SPATIAL AND TEMPORAL ASSESSMENT OF DROUGHT IN THE KRISHNA RIVER BASIN

Abstract

Drought is a significant natural hazard that affects the society and economy in the most deteriorating manner compared to other natural disasters. The occurrence of drought is generally correlated to the deficiency in precipitation, soil moisture depletion, depleting surface and subsurface water levels. Duration of drought may vary from few days to several years. Deficiency of rainfall marks the starting of meteorological drought. Further intensification of meteorological drought leads to agricultural and hydrological droughts. Drought is hard to define in terms of its onset, extent and termination and is said to affect a large part of the population of the region in which it spreads. Also, drought occurrences have become frequent in large parts of the world and hence the need of drought research is imperative. Drought can be evaluated by various physical drought characteristics using drought indices. Also, the risk of drought in a region is computed through drought hazard and vulnerability indices using various socio economic variables since the society and economy of a region governs the effect of a natural disaster. In the present study, drought characterization for Krishna Basin, a drought prone river basin in southern part of India has been undertaken. Physical characterization of meteorological drought has been studies using commonly used meteorological drought indices. Based on these drought characteristics, Drought Hazard Index has been calculated. Using the various socioeconomic variables, Drought Vulnerability Index has also been calculated for the basin. Using DHI and DVI, Drought Risk Index has been obtained. Spatial analysis of drought characteristics and hazard, vulnerability and risk has been performed and spatial maps for the same have been generated using ArcGIS software to understand the spatial variation of drought. The methodologies applied and major findings from the study are summarized below. PHYSICAL DROUGHT CHARACTERIZATION Drought characterization is done by the use of various meteorological drought indices. In this study we have used Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Effective Precipitation Evapotranspiration Index (SP*ETI) and Reconnaissance Drought Index (RDI) to physically characterize the past droughts of the Krishna Basin in terms of maximum drought magnitude, maximum drought duration and iii frequency of drought occurrence. It was found out that the districts having a high drought magnitude also had longer drought duration. The frequency of occurrence of moderate droughts was the highest, followed by severe droughts and then extreme drought events for all the districts of the basin. The maximum drought duration was higher for RDI and SPEI when compared to SPI and SP*ETI which could be attributed to consideration evapotranspiration at potential rate both by RDI and SPEI indices. SPATIAL ANALYSIS OF AVERAGE MAGNITUDE, DURATION AND INTENSITY Spatial maps for various drought characteristics for the most severe drought years of the past have been prepared for three drought years namely 1918, 1972 and 1984. Spatial variation of average drought magnitude, duration and intensity for all the four indices during these dry periods were plotted on maps using ArcGIS software. It was found out that the indices behaved in a similar manner for each drought year with few discrepancies observed for RDI index due to a low coefficient of correlation that was observed for it. ANALYSIS OF DROUGHT HAZARD, VULNERABILITY AND RISK INDICES Drought Hazard Index (DHI) was calculated using the four physical drought characteristics. Socio economic variables were used to evaluate Drought Vulnerability Index (DVI). Drought Risk Index (DRI) was computed as a product of DHI and DVI. Spatial maps for DHI and DRI were obtained for all the four indices while a single DVI map was obtained for the basin. It was found out that districts showing high drought intensity did not compulsorily show a high risk. This could be attributed to the socio economic sensitivity persisting in those districts