Assessment of Water yield service on the basis of InVEST tool (case study: Delichai watershed)

  Numerous benefits that people obtain from ecosystems are called ecosystem services. This services have a wide range and one of the most valuable of them is water Yield. Water Yield means long-term average of annual rivers flow and recharge of aquifers by precipitation. In these years, due to different land use types and their potential in water yield, the evaluation of water yield at each land use type is important. The objective of this study is to assess and map the water yield at different land uses such as rangeland, agriculture, built up area, bare ground and Juniperus ecological niche to decide which management decisions are appropriate for the area and how much water is provided by each land use. this study is done in Delichai watershed, one of the northern sub watersheds of Hableroud river basin that located in Tehran province. The water yield model is based on the Budyko curve that determines the amount of water running off each pixel of land as the total precipitation less the fraction of the water that undergoes evapo-transpiration. the required data include maps of land use and land cover, annual precipitation, average annual potential evapotranspiration, soil depth, plant available water content, boundary of watersheds and sub-watersheds as well as a biophysical table reflecting the biophysical attributes that entered in InVEST 3.3.2 tool to map and estimate water yield ecosystem service. After entering the required data model as well as compare the initial results obtained with the actual data in the outlet, model calibrated with hydrogeological parameters Z, and the final results were obtained after calibration. According to the results, the amount of water runoff in whole Delichaee watershed is about 42 million cubic meters. Results in different land uses indicate that the maximum amount of runoff in land uses is in bare grounds with 2923.992 cubic meter per hectare and then, Rangeland and agriculture land uses with 1264.109 and 1062.725 cubic meter per hectare runoff respectively have the highest values. Also, the lowest amount of runoff is 511.287 cubic meter per hectare in Juniperus ecological niche. Results of this study shows that Although InVEST model needs available and relatively simple data but it has high efficiency. And we can use it for mapping ecosystem services and decision making. Physiographic and climatic factors have a great impact on the amount of water in watershed and among these factors, elevation and precipitation are the most effective ones also we should not overlook the effect of vegetation. Therefore according to importance of water provision and problems in water supply for people who live in the region using this model or other models like it, we can estimate the relative runoff and the role of vegetation in reducing it.