Nowadays, climate change is one of the most important crises that affect the environment. Climate change can alter the rain pattern and cause floods which have emerged as significant challenges to global water resources management and water security. In this paper, Krun River (one of Iran’s rivers) is studied which goes through Ahvaz city. The flooding of this river is simulated with Hec-Ras and GIS software. At first, the effects of climate change on the maximum sea level of the river were studied, and then the consequences of the flood on agricultural lands, and urban and rural areas were evaluated. Maximum depths occurred upstream and downstream of Ahvaz city, which contains agricultural lands on the right and buildings on the left side. In conclusion, some water management strategies for reducing the flood impacts on Karun River are listed. This paper is a useful guidance for civil engineers and policymakers in water and climate management.