0 0 .40 0 0 0 .40 0 0 0

Mar. In. 0 0 0 0 0 0 0 0 0 0 0 0 .69 0 0 0 .60 0 0 0

Apr. In. 1.61 1.07 0 0 1.50 .54 0 0 1.50 .54 0 0 2.08 1.17 0 0 1.95 .91 0 0

May In. 3.55 3.12 2.27 .14 3.41 2.84 2.13 .57 3.41 2.98 1.99 .14 4.16 3.36 2.40 .80 4.00 3.36 3.04 1.12

June In. 4.67 4.67 4.32 3.81 4.32 4.15 3.98 3.29 4.32 4.32 4.32 2.94 4.81 4.62 4.26 3.52 4.62 4.62 4.44 8.88

July In. 3.54 3.54 3.39 3.23 3.70 3.54 3.54 3.08 3.54 3.39 3.08 2.62 3.56 3.24 3.08 3.08 3.56 3.24 3.24 2.92

Aug. In. 3.67 3.38 3.24 3.24 3.52 3.10 2.68 2.26 2.96 2.54 2.12 1.83 4.42 4.11 3.79 3.48 3.48 2.84 2.69 2.53

Sept. In. 3.00 2.88 2.88 2.64 3.12 2.88 2.76 2.40 3.00 2.88 2.64 2.28 3.35 3.35 3.22 2.81 3.48 3.35 3.22 2.81

Oct. In. 2.00 1.84 1.84 1.76 2.00 1.84 1.76 1.76 2.00 1.84 1.76 1.68 2.80 2.80 2.70 2.70 2.60 2.60 2.60 2.60

Nov. In. .34 .30 .30 .26 .39 .30 .30 .30 .52 .47 .39 .34 1.20 1.14 1.14 1.02 1.08 1.08 1.02 .96

Dec. In. 0 0 0 0 0 0 0 0 0 0 0 0 .15 .08 .08 .04 .15 .04 .04 .04 Continued
-I 0Z

B

w

C

C
C

D

M a Ix M ;
m

E

Z
-

C r-I TABLE 4 (CONT'D). MINIMUM

C
MONTHLY IRRIGATION REQUIREMENTS IN 9 OUT OF 10 YEARS FOR (AVERAGE FOR THE 25-YEAR PERIOD)

4

BASE AMOUNTS BY DROUGHT AREAS

Area F

Basis In. 1 2 3 5 1 2 3 5 1 2 3 5
I1

Feb. In. 0 0 0 0 0 0 0 0 .46 0 0 0 .59 0 0 0

Mar. In. .86 0 0 0 .69 0 0 0 .69 0 0 0 1.12 0 0 0

Apr. In. 2.08 1.17 0 0 2.08 1.17 0 0 2.21 1.30 0 0 2.73 1.82 0 0

May In. 4.16 3.52 2.88 .96 3.68 3.36 2.72 1.12 4.16 4.00 3.84 1.76 3.52 3.36 3.20 1.92

June In. 4.62 4.26 4.26 3.70 4.81 4.44 4.26 3.52 4.62 4.44 4.44 3.88 4.26 4.07 3.70 2.40

July In. 3.40 3.24 3..08 2.43 3.08 2.75 2.75 2.43 3.08 2.59 2.59 2.43 2.11 1.78 1.78 1.13

Aug. In. 3.16 2.37 1.90 1.58 3.00 2.37 1.90 1.26 3.00 2.87 1.74 1.58 2.69 1.74 1.11 .95

Sept. In. 3.21 2.81 2.81 2.14 2.95 2.68 2.28 1.47 3.62 3.48 3.22 2.14 3.08 2.28 1.88 .27

Oct. In. 2.80 2.70 2.70 2.60 2.80 2.50 2.50 2.20 2.80 2.70 2.60 2.40 2.60 2.20 1.90 1.40

Nov. In. 1.26 1.02 .96 .48 1.26 1.20 1.20 .96 1.38 1.32 1.32 1.26 1.08 1.02 .90 0

Dec. In. .23 .12 .12 .08 .30 .23 .23 .15 .38 .23 .23 .08 0 0 0 0

C

O

0 -I -.
I-

G

H

2 3 5

iw

24

ALABAMA

AGRICULTURAL

EXPERIMENT

STATION

EXCESS of PRECIPITATION

Excess precipitation as used here means all rainfall that occurs after the soil has attained field capacity. This excess is disposed of by surface runoff and deep percolation. The relative magnitude of runoff and percolation for a given watershed depends on watershed infiltration characteristics and on the distribution of the rainfall occurrences and intensity.
TABLE 5. MONTHLY AND TOTAL ANNUAL EXCESS PRECIPITATION IN INCHES FOR 2-INCH BASE AMOUNT AND 4 PROBABILITIES BY DROUGHT AREAS

Area Prob. A

J In.

F In. 8.9 7.2 5.9 3.1 9.2 6.7 5.3 3.6 7.7 6.7 5.9 3.7 6.8 5.4 4.4 2.8 6.2 4.8 4.1 2.8 5.5 4.3 3.5 2.3 6.5 5.0 3.8 2.5 6.3 5.0 3.9 2.2 6.4 4.4 3.8 1.9

M In. 6.3 5.3 4.6 3.5 7.0 5.8 4.9 3.8 7.3 6.0 5.1 3.8 7.0 5.5 4.3 2.8 7.7 5.7 4.5 3.0 8.8 7.2 6.1 4.2 9.1 7.0 5.7 3.5 8.0 6.1 4.6 2.7 9.9 6.8 5.0 2.9

A In. 3.9 2.4 1.9 1.4 4.3 3.0 2.3 1.5 4.6 3.5 2.7 1.5 6.4 4.0 2.1 0.9 6.3 4.1 2.5 0.9 6.6 4.5 3.2 1.5 5.9 4.4 3.5 1.7 5.5 4.0 3.0 1.4 8.7 5.3 3.6 1.9

M In. 2.5 1.5 0.7 0.0 2.7 1.6 0.8 0.0 2.9 1.4 0.8 0.3 2.8 1.7 1.0 0.2 2.3 1.3 0.6 0.0 4.8 3.3 2.2 0.5 4.1 2.7 1.6 0.0 3.0 1.5 0.7 0.0 5.6 3.3 2.1 0.9

J In. 1.9 0.9 0.1 0.0 2.1 1.0 0.1 0.0 1.7 1.1 0.3 0.0 1.4 0.7 0.3 0.0 1.9 1.0 0.3 0.0 4.4 2.3 1.0 0.0 2.4 1.8 0.5 0.0 2.3 1.0 0.0 0.0

J In. 2.8 1.9 1.2 0.1 4.3 2.8 1.7 0.0 4.0 2.4 1.9 0.3 4.2 2.5 1.5 0.4 4.3 2.4 1.4 0.4 8.6 5.7 3.7 1.6 7.3 5.6 4.0 1.6 5.3 3.7 2.7 1.2

A In. 2.2 1.1 0.9 0.0 2.3 1.6 1.0 0.0 8.5 2.4 1.8 0.4 2.9 1.6 1.0 0.2 3.1 1.8 1.0 0.0 3.4 1.9 1.2 0.3 5.2 3.4 2.4 1.0 4.5 3.2 2.4 1.2 8.8 4.7 3.3 1.8

S In. 1.6 0.7 0.0 0.0 2.4 1.6 0.7 0.0 2.4 1.1 0.2 0.0 1.9 0.9 0.3 0.0 2.3 1.2 0.7 0.0 6.0 3.8 2.3 0.8 4.8 2.9 1.7 0.3 8.8 2.3 1.5 0.3 7.3 5.7 4.4 5.5

0 In. 2.0 0.0 0.0 0.0 8.0 1.0 0.1 0.0 2.8 0.9 0.0 0.0 1.4 0.0 0.0 0.0 1.6 0.7 0.0 0.0 2.9 1.2 0.2 0.0 2.1 0.1 0.0 0.0 1.0 0.0 0.0 0.0 5.0 2.8 0.0 0.0

