Rainfall amount and intensity in a rural catchment of the middle mountains, Nepal

Though rainfall intensity is the most important parameter for the investigation and prediction of flood generation and soil erosion, only limited information on this characteristic is available in the Nepal Himalaya. The People and Resources Dynamics of Mountain Watersheds in the Hindu Kush-Himalaya Project (PARDYP) is maintaining several high-density raingauge networks in mesoscale catchments of the Hindu Kush-Himalayan middle mountains. The first results from the network in the Jhikhu Khola catchment (JKC), where the longest data series is available, are presented here. In general, the catchment experiences monsoon type rainfall with about 78% of the annual rainfall occurring during the monsoon season. During the remainder of the year, rainfall is variable and erratic. The highest rainfall intensity occurs in the pre-monsoon season followed by the monsoon season and the same pattern is observed in the case of the erosivity. About 90% of the total annual rainfall has the potential to contribute to runoff generation and about 87% contributes towards sediment mobilization. Spatially, there is no distinct difference between the rainfall event parameters visible during the events, which cause the largest flood events at the outlet of the catchment. Rainfall in the lower lying JKC is generally lower. For extrapolation of the intensity information the intensity-duration-frequency (IDF) relationships were calculated. It is showed that the IDFs used to date heavily underestimate the short-duration intensities and their recurrence.