Effects of dynamic land use/land cover change on water resources and sediment yield in the Anzali wetland catchment, Gilan, Iran.

Land use/land cover (LULC) changes strongly affect catchment hydrology and sediment yields. The current study aims at analyzing the hydrological consequences of dynamic LULC changes in the Anzali wetland catchment, Iran. The Soil and Water Assessment Tool (SWAT 2012) model was used to assess impacts on evapotranspiration, water yield, and sediment yield. Two model runs were performed using static and dynamic LULC inputs to evaluate the effects of LULC change between 1990 and 2013. For the static model, the LULC map of 1990 was used, whereas for the dynamic model, a gradual change of the LULC distribution was interpolated from 1990, 2000, and 2013 LULC data. The major LULC changes were identified as an increase of agricultural area by 7% of the catchment area and a decrease of forest coverage by 6.8% between 1990 and 2013. At the catchment scale, the differences in the long-term mean annual values for the main water balance components and sediment yield were smaller than 10 mm (<2.8%) and 3 t/km (<2.6%), respectively. However, at the sub-basin scale the increase of agricultural land use resulted in an increase of evapotranspiration, water yield, and sediment yield by up to 8.3%, 7%, and 169%, respectively, whereas urban expansion led to a decrease of evapotranspiration, water yield, and sediment yield by up to -3.5%, -2.3%, and -9.4%. According to the results of the monthly time scale analysis, the most significant impact of LULC changes occurs during the dry season months, when the increase of irrigation agriculture results in an increase in water discharge and sediment loads to the Anzali wetland. Overall, the results showed that the implementation of dynamic LULC change into the SWAT model could be adopted as a planning tool to manage LULC change of the Anzali wetland catchment in the future.