资源环境科技发展态势分析平台

We investigate trends in monsoon and extreme precipitation in Nepal based on rain gauge measurements. We find that precipitation amounts in Nepal vary considerably in space and time. The number of occurring extremes and the amount of precipitation are controlled mainly by the Indian summer monsoon. Almost all extreme precipitation events, recorded by 98 considered meteorological stations, occur during the Indian summer monsoon with the maximum in July. For Nepal in general, we find that the amount of precipitation and number of extreme events per station are neither significantly increasing nor decreasing between 1971 and 2010. However, on a regional scale we identify areas with positive and negative trends. A comparison of the combined precipitation time series with the ENSO 3.4 index reveals a connection between ENSO and the variability in monsoon precipitation. The correlation with the number of monsoon extremes vanishes for increasing percentiles. We investigate trends of upper percentiles of daily precipitation which pinpoint regions of increasing and decreasing extremes. These patterns are similar to spatial patterns in mean monsoon precipitation trends, whereas the median of the precipitation distribution undergoes only minor changes. Further analysis using extreme value theory confirm the prevailing trends from quantile regression for most stations and depict strong changes in return levels. Especially for Far-West Nepal, we find robust evidence for a systematic increase in extreme precipitation.