资源环境科技发展态势分析平台

This study investigated a detailed picture of some statistical properties of winter rainfall on monthly and seasonal basis over the Western Himalaya (WH) using rain gauge station data during 1902-2005. Results showed a significant shift in the rainfall and rainy-day pattern during 1960-1970 in most of the stations over the WH. State-wise analysis indicated that Himachal Pradesh has received more rainfall (50%) and rainy day (similar to 57%) compared to the state of Uttarakhand. Station data revealed that past winter rainfall has changed in a periodic manner with averaged periodicity (epoch) of 20 years in which 1920-1940 was characterized by excess rainfall period while 1970-1990 was depicted as deficient rainfall period. Most of the rain gauge stations showed declining trends of rainfall and rainy days while the intensity of rainfall indicated increasing trends during the 1902-2005 period. Regional-averaged winter rainfall and rainy day have shown a significant declining trend during 1902-2005. It was found that the rainfall trends are mainly arising due to internal variability although short-term trends (signal) override the internal variability (noise) in some cases. Among five goodness-of-fit distribution, the generalized extreme value (GEV) has emerged as the best fit for the majority of the station locations. Estimated monthly assured rainfall at 75% probability level revealed a range of 100-150 mm, which will be useful for agricultural activities over WH region. The impact of topography on rainfall and rainy day indicated increasing trends up to a certain elevation (similar to 1356 m), thereafter they showed decreasing trends that has been described through a second-order polynomial fit.