AbstractHuman interventions and climate change have caused significant alterations in the hydrologic response of several highly managed basins in Iran. One of these alterations is a considerable reduction in streamflow quantity, resulting in severe water supply insecurity. This paper presents an integrated modeling approach combining remote sensing, water balance analysis, reservoir operations, and water allocation policy evaluations. The approach helps in understanding of the relative contribution of anthropogenic factors in places where a major challenge is the lack of measured data for the historical time series of water withdrawals for agricultural development and water lost from the system through actual evapotranspiration (AET). Calibrated moderate-resolution imaging spectroradiometer (MODIS) remote sensing data of monthly AET (MOD16), modified Thornthwaite-Mather (M-TWM) water balance model, annual MODIS Land Cover Type (MCD12Q1) products (MCQD12Q1), mass curve analyses, and periodic analysis of water balance parameters were used to evaluate the contribution of anthropogenic factors and the effect of climatic impacts on the inflow time series for the Talvar Reservoir. The procedure led to an estimation of the naturalized series of the streamflow free of anthropogenic impacts; based on this, more plausible estimates of the basin’s future water availability were determined, which were then used in a water evaluation and planning (WEAP) model for Talvar Reservoir operations and water allocations. The study yielded four main results. First, it was seen that there were two abrupt change points in the analyzed mass curves, in the years 1998 and 2007, dividing the study period (1988–2012) into three periods. Periodic analysis of water balance parameters showed that while climate change caused streamflow changes in postimpact period A (1998–2007), intensified human activities brought about streamflow changes in postimpact period B (2008–2012). Secondly, it was found that the naturalized series of the Talvar streamflow had a better correlation coefficient with precipitation than the observed series for river flow. Thirdly, despite the proposed approach lacking the use of some water balance components such as soil moisture and snow water equivalent, the percentage of unaccounted water content was between 5% and 10%, indicating good accuracy of the proposed approach as a tool for sustainable water resources management. Fourth, the WEAP model simulation results demonstrated that the unfavorable condition of the aquifer can be ameliorated by applying proper management policies. The results also showed that to increase water supply security and facilitate sustainability, a certain amount of reduction in ground-water withdrawals and agricultural areas is inevitable.