D Total N In. In. In. 4.6 3.8 2.3 1.1 4.5 3.2 2.3 0.9 4.4 2.9 2.0 0.6 4.5 2.2 1.3 0.0 3.3 1.6 0.8 0.0 4.8 2.5 1.6 0.0 6.4 3.7 2.0 0.0 5.0 2.4 0.7 0.0 6.0 2.1 1.1 0.4 8.4 6.2 4.7 2.8 9.3 6.4 5.2 3.5 8.9 6.6 5.0 8.8 7.8 5.9 4.6 2.8 7.4 5.9 4.8 2.7 7.7 6.1 5.0 3.2 7.2 5.1 4.0 2.4 6.4 4.8 3.8 2.3 6.7 4.9 4.0 2.8 55.2 88.7 29.1 16.3 61.6 42.8 30.5 17.5 60.0 42.8 31.5 17.7 55.6 35.6 24.4 12.6 53.4 35.2 24.4 12.4 69.5 47.3 33.7 17.2 68.9 46.4 33.3 15.8 56.8 38.4 26.9 13.7 91.5 59.0 40.1 25.0

1/10 10.1 2/10 8.2 3/10 6.8 5/10 4.3 1/10 10.5 2/10 8.1 3/10 6.1 5/10 4.2 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 9.8 7.8 5.8 3.8 8.5 5.2 3.6 2.5 7.0 4.7 3.7 2.6 6.0 4.5 3.7 2.8 7.9 5.2 4.1 2.8 5.7 4.4 3.6 2.4 6.9 4.9 3.9 2.3

B

C

D

E

F

G

H

I

7.5 12.7 5.0 9.1 3.3 6.1 1.83 3.8

AGRICULTURAL

DROUGHT

in

ALABAMA

25

For each of the nine areas in Alabama, yearly totals and monthly totals of daily excess of precipitation were computed for four different base amounts of soil moisture and four different odds. These data show that the effect of the base amount of soil moisture upon the annual and monthly excess was small. Therefore, monthly excess of soil moisture or precipitation for the 2-inch base amount is presented in Table 5. These data, as do the drought-day graphs in Figures 8 through 15, clearly show that most of the excess precipitation in Alabama occurs during the period of December through March. In 5 out of 10 years, the annual excess in Alabama is 12 to 18 inches, except in the Gulf Coast area where the value is 25 inches. In 1 out of 10 years, the annual excess in most areas is 50 to 70 inches of precipitation. APPLICATION of DATA The usefulness to farmers of the data presented is dependent on proper application of the drought data to individual crops and soil types. The variations in moisture-holding capacity between soils makes an understanding of this characteristic of any soil necessary in determining its susceptibility to drought. The available moisture-holding capacity of soils is dependent on texture, structure, organic matter content, and depth of the plant root zone. It is measured in inches of water per foot of soil. Values taken from the Sprinkler Irrigation Guides for Alabama (13) for most of the commonly occurring soils in the State are presented in Table 6. Names of soil types at any location can be found in the county soil survey reports. The approximate available moisture-holding capacity per foot of soil can be determined from Table 6. In cases of soils not listed in this table, the information on other soils of similar texture and other moisture characteristics may be used. The principal zone of root occupancy varies between soils and between crops. Information on this characteristic of several crops and soils is presented in Table 1. For most soils and crops it varies from 1 to 2 feet. To determine the total available moisture that a soil will hold, the amount held per foot must be multiplied by the number of feet in the root zone. This figure may then be applied to information presented on drought to determine the probabilities of drought for this soil and location throughout the year.

26

ALABAMA AGRICULTURAL EXPERIMENT

STATION

A specific example is used here to demonstrate formation may be applied to any field in Alabama. ment Station Agronomy Farm at Auburn is used in The Lee County Soil Survey Report (19) identifies

how this inThe Experithis example. the soil as a

TABLE 6. CLASSIFICATION OF SOME SOILS OF THE GENERAL SOIL AREAS OF ALABAMA BY THEIR AVAILABLE MOISTURE-HOLDING CAPACITY IN INCHES PER FOOT

1.2 inches Baxter Cherty silt loam Fullerton Cherty silt loam Clarksville Cherty silt loam Minvale Cherty silt loam Pace Cherty silt loam

Limestone Valley Soils 1.6 inches Colbert silt loam Cumberland silt loam Decatur silt loam Dewey silt loam Dowellton silt loam Etowah silt loam Hermitage silt loam Hollywood silty loam Talbott silt loam Talbott silty clay loam

2.0 inches Abernathy silt loam Egam silty clay loam Humphreys silt loam Huntington silt loam Linside silty clay loam Lobelville silt loam Locust fine sandy loam Locust silt loam Melvin silt loam Prader silt loam Staser silt loam

Appalachian Plateau Sandstone Soils 2.0 inches 1.6 inches Enders fine sandy loam Allen fine sandy loam Atkins silt loam Waynesboro loam Hanceville fine sandy loam Hartsells fine sandy loam Holstun fine sandy loam Linker fine sandy loam Jefferson fine sandy loam Philo silt loam Pope silt loam Pope fine sandy loam Tillsit fine sandy loam Tillsit silt loam 1.2 inches Lloyd clay loam Davidson clay loam Piedmont Soils 1.3 inches Wickham sandy loam Altavista sandy loam Black Belt Soils 1.6 inches Octibbeha fine sandy loam Octibbeha clay loam Sumter clay Tuscumbia fine sandy loam Tuscumbia clay loam Vaiden fine sandy loam Vaiden clay loam Wilcox fine sandy loam Wilcox clay loam 2.0 inches Madison sandy loam Appling sandy loam Cecil sand loam 2.0 inches Catalpa clay loam Houston clay West Point (Bell) clay

Continued

AGRICULTURAL

DROUGHT

in

ALABAMA

27

TABLE 6 (CONT'D). CLASSIFICATION OF SOME SOILS OF THE GENERAL SOIL AREAS OF ALABAMA BY THEIR AVAILABLE MOISTURE-HOLDING CAPACITY IN INCHES PER FOOT

0.7 inches Americus (Red Bay) loamy sand Amite loamy sand Eustis (Ruston) loamy sand Huckabee (Kalmia) loamy sand Independence (Cahaba) loamy sand Lakeland (Norfolk) loamy sand Orangeburg loamy sand Scranton loamy sand

Coastal Plain Soils 1.0 to 1.2 inches Akron sandy loam Atwood sandy loam Cahaba sandy loam Carnegie sandy loam Faceville sandy loam Greenville sandy clay Kalmia sandy loam Lynchburg sandy loam Magnolia sandy loam Norfolk sandy loam Ora sandy loam Orangeburg sandy loam Prentiss sandy loam Red Bay sandy loam Ruston sandy loam Savannah sandy loam Shubuta sandy loam Tilden sandy loam

1.3 to 1.6 inches Bladen sandy loam Chewacla sandy loam Congaree sandy loam Coxville sandy loam Dunbar sandy loam Irvington sandy loam Yuka sandy loam Marlboro sandy loam Ocklockonee sandy loam Tifton sandy loam Unnamed soil (potato

land)

--

Chesterfield fine sandy loam. From Figure 16 it is determined that Auburn is in the Coastal Plain. Although the Coastal Plain soils listed in Table 6 do not include Chesterfield, its moisture characteristics are known to be similar to those of Norfolk, Magnolia, and Orangeburg sandy loams listed. Therefore, the moisture-holding capacity is about 1.0 to 1.2 inches of water per foot of soil in the root zone. The principal crops grown on this farm are corn and cotton. Information in Table 1 indicates that the normal depth of the soil moisture reservoir for cotton and corn is from 1 to 1.5 feet. Combination of this figure with the moisture-holding capacity per foot shows that the expected total moisture-holding capacity of this soil would be between 1 inch and 1.8 inches. Figures 4, 5, 6, and 7 show the probable number of droughtdays that may be expected from March through November on 1-inch and 2-inch soil moisture capacity soils in Alabama. At Auburn on 1-inch soil in 2 years out of 10, at least 120 droughtdays would be expected, Figure 4. As many as 100 drought-days would occur 5 years out of 10, Figure 5. On a 2-inch capacity soil, the expected number of drought-days would be about 90 and 70 for these probabilities, Figures 6 and 7. Therefore, crops on this soil at Auburn may be expected to suffer from drought quite frequently.

28

28AAAAARCLUALEPRMN

ALABAMA

AGRICULTURAL

EXPERIMENT

STATION

TTO

LEGEND

0I Limestone Valleys LJAppalachian Plateau
SUpper

Coastal

Plains

LILower Coastal Plains LIIPiedmont Plateau
' Black Belt
..... .

r . .-

~-

. r..

