RN-40 : Comprehensive review of drought indices

Abstract

Scores of drought definitions are available in the literature developed by a variety of disciplines because it affects so many economic and social sectors. Drought holds different connotations to different people. The phenomenon of drought can be interpreted in various ways depending on the scientific field involved, purpose and type of water use and extent to which it is perceived to be an expression of water deficiency. Accordingly, droughts are broadly categorised as meteorological, agricultural and hydrological droughts. A comprehensive review of important meteorological, agricultural and hydrological drought indices has been made to assess their applicability and limitations so as to select a particular criteria of drought quantification and help in developing improved drought indices.

The available drought indices vary from simple rainfall indices based on various threshold values to complex indices based on the water balance approach and soil moisture models. Most of the indices but for few comprehensive indices appear to be adhoc and work in isolation. They consider either rainfall alone or take some account of soil water storage and loss of water from soil storage by evapotranspiration. It is not sufficient to go by the variability of total rainfall alone but also to analyse and understand spatial and temporal variability in hydrologic process as well as study demand patterns to analyse drought in a better perspective. An overall water availability index could be a better index of drought.