Will the Bagmati Basin’s Future Hydrological Change be linked with Global Climate Change Patterns?

The impact of climate change on society is one of the most serious challenges of this century. Observations have shown that the Earth’s hydrologic cycle has intensified during past century as the Earth’s temperatures have increased. Such change in hydrology will affect nearly every aspect of human well being, from agricultural productivity and energy use to flood control as well as municipal and industrial water supply. This study therefore, focuses on using climate projection data (precipitation and temperature) from an ensemble of 16 Global Climate Models (GCMs) and Thornthwaite Monthly Water Balance Model (TMWB) to assess changes in the basin hydrology in a high altitude mountainous Bagmati basin of Nepal. This region is considered as one of the most disaster (landslides and flood) prone basins in Hind-Kush-Himalaya due to the summer monsoon. The assessments were conducted for short (2020-2029), medium (2060-2069) and long (2090-2099) terms relative to the base period of the 1990-1999 in high (A2), medium (A1B) and low (B1) emission scenarios. According to GCMs the basin is expected to witness higher temperatures from about 2ºC (B1) to 4.5ºC (A2) and receive higher precipitation from about 7% (B1) to 20% (A2) in 2099. The increased precipitation is primarily expected to occur during the monsoon season, suggesting a wetter monsoon. The results from TMWB modeling show generation of higher runoff, especially during the wet monsoon season, compared to 1990-1999. This implies that the basin will most likely become more vulnerable to floods and landslides during future monsoon seasons.