The report attempts drought characterization in arid and semi-arid climatic regions of India. Drought frequency and intensity are a function of the dimensionless climatic parameter derived as a ratio of mean annual potential evapotranspiration to mean annual precipitation (Ep/Pa).
The study revealed that the frequency and intensity of meteorological droughts have significant relationship with the Ep/Pa ratio. Average drought frequency is seen to decrease gradually from dry to wet region, from once in two-three years in the arid zones (12>Ep/Pa≥5) to three to five years in the semi-arid regions (5>Ep/Pa≥2). Also, similar relationship is obtained between the average drought return period and the mean annual deficit (Ep-Pa), and between average drought return period and ratio of mean annual deficit to mean annual precipitation (Ep-Pa)/Pa.
The relationships between the Ep/Pa ratio and the percentage probability of occurrence of moderate, severe and extreme intensity droughts clearly show that the probability of occurrence of a severe or extreme intensity drought increases gradually from the semi-arid to the arid regions. However, it is reverse in the case of moderate intensity drought. Thus it is concluded that the areas located in arid regions are prone to suffer from relatively more intense meteorological droughts than the areas in semi-arid climatic region.
The occurrence of severe droughts is quite less in regions with Ep/Pa ratio less than 2. This again confirms that the climatic region with lesser mean annual deficit is less susceptible to intense droughts. The drought duration is seen to vary between 1 to 5 years in the different climatic regions. The median value of longest drought persistence among the different climatic regions is 2 years. However no relationship could be established between drought duration and Ep/Pa ratio.
The relationship presented in this report can be used as a useful tool for the prediction of regional drought characteristics and planning of appropriate drought management strategies for arid and semi-arid climatic regions of India.
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