AGRICULTURAL

DROUGHT

in

ALABAMA

29

In order to determine when drought-days may be expected, one must determine from Figure 2 in which drought area one resides. In the case of Auburn it is Area E. Data on Area E are based on 25 years of records from Auburn, Clanton, and Montgomery, Table 2. The distribution of drought-days by 10-day periods for 1- and 2-inch base soils in Area E is presented in Figure 12. The number of drought-days shown is the minimum that may be expected in 5 years out of' 10. The greatest probability of drought is in May and October. The May drought is the most serious for summer crops and the fall drought is serious for fall-planted crops. In 1 out of every 2 years on a 1-inch soil, 7 days out of 10 in late May may be expected to be drought-days. During June the frequency of drought gradually drops off to 4 days out of 10 in the first 10 days of July. From about July 5 to August 15 the probability of drought is 3 or 4 days out of 10. About the middle of August, it begins to go up again and reaches a maximum of 8 days out of 10 in late October. Then it drops rapidly until the frequency of any drought is less than 5 years out of 10 in late November. On 2-inch base soils, the pattern of drought expectancy is the same but the frequency is less. Droughts occur 6 days out of 10 in late May and early June but drop off during June and July. Probability of drought is less than 5 chances in 10 during late July and early August for soils that will hold 2 or more inches of available water. Drought increases on these soils in late August, September, and October. Information on the occurrence of drought can be useful only if it helps to find ways to reduce damage caused by drought. How then, can the data presented here be used? The most direct method of reducing damage from drought is by irrigation. Drought frequency data can be used to indicate the need for irrigation. These data give the odds on the need for supplemental water on the various soils and locations. They also indicate the season of the year when drought is most likely to occur. Such information is useful in determining the best time to plant certain crops in order to obtain good stands and to make the period of maximum water needs by a crop coincide with periods when rain is most likely. Planning of other operations, such as land preparation and harvesting, should be more effective if this information is properly used.

30

ALABAMA AGRICULTURAL EXPERIMENT

STATION

SUMMARY and CONCLUSIONS An estimate of drought occurrence in Alabama was made on a basis of past climate records. The 25-year record (1930-1954) of daily precipitation from 27 stations was used in this study. Estimated values of daily evapotranspiration were calculated by use of the Penman formula. The state was divided into northern and southern evapotranspiration areas. By use of the precipitation and evapotranspiration data, daily soil moisture balances were computed and the daily soil moisture balances were used to determine the number of drought-days. Drought occurrence was described in terms of number of drought-days for four root zone soil moisture storage capacities (base amounts) and at four probabilities. The base amounts were 1, 2, 3, and 5 inches and the odds were 1, 2, 3, and 5 years out of 10. Drought-days were classified on an annual, monthly, and 10-day period basis. Monthly and 10-day period drought-days were summarized by dividing Alabama into 9 areas. The same nine areas were used as a basis of summarizing data on excess moisture occurrence and on irrigation water requirements. Based on the estimated number of drought-days occurring yearly, it may be seen that drought is quite common in Alabama. In 1 year out of 10 on soils that will hold an inch of available water, 140 drought-days may occur in central and southeastern Alabama, and in 5 years out of 10 the expected number is more than 110 drought-days. Northern and southwestern Alabama have fewer expected drought occurrences. On a monthly basis, drought-days occurred in all months from April through October. The numbers of drought-days are greatest during May and June throughout the State, whereas southern Alabama has an equally large number in October. At odds of 5 years out of 10, or every other year, with 1-inch base amount of soil moisture in most areas of Alabama, more than one-half of the days in the 2nd and 3rd 10 days of May and August were drought-days. In all 10-day periods in June, one-half or more of the days were drought-days. Lowest numbers of drought-days in most areas were in the 2nd and 3rd 10 days of July, the 1st 10 days of August, and in the 2nd 10 days of September. In general, it can be expected that crops will be subjected to serious droughts in Alabama during the summer
growing season.

AGRICULTURAL

DROUGHT

in

ALABAMA

31

The moisture excess occurs primarily during the months of December through March. In 5 out of 10 years, an annual excess of 12 to 18 inches of precipitation is found in all areas of the state except near the Gulf Coast where the excess is 25 inches. To provide a sufficient supply of water for the numerous periods of drought during the summer months, the excess precipitation must be made available for irrigation purposes from impounded waters, deep wells, and streams. The amount of water required for irrigation that would suffice for 9 out of 10 years is presented in Table 4 for the 4 base soil moisture amounts for each of the 9 areas in Alabama. This study has clearly shown that drought occurrence is to be expected during the summer and fall in Alabama. As a result there are even odds that optimum crop yields cannot be attained because of this drought hazard. The data also reveal that drought occurrence depends markedly upon the amount of water available in the root zone. This suggests that some of the drought hazard can be removed by growing varieties of crops with extensive root systems and by using soil management practices to improve soil properties for optimum root growth. For example, the available water would be increased from 1 to 2 inches if the principal root occupancy zone were increased from 1 to 2 feet. Thus the number of drought-days would be reduced approximately 50 per cent. While crop varieties with more extensive root systems and soils with properties for better root growth would decrease drought occurrence, supplemental water will still be required in producing maximum yields. This means that a source of water for irrigation is needed. To provide water for irrigation will require long-range planning for utilization of the water resources of Alabama. Such plans, which include industrial and municipality needs, must be considered together with present day projects for development of water resources to generate electricity and to provide navigable streams.

32

ALABAMA

AGRICULTURAL

EXPERIMENT

STATION

LITERATURE CITED

(1)
(2)

ASLYING, H. C. Water Comsumption in Plant Production.

In: Ency-

clopedia of Plant Physiology. Vol. III Ed. W. Ruhland, pp. 685-695. Springer-Verlag. Berlin. 1956.
BURTON, GLENN W., DE VANE, E. H., AND CARTER, R. L. Root Pene-

tration, Distribution, and Activity in Southern Grasses Measured by Yields, Drought Symptoms, and P32 Uptake. Agron. Jour. 46:229-233. 1954.

(3) COILE, T. S. Distribution of Forest Tree Roots in North Carolina Piedmont Soils. Jour. Forestry 35:247-257. 1937.

(4)

COOPER,

A. W., SANDERS, C. M., STEPHENS, M. E., AND KUMMER, F. A. Phyiscal Properties of Selected Alabama Soils Related to Supplemental Irrigation Design. Eastern Section of Soil and Water Management. Soil and Water Conservation Research Branch ARS Special Rept. No. 61. 1954.
COWART, F. F. Root Distribution and Root and Top Growth of Young Peach Trees. Amer. Soc. Hort. Sci. Proc. 36:145-149. 1988.
HALL, W.S., CHANDLER, W.

(5)
(6)

AND ANDERSON,

J.

F., VAN BAVEL, C.

H.

M., REID, P.

H.,

H.

A Tracer Technique to Measure Growth and

Activity of Plant Root Systems. North Carolina Agr. Expt. Sta. Tech. Bul. 101. 1953.

(7) (8)

LAIRD, A. S. A Study of the Root Systems of Some Important Sod

Forming Grasses. Fla. Agr. Expt. Sta. Bul. 211. 1930. A. Influence of Sod and Other Factors Upon the Distribution of Small Tung Roots in Ruston Sandy Loam. Amer. Soc. Hort. Sci. Proc. 42:11-16. 1943.
LEONARD, O.

(9) LULL, H. W. Evapotranspiration: Excerpts from Selected References. Southern Forest Expt. Sta., U. S. Forest Service, Occasional Paper 131. 1953.

(10)

J. Root Habits of Longleaf Pine and Associated Species. Ecology 20:47-57. 1939.
PESSIN, L. Use in Irrigation. In: Water, Yearbook of Agriculture, pp 846-858.

(11) THORNTHWAITE, C. W., AND MATHER, J. R. The Water Budget and Its
U. S. Dept. Agr. 1955.
(12) UPCHURCH,

R. P.,

AND LovvoRN,

R.

L.

Gross Morphological

Root

Habits of Alfalfa in North Carolina. Agron. Jour. 43:493-498. 1951.

(13) U.S.D.A.-A.P.I. Agricultural Experiment Station - "Sprinkler Irrigation
Guides for State of Alabama"
-

Lithoprinted. 1954.

(14) VAN BAVEL, C. H. M. A Drought Criterion and Its Application in
Evaluating Drought Incidence and Hazard. Agron. Jour. 45:167-172. 1953.

AGRICULTURAL DROUGHT in ALABAMA

33

(15) (16) (17)

VAN BAVEL, C. H. M., AND VERLINDEN, F.

