Application of the LISEM Soil Erosion Model to a Forested Catchment in the Indian Himalayas.

The Himalayan region is an ecologically fragile region, in which degradation of the environment is a serious threat. Degradation and hydrology are linked, since rainfall and runoff influence erosion, and soil moisture content influences ecosystems and plant growth. Thus, it is important to get insight into the hydrological system in order to combat degradation. Rainfall and soil moisture content were measured in the 12 km2 Arnigad catchment, Uttarakhand State, India. Measurements of rainfall were done with tipping bucket rain gauges, at five locations in the catchment, and soil moisture was measured at different depths in dense oak forest and degraded forest inside the catchment using automatic sensors. Runoff from the catchment was measured at the catchment outlet using a capacitive water level sensor. The measurement period included three monsoon seasons (2003-2005). For these seasons, monsoon rainfall of 2186, 2033 and 1386 mm was recorded respectively. It was found that there were no clear relationships between rainfall amount and position in the catchment, but the rain gauge at the highest elevation was found to deviate from the others and recorded less rainfall. Soil moisture content showed clear reactions to rainfall up to at least 25 cm soil depth. Soil moisture content was found to be fairly constant during the monsoon season, suggesting that the soil became saturated with water in early showers of the monsoon. During the monsoon season, soil water content increased by no more than 5% as a result of rainfall events, resulting in discharge during rains. Runoff data suggested that during the monsoon season, rains with more than about 12 mm of rainfall, or peak intensities of more than 30 mm h-1, produced runoff from the catchment. Since direct runoff represented, on average, only 3% of rainfall, the data suggest that a large part of rainfall quickly infiltrates to greater depth, where is becomes throughflow or baseflow.