Seasonal and annual rainfall trends in himachal pradesh during 1951-2005

Abstract

In this study, we have analysed seasonal and annual trends in rainfall and rainy days over Himachal Pradesh, an Indian state located in Western Himalayas. Based upon rainfall data of 37 stations for the period 1951-2005, it is found that the contribution of monsoon rainfall for the lower southwest part of the state is in the range of 60 to 80% of the annual total, while it is only around 35% for the higher elevation stations in the northern parts of the state. State averaged rainfall is decreasing significantly at 95% level for January (-0.61 mm/year), July (-1.83 mm/year), August (-.49 mm/year) and October (-0.90 mm/year). On seasonal scale, rainfall and rainy days are showing significantly decreasing trends for monsoon (-3.68 mm/year and-0.09 days/year respectively) and post monsoon (-0.98 mm/year and-0.03 days/year respectively). Annual rainfall and rainy days are showing significantly decreasing trends by-4.58 mm/year and-0.13 days/year respectively. Spatial patterns of monsoon rainfall and rainy days indicate significant decrease in southern and eastern parts of Himachal Pradesh, particularly in the Shivaliks and the middle Himalayas. Stations showing significant increasing trends in summer rainfall and rainy days are spatially coherent in the Shivaliks and the middle Himalaya. Seasonal rainfall is showing significantly increasing trend in winter (+1.47 mm/year) and summer (+1.77 mm/year) and significantly decreasing trend in monsoon (-3.71 mm/year) for Shimla, the capital of Himachal Pradesh. The daily heaviest rainfall is showing significantly decreasing trends in the southern parts of Himachal Pradesh (Hamirpur, Kotkhai, Nahan, Nurpur, Renuka (Rainka) and Pachhad. Stations showing significant increasing trends in annual daily heaviest rainfall are located in middle Himalayas [Chini (Kalpa) and Palampur]. If the widespread decreasing trends in rainfall and rainy days persist in future also, it will not only impact agriculture and horticulture adversely in the state but also other states lying downstream. However, this analysis will contribute to the knowledge of rainfall variability and trends over Himachal Pradesh and help agricultural, horticultural and water resources planners in decision-making in this important Western Himalayan state.