recent trends in the onset and withdrawal of summer monsoon over nepal

this paper presents the analysis of the onset and withdrawal dates and the duration of summer monsoon over nepal for last 63 years (1951-2013). the trend analysis revealed that both the onset and withdrawal of summer monsoon are delayed in recent years. the statistical analysis using cumulative deviation and worsley likelihood tests showed a step jump in mean withdrawal date after the year 1997. the mean withdrawal date after 1997 is later than the normal withdrawal date by 10 days. although, the trend for onset is statistically insignificant, the trend for withdrawal is significant at 5% level. stationarity tests for the period of 1951-1996 and 1997-2013 also revealed that both the onset and withdrawal series are non-stationary. a step change in withdrawal date with delayed trend on both onset and withdrawal coupled with longer duration suggests a temporal shift in the monsoon pattern over nepal after 1997. the temporal shift in the monsoon is consistent with published findings on the effect of global climate change on the dynamics of the south asian summer monsoon precipitation. the shifting pattern of the summer monsoon exerts a strong stress on agriculture, water resources, ecosystems, human health and the overall economy of the country.