Climate and Human Impacts on Semi-Arid River Water Quality

Abstract

Water quality degradation in river ecosystems is a growing global challenge, driven by both anthropogenic activities and climate change. The Kashafroud River in northeastern Iran is a critical water source for nearly two million people, yet it faces mounting pressures from rising temperatures (~1.5 °C over the past three decades), irregular rainfall, frequent droughts and floods, agricultural runoff, industrial effluents, and rapid urbanization. This study analyzes long-term trends in key water quality parameters—electrical conductivity (EC), biological oxygen demand (BOD), and chemical oxygen demand (COD)—over a 13-year period, using statistical modeling and geospatial mapping. Hydroclimatic analysis revealed increasing temperatures and declining precipitation across the basin, providing important context for understanding vegetation degradation, expansion of bare land, and water quality deterioration. The results show BOD levels increased by 20% and COD by 15%, strongly correlating with climate variability and intensifying pollution sources. Inline with other research, we concluded that, the Kashafroud River is heavily impacted by urban wastewater, with pollution loads far exceeding its natural assimilation capacity. Hydrological and water quality monitoring is essential for managing pollution and protecting downstream water users. These findings highlight the urgent need for integrated water management strategies that combine stricter industrial discharge standards, improved control of agricultural runoff, and climate-resilient urban planning. By demonstrating how climatic and human pressures jointly degrade water quality, the study offers practical insights for conservation of the Kashafroud River and contributes to global understanding of freshwater management in arid and semi-arid regions.