Modeling climate change impacts on suspended and dissolved water quality constituents in watersheds

Abstract

The Hydrological Simulation Program-FORTRAN (HSPF) has been used to investigate the impacts of climate change on the water quality processes in hypothetical watersheds under different vegetation covers. A scenario has been constructed by extracting trends in temperature, precipitation, cloudiness, humidity and wind velocity using statistical methods from General Circulations Models (GCM) simulation results conducted by the Canadian Climate Center for a grid cell coinciding with western Turkey which is located in the Aegean and Mediterranean Region of the country. These trends have been used in creating daily values for meteorological time series utilized by HSPF as the driving force behind the hydrological and water quality processes. The scenario is based on the Special Report on Emission Scenarios (SRES) A2 scenario of the Intergovernmental Panel of Climate Change (IPCC). The four types of watersheds investigated are a barren watershed, a pasture, a watershed covered with coniferous forest and one with a deciduous forest. Sediment transport has been modeled and the quality of water in terms of conservative contaminants like chloride leaving the watershed as surface-runoff, interflow and groundwater outflow has been chosen as the variable to be investigated on a monthly basis as computed from daily simulation results. Simulations have been conducted for a time period of 47 years from 2004. Differences between scenarios have been observed in sediment transport and dissolved water quality variables affecting the sustainability of the use of the watershed for various purposes. The results can be used by watershed managers in planning the future use of watersheds and in determining the distribution of different vegetation types in rural watersheds. It is also demonstrated that HSPF is a powerful tool in the simulation of the effects of climate change on the hydrological and water quality processes of watersheds.