J.

Agricultural Drought in

North Carolina. North Carolina Agr. Expt. Sta. Tech. Bul. 122. 1956.
VAN BAVEL, C. H. M., AND LILLARD, J. H. Agricultural Drought in

Virginia. Virginia Agr. Expt. Sta. Bul. 128. 1957.

VAN BAVEL, C. H. M., FORREST, L. A., AND PEELE, T. C. Agricultural

Drought in South Carolina. South Carolina Agr. Expt. Sta. Bul. 447. 1957. (18)
VAN BAVEL, C.

H.

M., AND CARREKER,

J.

R.

Agricultural Drought in

Georgia. Georgia Agr. Expt. Sta. Tech. Bul. N. S. 15. 1957.

(19)

WONSER, C.

H., STRIKER, M.

AND SHERARD, HOYT.

M., BRACKEEN, L. G., MCINTYRE, C. L., Soil Survey of Lee County, Alabama. U.S.D.A.

and Ala. Dept. of Agriculture and Industries. Series 1988. 1950.

No. 28.

34

ALABAMA AGRICULTURAL

EXPERIMENT STATION

APPENDIX

Minimum Number of Drought-Days

APP. FIGURE 1. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Muscle Shoals, Ala. (Area A).

AGRICULTURAL

DROUGHT

in

ALABAMA

AGRICULTURAL

DROUGHT in ALABAMA

35
35

APP. FIGURE 2. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Scottsboro, Ala. (Area B).

Percentage

SMinimum

Number of Drought-Days

APP. FIGURE 3. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Gadsden, Ala. (Area C).

36

ALABAMA AGRICULTURAL

EXPERIMENT

STATION

APP. FIGURE 4. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Greensboro, Ala. (Area D).

Minimum Number of

Drought-Days

APP. FIGURE 5. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Auburn, Ala. (Area E).

AGRICULTURAL

DROUGHT

in

ALABAMA

37

AGRICULTURAL DROUGHT in ALABAMA
ercen tage

37

IMinimum

Number of Drought-Days

j

APP. FIGURE 6. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Mobile, Ala. (Area F).

APP. FIGURE 7. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Riverfalls, Ala. (Area G).

38
Percentage 96

ALABAMA AGRICULTURAL

EXPERIMENT

STATION

Ozark

Ala.

7 6

42"Base

jamoant

2__-5"Bose

amoant

.

[3Base 20 40 60 80
Namber

amaant 120 140F 160 180

100 af

Minimam

Drought - Days

APP. FIGURE 8. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Ozark, Ala. (Area 11).

Percentage

I

Minimum Number at Draught-Days

APP. FIGURE 9. Probability for minimum number of droughtdays to occur in period March through November for 4 different values of soil moisture capacity in inches, Robertsdale, Ala. (Area 1).

APPENDIX

TABLE

1.

AVERAGE DAILY EVAPOTRANSPIRATION

IN INCHES

OF WATER

FROM SELECTED

STATIONS'

FOR THE NORTHERN

AREA OF ALABAMA, 1930-56

Year 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954
1955

Jan.
In.

Feb.
In.

Mar.
In.

Apr.
In.

May
In.

June
In.

July
In.

Aug
In. In. In. In. In.

.027 .032 .030 .032 .031 .026 .026 .018 .032 .036 .024 .032 .034 .029 .029 .024 .019 .019 .018 .020 .017 .026 .024 .028 .028
.027

.068 .056 .050 .036 .050 .046 .042 .047 .058 .055 .036 .042 .037 .058 .045 .033 .052 .053 .031 .041 .052 .041 .043 .051 .068
.040

.061 .068

.067 .061 .065 .072 .067 .074 .084 .080 .077 .084 .065 .054 .071

.071 .076 .050 .058 .065 .058 .050 .066 .063 .065
.071

.136 .108 .117 .103 .099 .087 .100 .111 .118 .117 .096 .111 .130 .116 .104 .106 .108 .090 .119 .091 .101 .092 .102 .104 .120
.123

.137 .142 .149 .174 .150 .148 .178 .144 .146 .124 .151 .170 .139 .152 .151 .115 .100 .130 .148 .142 .110 .162 .143 .129 .112
.145

.192 .207 .175 .194 .180 .169 .210 .180 .163 .162 .174 .163 .167 .188 .196 .142 .144 .142 .180 .133 .156 .152 .196 .177 .194
.159

.190 .167 .180 .147 .161 .173 .160 .166 .146 .176 .142 .147 .147 .134 .155 .119 .108 .156 .144 .138 .114 .167 .190 .152 .184
.147

.149 .146 .153 .133 .123 .152 .157 .148 .166 .143 .163 .139 .124 .153 .120 .142 .113 .138 .141 .103 .120 .157 .123 .163 .162
.163

.102 .158 .118 .138 .122 .107 .120 .124 .124 19 .146 .151 .115 .105 .090 .117 .111 .104 .093 .112 .115 .128 .143
.120

.106 .108

.076 .094 .072 .082 .088 .087 .070 .065 .104 .9 .096 .082 .072
.070

.040 .057 .040 .053 .054 .041 .044 .040 .053 00 .043 .045 .050
.052

.022 .024 .018 .032 .022 .024 .024 .026 .031 .3 .026 .030 .022
.024

0 c =

.088 .068 .079 .072 .071 .050 .080 .076 .081 .098 .075
.076

.037 .042 .040 .030 .035 .049 .035 .032 .042 .048 .042 .046 .043

1956 .023 .040 .076 .114 .147 .165 .048 .067 .107 .142 .173 Av. .026 'Anniston and Birmingham, Ala., Chattanooga, Tenn., and Atlanta, Ga.

.161 .154

.157 .141

.131 .120

.069 .080

.043

.019 .016 .030 .024 .020 .022 .016 .027 .025 .024 .023
.024

.031 .024
A

APPENDIX TABLE 2.

AVERAGE DAILY EVAPOTRANSPIRATION IN INCHES OF WATER FROM SELECTED AREA OF ALABAMA, 1930-56

STATIONS

1

FOR THE

SOUTHERN

Year 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944

Jan. In. .039 .044 .042 .038 .044 .048 .039 .031 .040 .050

Feb. In. .082 .082 .065 .047 .066 .072 .055 .058 .081 .062

Mar. In. .074 .090 .083 .095 .087 .095 .096 .087 .101 .098

Apr. In. .146 .138 .135 .117 .118 .128 .126 .135 .128 .135

May In. .155 .135 .151 .176 .142 .171 .166 .175 .147 .137

June In. .192 .207 .188 .195 .184 .189 .215 .184 .170 .163 .157 .140 .162 .184 .200 .200 .183 .172 .196 .158 .183 .181 .222 .184 .210 .187 .150 .185 Jackson,

July In. .182 .170 .188 .144 .169 .158 .159 .182 .137 .165 .138 .138 .172 .166 .170 .146 .147 .189 .166 .140 .131 .182 .183 .162 .172 .152 .154 .162 Miss., and

Aug. In. .155 .166 .141 .160 .145 .145 .177 .144 .167 ,139

Sept. In. .113 .161 .124 .164 .142 .140 .146 .128 .133 .136

Oct. In. .094 .107 .088 .098 .101 .118 .099 .083 .109 .104 .113 .094 .102 .098 .115 .092 .105 .095 .094 .075 .099 .105 .099 .108 .108 .097 .084 .100

Nov. In. .045 .073 .052 .072 .069 .068 .060 .052
.065

Dec. In. .033 .032 .020 .054 .040 .034 .032 .040 .042 .048 .033 .036 .033 .035 .040 .030 .056 .034 .034 .036 .072 .039 .032 .030 .041 .030 .042 .038

w

.060 .052 .054 .072 .070 .059 .066 .053 .043 .047 .072 .061 .056 .053 .057 .059 .054 .064 .060

.171 .100 .048 .078 .035 .124 .167 .054 .063 .046 .146 .158 .076 .054 .048 .168 .078 .143 .080 .041 .042 .064 .088 .115 .180 .166 .136 .111 .060 .046 1945 .146 .151 .079 .098 .033 1946 .163 .081 .127 .033 .076 1947 .174 .079 .149 .048 .035 1948 .170 .054 .080 .108 1949 .037 .162 .080 .123 .082 1950 .042 .046 .071 .076 .120 .176 1951 .134 .152 .060 .083 1952 .039 .078 .120 .157 1953 .044 .052 .135 .085 .085 .144 1954 .038 .094 .126 .162 .037 .056 1955 .147 .055 .082 .120 1956 .037 .066 .086 .130 .160 Av. .041 1 Mobile and Montgomery, Ala., Macon and Thomasville, Ga.,

.162 .147 .144 .128 .130 .143 .115 .174 .142 .133 .144 .167 .106 .145 .147 .166 .123 .153 .148 .123 .166 .117 .189 .117 .155 .122 .157 .140 .201 .164 .162 .128 .127 .162 .134 .158 Pensacola, Fla.

c r
m

* 0 m Z

z

2 01

1

300
APPENDIX TABLE 3. MINIMUM NUMBER OF DROUGHT-DAYS IN ALABAMA-BY AREAS FOR DIFFERENT MONTHS, CAPACITIES, AND PROBABILITIES, 25-YEAR AVERAGE SOIL STORAGE a

AreaA

AreaB

AreaC
5

AreaD
1

AreaE

C 5f? C

Month

Prob.

