Hydrologic Impact of Climate Change on Planned Hydro Dams in Swat River Basin

In Pakistan, there exists already a rather high awareness on the threats that climate change might pose on water resources. Khyber Pakhtunkhwa province of Pakistan in particular Swat basin has experienced several disastrous floods during recent past. There is large potential of hydropower development in the basin and many projects are planned to be constructed in the coming years. Mohmand Dam, largest multipurpose storage dam in Swat basin is being constructed in the basin. Therefore, it is pertinent to investigate the impact of climate change in this basin. A hydrological model Soil and Water Assessment Tool (SWAT) is coupled with regional circulation models (RCMs) to assess the potential water resources and other water budget components of the future under the changing climate. The hydrologic model was calibrated and validated against the measured stream flow data using observed weather data and inputs from the global SWAT database. The SWAT and RCM performed well, especially on an annual basis. Climate change impacts on hydrology were then quantified by driving SWAT with the existing and future climate scenarios. The outcome of the research indicates that it is very likely that temperature will increase further in the future. It will result in early snow melt and peak flow pattern of the basin will shift from summer months to spring season. The modelling results reveal that overall increase in temperature will be about 1.32.2 degrees C and 2.3-3.75 degrees C in the century (2011-2099) under RCP 4.5 and RCP 8.5 respectively. The future projections also indicate that it is very likely that precipitation in the future will also vary with respect to baseline, the expected change in the precipitation will vary from 16% to 23% and -20% to 13.8% for the RCP 4.5 and RCP 8.5 respectively. The change in temperature, shift of snow melt season and precipitation will impact on the flow pattern of the basin and it is very likely that overall flow in the basin (Swat basin) will be more in the future. There will be more flows in the river from November to May and decrease in flows from June to December compared to existing scenario. The change in future precipitation simulated by the RCM produced 18% increase in & face runoff, and 24% decrease in base flow and 20% increase in evapotranspiration in the river (Swat Basin) on an annual basis.