Abstract
The total phosphorus (TP) concentration, as the primary limiting eutrophication factor in the Mahabad Dam reservoir in Iran, was studied, considering the combined impacts of climate change, as well as the scenarios on changes in upstream TP loadings and downstream dam water allocations. Downscaled daily projected climate data were obtained from the Beijing Normal University Earth System Model (BNU-ESM) under moderate (RCP4.5) and extreme (RCP8.5) scenarios. These data were used as inputs of a calibrated Soil and Water Assessment Tool (SWAT) model of the watershed in order to determine the effects of climate change on runoff yields in the watershed from 2020 to 2050. The SWAT model was calibrated/validated using the SUFI-2 algorithm in the SWAT Calibration Uncertainties Program (SWAT-CUP). Moreover, to model TP concentration in the reservoir and to investigate the effects of upstream/downstream scenarios, along with forecasted climate-induced changes in streamflow and evaporation rates, the System Dynamics (SD) model was implemented. The scenarios covered a combination of changes in population, agricultural and livestock farming activities, industrialization, water conservation, and pollution control. Relative to the year 2011 in which the water quality data were available, the SD results showed the highest TP concentrations in the reservoir under scenarios in which the inflow to the reservoir had decreased, while the upstream TP loadings and downstream dam water allocations had increased (+29.9%). On the other hand, the lowest TP concentration was observed under scenarios in which upstream TP loadings and dam water allocations had decreased (−18.5%).
Highlights
Human activities have influenced the water quality in aquatic ecosystems by altering nutrient fluxes into receiving water bodies
The Beijing Normal University Earth System Model (BNU-Earth System Models (ESMs)) under RCP4.5 and RCP8.5 was implemented in order to obtain temperature, precipitation, and evaporation values for the period of 2020 to 2050
The outputs of the BNU-ESM under RCP4.5 and RCP8.5 were used as the input of the Soil and Water Assessment Tool (SWAT) model to simulate streamflow in the watershed during 2020 to 2050
Summary
Human activities have influenced the water quality in aquatic ecosystems by altering nutrient fluxes into receiving water bodies. The recent global warming is expected to affect nutrient loss dynamics in watersheds by changing atmospheric and meteorological properties, such as precipitation patterns, atmospheric water vapor, and evaporation This situation could make lakes and reservoirs more vulnerable to eutrophication [1,2,3]. Watershed-scale models were implemented to study the effects of climate change and land management practices on watershed yields. Du et al (2019) [14] implemented the SWAT model to study the impacts of different land use and climate change scenarios on the runoff yield of the Dagu River basin in China. Using an SD model, the authors studied the impact of climate change on water demand and the water supply from the Colorado River.
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