Base amounts
1" 2"

3"

Base amounts
1"

5"P

2"

3"P

"P

1,'

Base amounts
2"

3

Base amounts
5

"

"

1',

2"

3P"5"

Base amounts
1,' 2"
3"P

F-I

Minimum

drought-days
0 0 0 0 0 0 00 00 00 0 0 0 0 6 4 3 800 9 0 0 16 0 0 6 14 00 0 123 0 0 0 0 0 0 0 0 0
C -I
sw

Feb.

2/10 3/10 5/10
Mar.

1/10 1/10 1/10

10000 20000 30000 50000 10000 11 20000 6 30000 50000 S 10 18 14 28200 9 14 33000 21 17 19 23 0 0 7 2 0 0 0 0 0 3 2

0 0 0 0
0

0 0 0 0
0

0 0 00 00 00
0

0

2/10 3/10 5/10
Apr.

0000

2/10 3/10 5/10 May 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 2/10 3/10 5/10 I II

14 08000 5 0 11
4 0

0

0 0

0 0 4 1 0 0 19 12 7 0

14 11 24 21 18 14 25 22 19 16 23 20 17 13

5 0 21 16 12 6 25 20 17 12 22 17 13 7

0 0 14 8 4 0 25 19 15 8 20 15 11 5

0 0 1 0 0 0 17 11 7 1 17 12 8 1

242

262

26 23 21 18

0 01 15 18 1 00 0 0 15 00 110
3 1

15 12 11 25 23 21 17

7 5 2 21 18 16 12

0 0 0 19 14 11 6 24 20 18 13

0 0 0 7 4 1 0 21 16 12 6

170 13 2 22

24 20 17 12 25 22 19 15

20 15 11 6

15 10 6 0

26 24 22
19 16 22 18

222

25 23 62 0 2 01
8 1 1 2 9 1 5

1

1 15 01

1

1

June

20 19 18 1 218 167 1 110 4 9 14 11

24 23 20 18 17 15 12 9

22 2019 19 01 2318 1215 216 13 120 11 12 81 6 5
12 8

25 25 23 22 20 19 17 14 22 18 16 12

July

1/10

R rr R r-

IL-

I

24 23 23 20 20 18 17 13 18 14 12 9 5 13 i~ IL 1 8 Lln II

20 20 18 17 16 14 13 13 11 9 7 5 Continued

APPENDIX TABLE 3

(CoNT'D).

MINIMUM NUMBER OF DROUGHT-DAYS IN ALABAMA BY AREAS FOR DIFFERENT MONTHS, STORAGE CAPACITIES, AND PROBABILITIES, 25-YEAR AVERAGE

SOIL

Month

Prob.

Area A Base amounts
1,, 2

Area B Base amounts
507

AreaC Base amounts
5

AreaD Base amounts
PP 1

AreaE Base amounts
5"?
1"

3"

1"

2"

3~P

PP

1,

"

3PP

5

2"

30P1

2"

3"

5P

Aug.

1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10

26 24 23 23 23 20 17 16 20 16 14 11 16 11 8 4 25 24 24 22 21 19 18 16 18 15 14 12 13 9 7 6
25232322

Minimum draught-days 21 181513 25 22 19 16 18 14117 21 17 13 11 73 19 14 10 7 16 11 15 8 5 2 13 6 20 26 24 23 20 21 19 18 15 19 15 14 11 14 9 7 5
253222

28262422 24211715 2116129 161040 25252421 21211916 19181611 161182
28282727

22181716 19141210 171286 14830 26252421 22202015 20171610 16128
26 262626

a-

a a

Sept.

25 242219 21 191613 18 16128 1410 50
25232221

Oct.

1/10

21 20 1918 18 17 1514 13 10 50 87 6 4 54 4 2
0 0

21 17 1616 17 1210 10 12.4 00 9 7 50 30 00
00

21 18 1715 18 15 1210 3 1496 1211 8 5 4 2 0 0
0 0

26 25 2523 24 23 2119 21 18 1511 20 19 1917 16 14 1412 13 11 119 41 65
42 21

24 2322 22 22 2018 16 19 148 1 18 16 13 8
4

C

Nov.

Dec.

1/10 2/10
3/10 5/10

76 21 00 00
00

77 00 00 00
00

98 42 00 00
00

1817 16 1514 12 1211 8 74 0
11 1

m

0 0 0

0 0 0

00 00 00

00 000 00

00 00

0

0 0 0

0 0 0

00 00 00

00 00 00

00 00 00

2 0 0

00 00 00

0 0 0

z
-I

Continued

z

APPENDIX

TABLE 3

(CoNT'D).

MINIMUM NUMBER OF DROUGHT-DAYS IN ALABAMA BY AREAS FOR DIFFERENT MONTHS, STORAGE CAPACITIES, AND PROBABILITIES, 25-YEAR AVERAGE

SOIL 1;A

Month

Prob.
1"

Area F Base amounts
2"
3~P

AreaG Base amounts
5??

AreaH Base amounts
5,,
1" 2"

AreaI Base amounts
5~

C
3-4 5P

1"

2"

3,

3"

1~

2"

3PP

C

Feb.

1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10
2/10

0 0 0 0 10 7 5 1 16
13

0 0 0 0 0 0 0 0 9
5

0 0 0 0 0 0 0 0
0 0

0 0 0 0 0 0 0 0 '0 0
0 0

Minimum 0 0 0 0 0 0 0 0 8 5 3 0
16 13

drought-days 0 0 0 0 0 0 0 0 0 0 0 0
0
0

7 5 3 1 8 6 4 1

0 0 0 0

Mar.

0 0 0 0 9
5

0 0 0 0
0

0 0
0 0

0 0 0 0 0 0 0 0
0
0

0 0 0 0 0 0 0 0
0

9 7 5 1 13 8 4 1
2114

0 0 0 0 0 0 0 0 9 6 1

0 0 0 0 0 0 0 0
0

0 0 0 0 0 0 0 0
0

0 C -I

Apr.

3/10 5/10 May 1/10 2/10 3/10 5/10 '1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10

11 9

2 0

0 0

11 7

3 0

0 0

0 0 0 7 0 0 0

1710 13 7 11 4 8 1

0 0

0 0 0 4 0 0

17 14 9

0 0. 0

0 0 0 1 0 0 8 5 0 7 0 0 0
WA

26 22 18 231815 21 16 12 17 12 7 25 22 19 15 23 19 16 12 2320 1815 1511 10

6 4 2 0

23 21 17 201814 18 16 11 16 12 6 26 22 20 16 24 20 17 13 2319 1915 1612 11

26252411 232018 20 17 12 17 11 3

22212012 201815 18 16 12 15 12 6 23 22 2013 21 18 15 18 15 11 13 9 5 13 11 11 10 5 1 7 0 0 2 0 0

June

5

7

25 24 24 21 23 21 2117 21 19 1813 17 14 12 3 19 16 1615 16 15 1410 13 9 9 9 5 4

July

21 20 1915 17 14 1310 14 10 9 11 7 5

7 4

19 17 1715 15 13 1210 13 9 8 7 2 0

4 0

7 2

Continued

APPENDIX

TABLE 3

(CoNT'D).

