University of Applied Sciences and Technology of Tehran Municipality Urban Development Policy Making 3092-653X 3 2 2026 06 01 Climate Change Adaptation Policy in Tehran: Reinterpreting Spatial Precipitation Patterns over the Next 20-Year Climate Change Adaptation Policy in Tehran: Reinterpreting Spatial Precipitation Patterns over the Next 20-Year 201 211 242503 10.22034/judpm.2026.568604.1078 FA Mohammad Reza Farzaneh Assistant Prof. at Research Group of Environmental Engineering and Pollution Monitoring, Research Center for Environment and Sustainable Development, RCESD, Tehran, Iran Mohammad Abdolhosseini Assistant Professor, Water Engineering Department the Director of Educational Affairs, Gorgan University of Agricultural Sciences and Natural Resources (www.gau.ac.ir), Gorgan, Golestan Province, Iran Journal Article 2025 11 28 The development of the Tehran metropolis requires adherence to spatial planning and resource capacity, especially hydrological limits. This study analyzes the impacts of climate change on precipitation distribution in Sub-basin 4133, which affects Tehran's urban policymaking. Given limited high-altitude observational data, TerraClimate reanalysis data were validated (R^2 > 0.85). Precipitation patterns from the past 70 and 20 years were studied, and future changes under four Shared Socioeconomic Pathways (SSPs) were projected using the median of five CMIP6 models with the Change Factor downscaling method. Results show a "spatial contraction of high-precipitation zones" in the last 20 years, decreasing the basin's hydrological inflow. Future projections indicate an inevitable precipitation decline even under the sustainable scenario (SSP1-2.6), with the pessimistic scenario (SSP5-8.5) predicting a severe water resource collapse in northern highlands (below 190 mm). This, potentially worsened by Tehran's Urban Heat Island (UHI), could lead to destructive flash floods, reduced soil permeability, compromised groundwater recharge, and increased land subsidence in southern districts. The findings underscore the critical need for urban regeneration to implement the "Sponge City" model and update spatial planning documents according to the basin's revised ecological capacity. The development of the Tehran metropolis requires adherence to spatial planning and resource capacity, especially hydrological limits. This study analyzes the impacts of climate change on precipitation distribution in Sub-basin 4133, which affects Tehran's urban policymaking. Given limited high-altitude observational data, TerraClimate reanalysis data were validated (R^2 > 0.85). Precipitation patterns from the past 70 and 20 years were studied, and future changes under four Shared Socioeconomic Pathways (SSPs) were projected using the median of five CMIP6 models with the Change Factor downscaling method. Results show a "spatial contraction of high-precipitation zones" in the last 20 years, decreasing the basin's hydrological inflow. Future projections indicate an inevitable precipitation decline even under the sustainable scenario (SSP1-2.6), with the pessimistic scenario (SSP5-8.5) predicting a severe water resource collapse in northern highlands (below 190 mm). This, potentially worsened by Tehran's Urban Heat Island (UHI), could lead to destructive flash floods, reduced soil permeability, compromised groundwater recharge, and increased land subsidence in southern districts. The findings underscore the critical need for urban regeneration to implement the "Sponge City" model and update spatial planning documents according to the basin's revised ecological capacity.

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