Juerg Merz

Potential Solutions to Water Scarcity in the Rural Watersheds of Nepal's Middle Mountains

Abstract Water scarcity is a major issue in rural watersheds in the Middle Mountains of Nepal and in the entire Hindu Kush–Himalaya region. Dense population and heavy dependence on irrigated agriculture place immense pressure on available water resources, which have a distinct seasonality. New forms of management based on traditional and scientific knowledge must be introduced to solve problems of water supply, water demand, and water quality in these watersheds. A related article in the Research section of this issue, Water: A Scarce Resource in Rural Watersheds of Nepals Middle Mountains, by Juerg Merz et al, further explores the problem of water availability in Nepal. Ed.

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

Abstract 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.

Measurement and distribution of runoff and soil losses from selected watersheds in the Hindu-Kush Himalayan region

The sediment loads of Himalayan Rivers are amongst the highest in the world, resulting in problems such as siltation of reservoirs, blockage of river channels and poor quality of water supplies. The aim of the study was to develop total sediment calculation and distribution on different land uses and thus to provide information for planning the quantification of sediment loads to rivers and reservoirs. Hydrological, meteorological and soil erosion data were collected from four watersheds, the Jhikhu Khola, the Hilkot, the Bhetagad and the Xizhuang, all of which featured several types of land use. Runoff and sediment losses were monitored. Total annual rainfall in the region ranged between 972 to 2400 mm. About 44 to 66 percent of rainfall occurred from June to August, which is mostly the Monsoon season in the region. Results show that runoff and soil losses were higher in the months of May to September, when rainfall duration and intensity were higher in all the watersheds. Large rainfall events contributed most of annual runoff and soil loss in the area. The highest annual runoff was generated in the Jhikhu Khola watershed under all conditions of land use while it was very low in the Bhetagan and Hilkot watersheds. The highest runoff and soil loss was recorded from degraded land plots because there less vegetation was available and the soil was loose and susceptible to erosion. In agricultural plots runoff and soil erosion was higher during the periods when there was no crop canopy and soil was not compacted after ploughing. During the months when crop cover was good there was less runoff and soil erosion. In pasture and forest plots runoff and soil loss was minimal throughout because of good vegetation and higher concentrations of organic matter that increased water infiltration and reduced runoff and soil loss.

Water Management Issues in Middle Mountain Catchments of the Nepal Himalayas: The Downstream Perspective

Middle mountain catchments in the Hindu Kush-Himalayan region are the heavily populated and mainly rainfed headwaters of many smaller, but not less important rivers, and the tributaries of the larger North-South rivers draining the mountain system. The catchments are in a fragile and vulnerable region from the perspective of water scarcity, flooding and soil erosion. It is these catchments which caused the theory of the ”Himalayan Environmental Degradation” (Eckholm, 1976).

Water accounting in two rural meso‐scale catchments of the middle mountains in Nepal

Abstract: This study assesses water needs and uses in two middle mountain catchments in Nepal, the Jhikhu Khola and the Yarsha Khola. It concludes that the amount of annual water available is adequate for the current water demands, and that rainwater stored to use it during the dry season can be useful to increase cropping intensity and change cropping patterns, if efficient irrigation methods are applied.