Assessment of Spatio-temporal variability of climate in the lower Gangetic alluvial plain

Global climate change is a cause of concern as extreme events have intensified in recent years, with increased floods and droughts also reported in the Lower Gangetic Plain (LGP). Assessments from Regional Climatic Models (RCM) cannot capture the local climate variability necessary for devising an action plan for climate risk mitigation. The present study aims to fill this gap by assessing the long-term local-scale climate variability using Modified Mann-Kendall (MMK) and Centroidal Day (CD) shifts for the Patna district, which can be extended to other districts in the LGP. The time series is split into two halves to account for changes due to urbanization in recent three to four decades. CD analysis shows a forward shift in the monsoonal and annual rainfall in recent decades. The variability in total rainfall has become more pronounced post-1985 during monsoon, postmonsoon, and winter seasons. An increase of 64.53 mm (18.9%) in surface runoff and a strong correlation between built-up area and precipitation further cement the role of urbanization in local climate change. Despite a 5.74% decrease in monsoonal rainfall, a 3.51 mm/day increase in rainfall intensity is observed during the monsoon. The implications of these variabilities have posed new challenges for the agricultural production and management of water resources and the interactions between groundwater and surface runoff.