Relationship between the common climatic parameters and average drought frequency

The parameters commonly considered to define climate are the mean annual precipitation and mean annual potential evapotranspiration. In this study an attempt has been made to develop a relationship between average drought frequency and the evapotranspiration/precipitation ratio for the arid, semi‐arid and subhumid climatic regions of India. The climatic regions are delineated using two climatic indices: namely (i) the ratio of mean annual precipitation (P_a) to global terrestrial mean annual precipitation (P_g), and (ii) the ratio of mean annual potential evapotranspiration (E_p) to mean annual precipitation (P_a). It was noted that the average drought frequency (i e., year^?1.) decreases gradually from dry to wet regions. The return period varies from 2 to 3 years in the arid regions (12>E_p/P_a≥5), 3 to 5 years in semi‐arid regions (5>E_p/P_a≥2), and 5 to 8 years in sub‐humid regions (2>E_p/P_a≥3/4). Another relationship was developed between the average frequency of drought occurrence and the ratio of mean annual deficit to mean annual precipitation, (E_p?P_a)/P_a. The results have been compared with the drought experiences documented for other regions of the world. Copyright © 2001 John Wiley & Sons, Ltd.