Spatio-temporal analysis of rainfall, meteorological drought and response from a water supply reservoir in the megacity of Chennai, India

Abstract

Abstract Assessment of rainfall variability and drought is essential to address the existing water crisis and water resources management. This study was carried out to assess the rainfall variability, meteorological drought and relative response of a water supply reservoir located in Chennai Metropolitan, India. Spatial and temporal variation of rainfall and drought across the river basin was assessed using historical rainfall records from 1978 to 2016. A significant number of rainfall stations show increasing trends in post-monsoon and northeast monsoon. The annual rainfall is concentrated for less than six months and shows an irregular to strongly irregular distribution. The degree of variability in monthly rainfall reveals markedly seasonal with long dry periods. Three different drought indices such as rainfall deviation method, Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) were used and compared to identify the meteorological droughts. The duration of meteorological drought events in this region ranged from 3 to 9 months. Identified drought events reveal that the rainfall deficiency in the northeast monsoon causes most of the meteorological drought. The reservoir system has higher response and coherence with SPI at a higher time scale. So, SPI can be used to represent the hydrological drought in higher time scales. Hence, SPI is recommended as more appropriate for drought assessments for this region. The large scale atmospheric circulations have moderate impacts on drought events in this region. The outcomes of this study could be useful for better drought and water resources management. Research Highlights Chennai region has higher interannual rainfall variability and susceptible to droughts once in about four years. About 44.44% of droughts in this region when India witnessed drought indicating large scale atmospheric circulations. Deficiency in rainfall during both southwest and northeast monsoon increase the gap between water demand and supply.