Spatiotemporal variability of rainfall and its effect on hydrological regime in a tropical monsoon-dominated domain of Western Ghats, India

Study region: Kerala, Southern Western Ghats, India Study focus: A better understanding of the trends in rainfall, its distribution and characteristics is of paramount importance, for effective management of water resources, especially, in regions with marked spatiotemporal variability in rainfall. The present study examines the spatiotemporal changes in rainfall pattern and its effect on the hydrological regime of a tropical monsoon dominated region in Western Ghats, India. New hydrological insights for the region: Weakening of monsoon rains was observed in the region, with decreasing trend in monsoon season, increasing trend in pre-monsoon season as well as an accelerated change in rainfall pattern during the recent decades. Monsoon droughts are becoming more prominent as evidenced the increasing trend in total number of dry and prolonged dry spells. Seasonality Index of rainfall consistently showed decreasing trend indicating that the rainfall distribution is becoming more symmetric over the years. No significant relationship was observed between ENSO events and rainfall characteristics indicating that ENSO episodes do not considerably affect the variability of rainfall in the region. Effect of changes in rainfall characteristics have a strong bearing on the hydrological regime of the region, which was evident in the declining trend of streamflow and groundwater level. The study calls for a revised plan for water management, adaptive cropping pattern and reservoir operations in the state of Kerala.