The drought index may be computed for any desired level of mean annual rainfall. But to simplify the computations, five tables of drought factors were made up. Each table covers a specified range of mean annual rainfall. The measurements needed for the drought index are the (1) the maximum air temperature (or the drybulb temperature at time of standard observation) and (2) the total rainfall for the past 24 hours.
Index | Stage |
---|---|
99 | 0 |
199 | 1 |
299 | 2 |
399 | 3 |
499 | 4 |
599 | 5 |
699 | 6 |
800 | 7 |