Spatio-temporal trends in observed and downscaled precipitation over Ganga Basin

Abstract. This paper focuses on the spatio-temporal trends of precipitation over the Ganga Basin in India for over 2 centuries. Trends in precipitation amounts are detected using observed data for historical period in 20th century and using downscaled precipitation data from 37 GCMs for 21st century. The ranking of 37 GCMs (from CMIP5 archive) is done employing a statistics based skill score. The best ranked GCM output is then bias corrected with observed precipitation prior to further analysis. The direction and magnitude of trend in annual and seasonal precipitation series is determined using Mann Kendall’s test statistic (ZMK) and Thiel Sen’s Slope estimator (β). The plots depicting the spatial variation of ZMK and β are prepared which provides a comprehensive inter-scenario comparison of spatio-temporal trends in precipitation series. Highly non-uniform spatio-temporal trends are detected for observed precipitation series. It is observed that the precipitation for annual and southwest monsoon season is indicating a rising trend for all future emission scenarios in the region adjacent to Himalayas (northeast side of study area) but shows falling trends in the plains away from the Himalayas. Insignificant trends are observed in pre-monsoon and winter season precipitation. An inter-emission-scenario comparison shows that for higher emission scenarios the annual and southwest monsoon precipitation is showing rising trends with increasing spatial dominance i.e. the area under rising trends increases as we observe it from low to high emission scenarios.