Spatio-Temporal Variability and Long-Term Trends of Rainfall in the Punpun River Basin, Bihar, India

Abstract

A good knowledge of long term variability of rainfall is essential for sustainable water resources planning, agricultural management and climate adaptation in monsoon dominated river basins. The Punpun River Basin, a large right bank tributary of the Ganga River in Bihar, India is extremely vulnerable to monsoon flooding and dry season water scarcity, and these extremes have further increased under changing climatic conditions. The present study has been undertaken to examine the spatial and temporal characteristics of rainfall over the Punpun River Basin using the long term daily rainfall data of eight rain gauge stations of India Meteorological Department (IMD) for the period 1981-2022 (42 Years). Variability is measured using statistical indicators such as mean rainfall, standard deviation, coefficient of variation (CV), rainfall anomaly index (RAI) and precipitation concentration index (PCI). The non-parametric Mann-Kendall (MK) test and Sen’s slope estimator are used for detection of monotonic trends and Modified Mann-Kendall (MMK) test is used to account for serial correlation in the data. Innovative Trend Analysis (ITA) and Sequential Mann–Kendal (SQMK) tests are used to determine hidden trend and abrupt change points in annual and seasonal rainfall series. GIS based ordinary kriging interpolation is used to map the spatial distribution and trend patterns. Results show a high spatial heterogeneity of the rainfall distribution with higher mean annual rainfall in the southeastern upland sector (~1,059mm) and lower values over the northern alluvial plains (~943mm). More than 86% of the annual rainfall is received during the southwest monsoon (June-September) and the PCI is >22 at all stations indicating strong rainfall seasonality. Significant decreasing trends were seen at Gaya (Z = -2.87, β = -4.12 mm/yr) and Aurangabad (Z = -2.31, β = 3.47 mm/yr) and significant increasing trend was observed at Arwal (Z = +2.54, β = +3.82 mm/yr). The SQMK test detects the change points around 1998-2000 in Gaya and 2002-2004 in Arwal. Gaya showed non-linear response with enhancement in low rainfall subcategories and Arwal showed a general wetting trend. These results provide scientific evidence for spatially differentiated flood management, drought mitigation, planning groundwater recharge and climate resilient water resources management in eastern India .