Regional Drought Frequency Analysis

Analysis of severity and duration of droughts in central United States and Massachusetts is compared with available drought data from California, the Clearwater River, Illinois, the Soviet Union, and the Nile River. Considerable basic differences in drought occurrence are found to characterize the different regions. For example, sequential correlation between annual drought flows, which is strongly marked on the Clearwater River, in the U.S.S.R., and in Massachusetts, is not found in central United States rivers examined. Drought flows of central United States rivers examined seem to have a characteristic drought flow approximately 60% to 65% of the annual long term mean, whereas no such phenomenon is found in Massachusetts. The various rivers within each of the two groups show strong basic similarities, with differences apparently mostly of random origin. It is concluded that drought frequency analysis should be conducted within a regional context, including consideration of drought experience on all rivers that are considered to have similar characteristics.