MINIMUM NUMBER OF DROUGHT-DAYS IN ALABAMA BY AREAS FOR DIFFERENT MONTHS, STORAGE CAPACITIES, AND PROBABILITIES, 25-YEAR AVERAGE

SOIL

Month

Prob.
1

Area F Base amounts
2" 3P
5P

AreaG Base amounts
1" 2"
3

AreaH Base amounts
5

AreaI Base amounts
5~P1~

"

,P

1"

2"

3PP

2"

3PP

5

PP

Aug.

1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10

20 17 15 12 24 21 18 14 28 25 22 18

15 12 10 6

12 7 4 0 21 18
14

10 3 0 0 16 14 3 0

Minimum drought-days 19 15 12 8 16 11 8 1 14 8 4 0 10 3 0 0 22 19 17 13 28 25 22 18 20 16
12

19151110 1611 14 8 10 4

6 3 0

4 0 0 9
4

1711 13 7 11 4 8 0

7 0 0 0

6 0 0 0 2 0
0

aF

Sept.

16 9

21 19

0

7

17 11 7 0

11 4 1 0

27262416 211815
181410

231714 1712 8
13 7 4

14 28 26 24 21

9 27 25 21 15

5

0

6

1

0

0
C

Oct.

27 2726 23 2015 19 14 5 13 4 0 8 4 1 0 2 0 0 0

25 2522 21 2014 18 16 6 0 14 6

2624 2218 1810 10 0

26 2219 14 23 19 12 0 21 16 7 0 17 10 0 0 18 17 15 14 12 10 11 7 6 6 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0

Nov.

21 17 16 15 11 11 11 8 7 4 3 2 6 1 0 0 3 0 0 0 3 0 0 0

21 20 2016 18 17 15 7 15 14 12 0 9 8 4 0 8 3 0 0 6 1 0 0 6 0 0 0 4 0 0 0

23 22 2221 20 19 1815 17 16 1510 12 9 8 0 10 5 2 0 6 0 0 0 6 0 0 0 2 0 0 0

m m

Dec.

0 0 0 0

z
-I -{ 0

z

AGRICULTURAL

DROUGHT

in

ALABAMA

45 A
BY

APPENDIX TABLE 4.
10-DAY

MINIMUM

NUMBER OF DROUGHT-DAYS IN AREA
SOIL STORAGE CAPACITIES AND

PERIODS

FOR DIFFERENT

PROBABILITIES,

25-YEAR AVERAGE

Month

Prob.

1st to 10th Base amounts 1" 2" 3" 5" 0 0 0 0 2 0 0 0 10 8 6 3 10 10 9 7 9 7 6 4 10 9 8 4 10 8 6 4 10 10 8 5 8 5 3 0 0 0 0 0 0 0 0 0 8 4 0 0 10 9 8 6 9 7 6 3 10 8 6 1 10 8 6 3 9 7 5 1 7 4 2 0 5 0 0 0 10 9 7 4 9 7 5 2 9 7 5 0 10 7 5 2 8 6 4 1 6 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 4 1 0 8 5 3 0 8 5 3 0 9 6 4 1 8 6 3 0 6 2 0 0

11th to 20th Base amounts 1" 2" 3" 5" Minimum drought-days 1 0 0 0 8 6 4 00 10 10 8 6 10 10 8 6 10 10 9 6 10 8 7 5 10 8 7 4 10 9 8 5 0 0 0 0 0 0 0 0 9 7 6 2 10 9 8 5 1 9 7 4 8 7 5 3 9 8 6 2 10 8 7 3 0 0 0 0 0 0 0 6 2 0 0 10 9 8 4 1 10 8 6 3 8 6 4 0 9 8 6 0 10 8 6 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10 8 6 0 9 7 5 0 8 6 4 0 9 8 6 0 9 7 5 0 0 0 00 0

21st to 31st Base amounts 1" 2" 3" 5" 2 0 0 0 9 6 4 1 11 10 8 5 10 10 10 8 9 8 7 5 11 11 10 7 10 10 8 6 11 9 7 4 0 0 0 0 0 0 0 0 4 0 0 0 11 8 6 3 10 10 9 7 9 7 6 2 11 11 9 5 10 7 5 2 10 8 6 2 0 0 0 0 0 0 0 0 0 0 0 0 11 7 3 0 10 10 9 5 9 6 5 1 11 11 8 3 9 6 4 1 10 7 5 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 10 9 7 3 8 6 3 0 11 9 6 0 9 6 4 0 10 7 5 0 0 0 0 0

Mar.

1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 8/10 5/10

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

3 0 0 0 000 0 0

Continued

46

46 ALABAMA AGRICULTURAL EXPERIMENT STATION
IN AREA AND

APPENDIX TABLE 4 (CONT'D). MINIMUM NUMBER OF DROUGHT-DAYS B BY 10-DAY PERIODS FOR DIFFERENT SOIL STORAGE CAPACITIES PROBABILITIES, 25-YEAR AVERAGE

Month

Prob.

1st to 10th Base amounts
1" 2"
3"P 5"

11th to 20th Base amounts
1" 2"
3

21st to 31st Base amounts
51

"P

1"

2"

3

it*
5

Mar.

1/10 2/10 3/10 5/10 2/10 3/10 5/10

0 0 0 0 2 1 0 0 9 7 6 3 10 9 8 5

0 0 0 0 0 0 0 0 7 4 0 0 10 9 7 2

0 0 0 0 0 0 0 0 4 1 0 0
9

0 0 0 0 0 0 0 0 0 0 0 0 6 2 0 0
9

Minimum drought-days 10000 I0000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8 6 4 1 0 0 0 0 0 0 0 0 6 3 0 0

00

Apr.

1/10

1 0 109 10 10 10 10 4210 10
5 10

0 10 8

May

1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 2/10 3/10 5/10

10 9 9 7 8 5 62

10 9

June

7 5 0
9

10 .10 9 9 7 7 7 6 5 5 3 1 10 9 8 5 9 7 5 2
9

11
6 11

10
4 9

10

July

1/10

9 9 8 7 7 6 5 4

7 5 1

6 3 0
9

7 3 1 6 3 2 0

11

1 9 7 875 10 109

6

Aug.

2/10 3/10 5/10
Sept.

1/10 1/10

10 10 10 8 7 6 6 5 4 4 0 0 10 10 10 7 9 8 5 7 6 1 5 3 10 9 9 6 7 4 4 1 8 4 2 0 r 6 3 0 0r 9 6 3 0 6 1 0 0

5 2 0
9

10 8 8 6 7 4 5 1 10 9 8 4 10 9 7 4 3 0 0 0

1110

2/10 3/10 5/10
Oct.

6 3 0
9

10 10 8 8 7 6 1 1 9 7 5 0 0 0 0 0
9

7443 1110 10 986

109

2/10 3/10 5/10
Nov.

1/10

6 3 0 5 0 0 0

6 2 0 0 0 0 0

2/10 3/10 5/10 r

1/10

40006 0 0020 998 100100 876 00007 00004 620 977 Continued

'AGRICULTURAL

DROUGHT

in

ALABAMA

47

APPENDIX TABLE 4 (CONT'D). MINIMUM NUMBER OF DROUGHT-DAYS IN AREA C BY 10-DAY PERIODS FOR DIFFERENT SOIL STORAGE CAPACITIES AND PROBABILITIES, 25-YEAR AVERAGE

Month

Prob.

1st to 10th Base amounts
1" 2" 3" 5"

11th to 20th Base amounts
1" 2"
3"

21st to 31st Base amounts
1" 2" 3" 5"

5"

Minimum drought-days Mar. 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 8/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 0 0 0 0 3 2 0 0 9 7 5 3 10 9 8 6 9 7 6 4 9 8 6 8 10 9 8 5 10 9 7 5 10 6 2 0 0 0 0 0 0 0 0 0 7 3 1 0 10 9 7 4 8 7 5 2 9 6 4 1 10 8 6 3 10 7 6 2 9 5 1 0 0 0 0 0 0 0 0 0 3 0 0 0 10 8 6 3 8 6 4 1 8 4 2 0 9 7 4 0 9 7 5 0 8 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 1 0 0 7 4 2 0 6 2 0 0 8 4 1 0 9 6 2 0 7 1 0 0 0 0 0 0 8 6 4 1 10 10 8 6 10 9 8 5 10 9 8 5 8 7 5 3 10 10 8 4 10 10 8 5 4 0 0 0 0 0 0 0 1 0 0 0 9 7 6 2 1 8 7 4 1 7 6 3 7 5 3 0 10 9 6 0 10 8 6 2 2 0 0 0 0 0 0 0 0 0 0 0 5 2 0 0 10 1 7 5 3 10 1 7 5 1 6 4 1 0 10 8 4 0 10 6 4 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 9 5 2 0 8 6 4 0 5 2 0 0 9 5 2 0 9 5 2 0 0 0 0 0 0 0 0 0 10 6 4 1 11 9 8 4 0 0 0 0 4 1 0 0 10 8 6 3 0 0 0 0 0 0 0 0 9 5 8 0 0 0 0 0 0 0 0 0 1 0 0 0 9 6 1 0 8 4 1 0 6 2 0 0 10 6 3 0 9 8 5 0 0 0 0 0

Apr.

