Impact assessment of vegetation loss on the ecosystem functions in a semiarid watershed in Iran

The main purpose of this study is to investigate the effects of land cover changes and vegetation loss under conditions of change in climatic parameters (temperature and precipitation) and determining their impacts on different ecological functions in the eastern watershed of Lake Urmia and its four sub-watersheds in northwestern Iran. The method used has been a quantitative assessment of selected ecosystem functions using a self-parameterizing, physically based model called Water World Policy Support System as well as applying satellite images to detect land-use/cover changes. Modeling of important ecological and hydrological parameters including vegetation density, water balance, surface runoff, and soil erosion was performed and for each of them, the quantity of changes was calculated and mapped. Then, by standardizing the maps for each parameter and overlapping them, cumulative impact levels across the watershed were classified. The result showed that with decrease in rainfall and increase in temperature, the average vegetation density decreased by 32% in the watershed and from 79 to 47%. Decreased vegetation, followed by increased runoff by about 2.5% and equivalent to 19,656.95 cubic meters per year. Consequently, the average net soil erosion has been changed from - 0.012 to 0.20 mm per year per square meter. Hence, the average soil erosion in the watershed has increased by more than 3 tons per hectare. Based on the final results, more than 40% of the watershed area is under severe and very severe ecological impact.