ANALYSIS OF CLIMATE CHANGE IMPACTS IN MARSHYANGDI RIVER BASIN, NEPAL

Abstract

Climate change is impacting Nepal’s economy, health and communities in diverse ways. Rising temperatures are responsible for the glacier melt as well as shift in precipitation pattern. Changes in the climatology of precipitation lead also to changes in runoff and streamflow. The other effects include increase in the prevalence of severe events like floods and drought along with erratic rainfalls. The present study analysed the change in climatic condition i.e. on Precipitation and Temperature in Marshyangdi River Basin (MRB) and its impact on the streamflow. Observed streamflow data is available from 2000-2009 for a duration of 10 years at Bakhundebesi station, outlet of the MRB. Hydrological modelling was used to construct streamflow series of about 30 years’ at Bakhundebesi station to perform a trend analysis in order to study the impact of climate change. Hydrological modelling was attempted to construct the streamflow series of around 30 years. Soil Water Assessment Tool (SWAT) model was calibrated and validated with SWAT Cup program using SUFI2 algorithm. During calibration period, values of Nash-Sutcliffe Efficiency (NSE), Percentage Bias (PBIAS) and Coefficient of Determination (r2) were found to be 0.75, 12.64 and 0.77 respectively for daily data. Similarly, for monthly data these parameters were estimated to be 0.84, 12.21 and 0.89. During validation phase NSE, PBIAS and r2 were estimated to be 0.69, 10.21 and 0.70 for daily data and 0.84, 10.10 and 0.86 for monthly data. At the end, streamflows were generated from 1977, the year where from the observed precipitation data was available. Climate change impacts analysis was carried out through trend analysis of meteorological parameters viz: precipitation, minimum and maximum temperature. Mann-Kendall (MK) and Sen's slope estimator test were used. Maximum temperature is showing significant increasing trend in the basin at both the stations and in all seasons. At Khudibazar station minimum temperature is also showing significant increasing trend while at Chame station in minimum temperature series no significant trend is observed. In precipitation series no significant trend is observed in any season in the basin, with varying changes across the seasons. In the basin precipitation, -17.18% and -54.77% changes are observed in pre-monsoon and winter season while in monsoon and post-monsoon season 12.08% and 27.19% changes are observed in the basin, with a net increase of 5.07%. xi The trend analysis of streamflow was also performed and showed the increasing trend with the significant variation in the percentage change to the corresponding seasons. Trend analysis of annual streamflow determine a significant increasing trend in the basin with a 3.19% increase in mean annual flow comparing with the Basin average annual rainfall, these changes are attributed to 5.07% increase in rain fall during this period.