May

June

101010 9 9 9 7 5 5 2 5 4 10 8 6 4 11 10 8 6 10 10 9 5 11 10 9 6 2 0 0 0 9 7 5 1 9 8 5 2 10 8 7 3 10 8 7 1 0 0 0 0 9 6 4 0 8 5 3 0 10 7 5 0 10 8 7 0 0 0 0 0

July

Aug.

Sept.

Oct.

Nov.

Continued

48

48 ALABAMA AGRICULTURAL EXPERIMENT STATION

APPENDIX TABLE 4 (CONTD). MINIMUM NUMBER OF DROUGHT-DAYS IN AREA D BY 10-DAY PERIODS FOR DIFFERENT SOIL STORAGE CAPACITIES AND PROBABILITIES, 25-YEAR AVERAGE

Month

Prob.

1st to 10th Base amounts 1" 2" 3" 5" 2 0 0 0 5 3 2 0 10 9 7 5 10 10 9 7
10

11th to 20th Base amounts 1" 2" 3" 5" Minimum drought-days 1 0 0

21st to, 31st Base amounts 1" 2" 3" 5"
1 0 0 0

Mar.

1/10 2/10 3/10 5/10 1/10 2/10 8/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 2/10 3/10 5/10

0 0 0 0 0 0 0 0 9 7 5 0 10 9 8 5
9

0 0 0 0 0 0 0 0 7 2 0 0 10 9 7 4
9

Apr.

0 0 0 0 0 0 0 0 8 5 2 0 9 6 4 1 8 5 1 0

10 10

10 8

7 5

0 0 0 0 0 0 0 0

7 10 8400 6200 11 11 10 9 8750 6310 10 10 10 9 9886 7662

1

0

May

10 8 10 9

3 0 10 8

10 10

10 10

10

June

90 8 5 4 0 9 9 6 4 0 8 4 1 0 9 7 3 0
10

July

1/10

8 6 4 10 9 7 5

7 5 3 9 7 5 2

7 5 2 8 5 3 0

10 O777 9 O543 10 0100 10
7 7 5 4

8666 8643 4100 11 11 11 10 9875 7500 10 10 10 9 11 10 10 9 11 8 10 8

Aug.

1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 2/10 3/10 5/10

9

1

0

0

Sept.

Oct.

1/10 1/10

8 10 10 9 7 6 98 3 5 86 2 0 54 9876 107520 10 10 10 10 9 8 8

10

10

10

10 10 10 8 9

10 10 9 7 9

10 10 9 5 9

9 7 2 9 6 2 0

11 11 10

11 11 10

11 11 9

11 10 8

Nov.

2/10 3/10 5/10

10 8 6 3

10 10 10 88 7 5 66 32 1

Continued

AGRICULTURAL

DROUGHT

in

ALABAMA

49

AGRICULTURAL DROUGHT in ALABAMA

4

APPENDIX TABLE 4 (CONT'D). MINIMUM NUMBER OF DROUGHT-DAYS IN AREA E BY 10-DAY PERIODS FOR DIFFERENT SOIL STORAGE CAPACITIES AND PROBABILITIES, 25-YEAR AVERAGE

Month

Prob.

1st to 10th Base amounts
1" 2"
3"P 5"

11th to 20th Base amounts
1"

21st to, 31st Base amounts
1" 2"
3"P 5"

2"

3"P

5"

Mar.

2/10 3/10 5/10
Apr.

1/10 1/10

1 0 0 0
5

0 0 0 0 0 0 0 0 9 7 3 0 10 10 9 6 9 8 6 3 8 6 4 0

0 0 0 0 0 0 0 0 7 3 0 0 10 9 8 5 9 8 6 3 8 4 2 0

0 0 0 0
0

Minimum drought-days 4 0 0 0 2 0 0 0 1 0 0 0 0 0 0 0 8 6 5 4 10 10 10 7
9

3

0

0

0

2/10 3/10 5/10 May 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10

3 1 0 10 8 7 5 10 10 9 7 10 8 7 4 9 8 6 4

0 0 0 0 0 0 0
9

2 1 0 0 10 9 8 5
9

0 0 0 0 8 6
5

0 0 0 0 0 0 0 0 8
6

5100

11

10

9

5

1
9

8870 7650 10 10 10 9997 8877
8 7 7 6 6 5

June

7 4 0
9

8 7 6
9

8 7 6
9

8 7
5 9

10

4 0 8 6 4 0 6 2 0 0
9 5

July

7 5 1 8 4 0 0 10 7
4

8 6 4 9 7 6 3

7 5 2 8 5 3 0

7
5 1

1088 6665 5432

Aug.

1/10

2/10 3/10 5/10
Sept.

7 4 1 0 10 8 5 0 10 8 6 2 8 6 3 0

1/10

2/10 3/10 5/10
Oct.

10 10 10 10 9 8 8 8 6 6 4 2 10 9 7 6 10 9 7 4 9 8 6 2 10 9 7 1 9 7 6 0

0 8 7 5 0

10 10 98 8 6 6 2 10 10 10 9 97 7 5 9 7 6 2 8 6 4 0

11 10

10 8

9 6

7 4

0 0 10 7 5 0 7
5

2/10 3/10 5/10
Nov.

1/10

10 10

10 10

10 9

10 7

2/10 3/10 5/10 C/1 rr

1/10

10 10 7 9 4 6 0 n r,I ri0

11 11 10

11 10 9

1 10 8

1 9 6

1 0 Continued

50

ALABAMA

AGRICULTURAL

EXPERIMENT

STATION

APPENDIX TABLE 4 (CONT'D). MINIMUM NUMBER OF DROUGHT-DAYS IN AREA F BY 10-DAY PERIODS FOR DIFFERENT SOIL STORAGE CAPACITIES AND PROBABILITIES, 25-YEAR AVERAGE

Month

Prob.

1st to 10th Base amounts 1" 2" 3" 5" 4 1 0 0 5 3 2 0 10 9 8 5 10 10 8 6 8 7 5 3 9 7 6 3 9 8 7 5 10 10 9 6 10 8 6 3 0 0 0 0 0 0 0 0 10 7 5 1 10 8 7 4 8 6 4 0 5 4 2 0 9 8 7 1 10 9 6 3 10 8 5 2 0 0 0 0 0 0 0 0 8 4 0 0 10 8 7 3 8 6 4 0 5 0 0 0 9 6 2 0 10 7 3 0 9 7 5 0 0 0 0 0 0 0 0 0 0 0 0 8 6 3 0 7 4 2 0 3 0 0 0 4 0 0 0 10 6 1 0 5 2 1 0

11th to 20th Base amounts 1" 2" 3" 5" Minimum drought-days 5 3 1 0 8 7 6 3 10 10 10 7 10 10 9 6 9 8 6 2 8 6 5 3 10 9 7 4 10 10 10 8 9 6 3 0 0 0 0 0 3 0 0 0 10 9 8 5 10 9 8 4 8 6 4 0 7 4 2 0 10 8 5 0 10 10 8 5 6 2 0 0 2 0 3 0 0 0 9 7 4 0 10 9 5 0 6 2 0 0 0 0 0 0 0 0 0 0 9 7 5 2 10 9 6 3 8 0 0 0 0 0 0 0 0 0 0 0 0 8 7 5 0 8 5 0 0 0 0 0 0 7 2 0 0 10 8 0 0 2 0 0 0

21st to 31st Base amounts 1" 2" 3" 5" 5 2 0 0 10 7 6 3 11 10 8 5 10 9 7 5 9 6 4 2 11 9 7 5 10 9 8 6 11 11 10 8 8 5 2 0 0 0 0 0 7 5 3 0 11 10 8 4 10 8 7 3 8 4 2 0 10 7 5 1 10 7 6 2 11 11 10 5 6 3 0 0 0 0 0 0 2 0 0 0 10 8 7 3 10 8 5 2 7 3 1 0 7 4 2 0 9 7 5 0 11 9 7 0 2 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 8 5 4 0 6 2 0 0 3 0 0 0 9 6 0 0 11 6 1 0 0 0 0 0

Mar.

