DEVELOPMENT OF DROUGHT INDICES FOR KERALA

Funding Agency: Kerala State Council for Science, Technology and Environment

The definition of drought is quite tricky in the sense that, although it occurs almost everywhere, its characteristics such as severity and duration vary from one location to another. A simplistic and general approach is to look at the shortage of water availability to meet the demands for any or all use sectors. In that context, the terms ‘drought’ and ‘drought prone area’ (or region) may be misnomers, and need to be scientifically defined. At the National level, the State of Kerala has always been sidelined on the premise that it is a high rainfall area with adequate and even excess water resources. On the surface, the State’s unique humid tropical climate, heavy monsoon rainfall, lush greenery and the existence of a vast network of backwaters and wetlands naturally give the impression that it is a water surplus State. However, the adverse impact of inadequate water availability is as severe in Kerala as in other parts of the country, though it may not be as obvious. The steep terrain and the shallow and well–drained soil cover permit quick removal of the heavy rains that fall on the land, unlike in the rest of the country. Recognizing this, a one–year study was undertaken on the development of ‘Drought Indices for Kerala’.

While floods are the result of one end of the extremes of the meteorological spectrum, and are measurable, definable, and to an extent even predictable, droughts occur at the other extreme, are not readily quantifiable, involve a wide band of time scales, even as much as several years, and are more difficult to define. Estimating the intensity or severity of droughts as well as the proper choice of time scales, are therefore very critical in the development of possible definitions of drought.

The study attempted to develop separate drought severity indices based on four aspects, namely, (i) meteorological - called Standardized Rainfall Indices (SRI), (ii) hydrological - Standardized Flow Indices (SFI), (iii) agricultural - Standardized Agricultural Indices (SAI) and (iv) hydel energy - Standardized Energy Indices (SEI), for the unique humid tropical conditions that exists in Kerala. An attempt was also made to combine the four index series using judiciously selected weightage factors, but without resorting to serious scientific analysis on weightages.

The value and advantages of a well-documented, scientific, non-dimensional and standardized drought severity index cannot be over-emphasized. This seems to be best, if not the only way drought severity for any period and for any location can be compared in a rational manner, be it for Kerala, Rajastan, Punjab or Meghalaya. It is necessary to develop such indices for all States/regions in the country and operationalise them for triggering drought relief operations in an equitable and rational manner at the National level.