Implications of climate-driven variability on some ecological issues of headwater watershed system in mountain regions

Background/Question/Methods

Mountains have complex topography that cause variations in precipitation and hydro-glaciological regimes. As mountain watersheds are repositories of water and biodiversity, it is crucial to understand the ecological and hydrological complexities of these habitats. Headwater streams are likely to be highly sensitive to the effects of climate change and water characters are basically depend on changing pattern of precipitation and melting of snow and ice. The major objective of this study was to assess potential changes associated with watershed and stream processes under future climate change scenarios. For this study, we used Soil and Water Assessment Tool (SWAT 2009) to simulate the hydrologic discharge, sediment and nutrients loading from Narayani River Basin Watershed, Nepal, in the Himalayan Mountains utilizing low, medium and high emission scenarios predicted by general circulation models for 2050.

Results/Conclusions

 We calibrated the model using seven years historic discharge data and found good agreement between observed and model predicted values with r² as 0.79. During calibration, we found that the precipitation lapse rate, temperature lapse rate, and effective hydraulic conductivity in main channel alluvium as the most confounding factors to influence predicted river discharge. According to input landuse data, the watershed has 4% area covered by the permanent ice and contributing 22% to the discharge of associated river system and in contrast the snow contribution is by 8%; remaining 70% by rainfall. For the watershed, our simulation showed that potential evapotranspiration is increased by 4%, 6% and 5% in low, medium and high emission scenarios respectively but the plant biomass decreased in all scenarios. The discharge increased for all emission scenarios. Except for mineral phosphorus, concentration of most of other nutrients in streamwaters decreased. Dissolved oxygen in stream discharge increased by 7%, 2% and 2% as compared to current for each scenario respectively. Similarly, chlorophyll-a also increased for all scenarios. Our simulations showed that this watershed may significantly change in terms of terrestrial plant and aquatic primary production associated with water supply and seasonality of flow events.