Analysis of climatic variability and its response to streamflow of Langtang River basin of Nepal.

Abstract:

The Himalayas display great climatic variability which has greatly affected the water resource availability. Climate change is expected to contribute to increased variability of river runoff due to changes in the climatic variables as well as the melting of snow glaciers. Therefore, it is essential to understand the underpinnings of hydro-climatic variability in order to assess the effects of climate changes. This study therefore provides the analysis of observed variability and change in temperature, precipitation, snow cover and its response to streamflow of Langtang River Basin of Nepal. Langtang River basin which lies in Langtang Valley of Rasuwa district is glacier-fed and provides sustained flow during dry seasons to fulfill the water requirements for downstream.The observed hydro-meteorological data for the period 1988 to 2009 was used for this study.

Trend analysis of temperature data using non parametric Mann-Kendall test revealed that there is increasing trend of temperature and was more pronounced in winter season (December, January, February). Also observation shows that the total number of days per year below 0^oC has been decreasing. Similarly, total annual precipitation showed increasing trend but have large interannual variation. Pre monsoon, post monsoon and winter precipitation also showed increasing trend whereas the monsoon precipitation was observed to have decreasing trend. Monsoon precipitation in the region amounts 84.78% of total annual precipitation. Snow cover area (2002-2014) examined using the data acquired from MODIS snow data showed decreasing trend. Seasonal variation in the snow cover with two peaks in most of the years is observed. This variation is explained by temporal variation of temperature and precipitation. The annual stream flow showed decreasing trend. The streamflow at monsoon and post monsoon seasons were found to be decreasing and winter and pre monsoon streamflow showed increasing trend. The streamflow was observed to start increasing in June and reach peak in July and August. In the post-monsoon period and winter, snowmelt contribution to the total discharge is large. This study would be useful in understanding how the hydrological regime has been changing with climate change in mountainous watershed and would be helpful for water resources management.