Rainfall-runoff events in a middle mountain catchment of Nepal

SummaryThe generation of runoff and the associated processes are important for the understanding of flood generation and sediment mobilisation. However, only few studies of this kind were conducted in the Hindu Kush-Himalayan region. This paper presents detailed rainfall event analyses in the Jhikhu Khola catchment in the middle mountains of Nepal’s Himalayas followed by analysis of runoff events in erosion plots on different land use.It shows that rainfall events in the catchment can be divided into four clusters: minor events, medium events, high intensity events and large events with each cluster having particular characteristics. Annually about nine high intensity events occur, most of them during the monsoon season. Large events, about one event per year, generally occur during the monsoon and the post-monsoon season. Both the high intensity and the large events are potentially important for the generation of floods in the catchment and beyond. Runoff events in the catchment are closely correlated to the event rainfall intensity parameters and the proposed clusters. Depending on land use another surface flow process is expected. While on degraded land infiltration excess flow is the key process in terms of runoff generation, on agricultural land saturation excess overland flow is more relevant. The bulk of the runoff is generated in a few major rainfall events. Particularly on agricultural land only few events cause the total annual runoff.