Scenario-based modeling of water yield under future climate conditions using the InVEST model (Jajrud watershed, Iran)

Document Type : Research Paper

Authors

1 Department of Civil Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.

2 School of Environment, College of Engineering, University of Tehran, Tehran, Iran

10.22069/ijerr.2026.24129.1575

Abstract

The increasing intensity of climate change and the accelerated urban expansion of cities in recent years have posed significant challenges to water resources in semi-arid regions such as the Jajroud watershed, located east of Tehran. This study applies a two-stage framework to assess the impact of future climate change on the basin’s water yield. In the first stage, historical and future climate conditions were examined using observational data and the results of the CMIP6 General Circulation Models (GCMs). The LARS-WG model was used for downscaling and bias correction, and the MRI-ESM2-0 model was selected as the best-performing GCM based on statistical criteria. In the second phase, the Water Yield model from the InVEST suite was used to estimate the spatial distribution of water yield under present (2024) and future (2040) conditions, using climate projections under scenarios SSP2-4.5 and SSP5-8.5. Model inputs included precipitation, reference evapotranspiration (ET₀), root-limiting depth, plant-available water, land use/cover, and a GIS-based biophysical table. Results indicate that water yield increased from approximately 80 MCM in 2014 to about 110 MCM in 2024, mainly due to higher recent precipitation. However, future projections reveal a strong decline, with total water yield decreasing to about 60 MCM under SSP2-4.5 and further dropping to 44 MCM under SSP5-8.5 by 2040, representing nearly a 60% reduction compared with current conditions. Besides climatic drivers, land-use changes—especially expansion of built-up areas and reduction of vegetation cover—further intensify water loss by limiting infiltration and increasing evaporation.

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Environmental Resources Research
Volume 14, Issue 1
January 2026
Pages 163-174

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