The Deterioration of the Quantitative Characteristics of Water in the Lower Part of the Karkheh River Basin, Iran

The Karkheh River Basin, situated in the arid and semi-arid regions of western Iran, faces significant water scarcity challenges.Approximately 87% of the basin's water is allocated for agricultural purposes, with water demand rising from 3.9 km per year in the 1990s to 7.416 km per year in 2021.Over 70% of the rainfall in the basin evaporates, with annual evaporation rates ranging from approximately 2,000 mm in the north to 3,600 mm in the south.During the 2002-2003 hydrological year, total evaporation was recorded at about 16,680 mm.Average annual rainfall across the basin is roughly 450 mm, with significant spatial variation, ranging from 150 mm in the southern areas to 1,000 mm in the northern regions.For the 2002-2003 year, total rainfall was approximately 18,507 mm.Temperature patterns also show notable differences, with average annual temperatures of around 16C in the north and 26C in the south during the same period, reflecting a 62.5% variation.Groundwater resources play a critical role in supplementing the basin's water needs, with total usage reaching approximately 4.0 km annually.Analysis of flow volumes indicates that Q50, representing the median flow, occurs about 50% of the time, while Q5, the least frequent flow, happens roughly once every 20 years.In 2002-2003, the external water contribution to the basin was estimated at just 7.8% of the total rainfall, underscoring the limited availability of water resources in the region.The findings emphasize the growing demand for water across multiple sectors and highlight the urgent need for a comprehensive strategic plan to manage water resources effectively in the Karkheh River Basin.