1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

Continued

3

AGRICULTURAL

DROUGHT

in

ALABAMA

51

GRICULTURAL DROUGHT in ALABAMA

5

APPENDIX TABLE 4 (CONT'D). MINIMUM NUMBER OF DROUGHT-DAYS IN AREA C BY 10-DAY PERIODS FOR DIFFERENT SOIL STORAGE CAPACITIES AND PROBABILITIES, 25-YEAR AVERAGE

Month

Prob.

1st to 10th Base amounts 1" 2" 31? 5?? 3 1 0 0 5 3 1 0 10 9 7 4 0 0 0 0 0 0 0 0 10 7 4 2 0 0 0 0 0 0 0 0 7 3 0 0 10 8 7 5 9 6 3 0 6 0 0 0 8 4 2 0 9 6 3 0 10 9 7 0 0 0 0 0 0 0 0 0 0 0 0 0 8 6 3 0 9 4 2 0 5 0 0 0 7 1 0 0 6 1 0 0 8 4 0 0

11th to 20th Base amounts 1" 2" 3" 5?? Minimum drought-days 4 0 00 200 0 0 0 00 0 0 00 8 7 5 3 10 10 9 7 10 10 8 6 8 6 4 2 8 6 5 3 10 8 6 3 10 10 10 7 9 8 7 2 3 1 0 0 0 00 00 00 0

21st to 31st Base amounts 1" 2" 3? 5??
2 5

Mar.

1/10

2/10 3/10 5/10 Apr. 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 2/10 3/10 5/10
Sept.

5 1 0 0

0

0

0am 0o

7

10 8 710 6 3 140
4

May

10 9 8 7 7 50 510 10 8 7 5 7 5 3 0 7 3 0 0 8 6 4 0 10 10 8 3 9 8 65 40 65 42 20 00 4 10 00 00 6 3 00 00 10 7 5 00

0 0 8 6

11 7200 9 8 5 10 9 8 5 000 10 11980
7 7

June

10 10 8 9 8 7 6 5 10 7 5 2 9 7 5 2 9 8 6 4 10 9 8 6 9 6 4 1 7 3 0 0 9 6 4 0 10 8 7 1

4

650

July

530 7 5 430 4 2,420 2 0 10 9 7 5 10 10 8 5 11 11 11 9 6 4 2 0 10 10 10

Aug.

1/10 1/10 1/10

2/10 3/10 5/10
Oct.

2 0 9 4 0

77 10 8 4 740iue

2/10 3/10 5/10
Nov.

2/10 3/10 5/10

1/10

10 10 9 9 8 7 4 4

9 97 8 83 66 0 1 00

52

ALABAMA

AGRICULTURAL

EXPERIMENT

STATION

APPENDIX TABLE 4 (CONT'D). MINIMUM NUMBER OF DROUGHT-DAYS IN AREA H 10-DAY PERIODS FOR DIFFERENT SOIL STORAGE CAPACITIES AND PROBABILITIES, 25-YEAR AVERAGE

BY

Month

Prob.

1st to 10th Base amounts
1" 2" 3" 5"

11th to 20th Base amounts
1" 2"

21st to 31st Base amounts
5" 1" 2" 8"
5

3"

"

Minimum drought-days Mar. 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 2 0 0 0 4 2 1 0 10 9 8 5 10 9 8 7 10 8 5 3 8 6 4 2 10 9 7 5 10 9 8 6 10 10 8 6 0 0 0 0 0 0 0 0 10 8 6 1 10 9 8 5 10 7 5 1 6 3 1 0 10 8 6 2 10 8 7 3 10 10 8 5 0 0 0 0 0 0 0 0 8 5 2 0 10 9 7 4 10 7 5 1 4 0 0 0 9 7 4 0 9 7 5 0 10 9 8 4 0 0 0 0 0 0 0 0 0 0 0 0 9 6 3 0 10 7 4 0 3 0 0 0 8 4 0 0 8 6 0 0 10 7 4 0 6 3 1 0 8 6 5 3 10 10 10 7 10 9 8 6 8 6 5 2 8 7 5 2 10 9 8 5 10 10 10 8 10 9 8 4 0 0 0 0 2 1 0 0 10 8 7 4 9 8 7 5 7 5 3 0 7 4 1 0 9 8 6 3 10 9 8 5 10 9 7 3 0 0 0 0 0 0 0 0 9 7 3 1 9 7 6 3 7 4 3 0 4 0 0 0 8 6 2 0 10 8 6 0 10 8 6 2 0 0 0 0 0 0 0 0 2 0 0 0 7 6 4 1 5 3 1 0 1 0 0 0 7 1 0 0 9 6 0 0 9 6 2 0 4 0 0 0 10 8 6 3 10 9 8 6 10 9 8 6 7 6 5 3 11 9 7 4 10 9 8 6 11 11 11 10 8 5 3 0 0 0 0 0 8 5 2 0 10 9 7 5 10 9 8 5 6 4 2 0 9 6 4 0 10 8 6 4 11 11 10 8 7 5 3 0 0 0 0 0 1 0 0 0 10 8 6 4 9 8 8 5 6 3 0 0 7 3 1 0 10 7 4 0 11 11 9 5 7 5 2 0 0 0 0 0 0 0 0 0 9 4 0 0 9 8 6 1 4 2 0 0 5 1 0 0 7 3 0 0 11 9 6 0 6 3 0 0

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

Continued

AGRICULTURAL

DROUGHT

in

ALABAMA

53
NUMBER OF DROUGHT-DAYS
SOIL STORAGE

APPENDIX TABLE
I BY 10-DAY

4

(CONT'D).

MINIMUM

IN AREA

PERIODS

FOR DIFFERENT

CAPACITIES AND

PROBABILITIES,

25-YEAR AVERAGE

Month

Prob.

1st to 10th Base amounts
1" 2" 3" 5" 1

11th to 20th Base amounts
2" " 5"

21st to 31st Base amounts
1" 2" 5"

Minimum drought-days Mar. 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 1/10 2/10 3/10 5/10 5 3 0 0 6 4 3 0 10 9 7 5 10 9 8 4 7 5 4 1 8 6 5 2 9 6 5 1 10 10 8 4 9 7 5 3 0 0 0 0 0 0 0 0 10 8 6 3 10 7 5 1 5 3 2 0 2 0 0 0 7 3 1 00 9 7 4 0 9 7 5 2 0 0 0 0 0 0 0 0 8 5 2 0 9 7 0 0 5 2 0 0 0 0 0 0 0 0 0 6 3 0 0 8 5 3 0 0 0 0 0 0 0 0 0 0 0 0 0 2 1 0 0 5 0 0 0 0 0 0 0 0 0 0 00 2 0 0 0 1 0 0 0 6 2 0 0 9 7 6 4 10 10 9 6 10 9 7 4 5 3 3 1 6 5 3 1 10 7 4 0 10 10 9 6 8 6 4 1 0 0 0 0 6 3 1 0 10 9 6 3 9 8 6 3 4 2 0 0 2 0 0 0 10 5 1 0 10 7 4 1 7 4 0 0 0 0 0 0 0 0 0 0 8 6 4 1 8 7 5 0 3 1 0 0 0 0 0 0 6 3 0 0 7 2 1 0 6 4 0 0 0 0 0 0 0 0 0 0 4 0 0 0 7 5 2 0 2 0 0 0 0 0 0 0 0 0 0 0 6 0 0 0 0 0 0 0 5 2 0 0 10 8 7 5 11 9 8 6 8 7 5 3 4 3 2 1 9 7 5 3 10 7 6 3 11 11 11 8 8 5 3 0 0 0 0 0 9 7 5 1 10 8 6 4 8 6 4 1 3 1 0 0 8 5 2 0 7 4 2 0 11 10 9 4 4 2 1 0 0 0 0 0 6 2 0 0 9 6 5 2 8 6 4 0 2 0 0 0 4 0 0 0 7 2 0 0 10 7 5 0 4 1 0 0 0 0 0 0 0 0 0 0 6 1 0 0 6 3 1 0 1 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 1 0 0 0

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.