Measurement and Prediction of the Potential Occurrence of Floods Under Climate Change Conditions (Case study: Gorgānroud watershed)

Flood management is a comprehensive approach that includes multiple evaluation indicators in the river basin and an effective and stable but complex method. Flood risk assessment provides valuable information for flood management in order to assess vulnerability and exposure to risk. The method of the current research, according to the nature of the problem and the subject under investigation, is descriptive-analytical and applied studies with emphasis on quantitative methods. In the current research, the regional changes in flood occurrences in the Gorgānroud watershed were investigated using information from meteorological stations (synoptic data) over a 30-year period (1999 to 2018), land use, plant cover, topographic moisture index, slope, elevation, lithology, distance from the river, river density, erosion, soil analysis, runoff, and simulated data of mean precipitation obtained from the HadCM3 model in LARS-WG under the SRA1B scenario for the years 2011 to 2045. In this study, two different approaches were employed. In the first approach, the LARS-WG model was used for downscaling to predict the future climate conditions (near and distant future), while in the second approach, the SWAT hydrological model was utilized to assess flood risk. Based on the percentage of potential hazards in the Gorgānroud watershed, zoning was conducted using the SWAT and GIS software in order to delineate the areas at risk. In this study, based on the SWAT model, the daily precipitation and daily temperature of synoptic stations were calibrated. The results have shown that climate change and the alteration of natural environmental conditions in the region have led to various consequences and impacts, including changes in precipitation patterns, the emergence of heterogeneity in historical data series, fluctuations in river water levels, reduction in agricultural production, changes in plant composition and productivity in grasslands, alterations in groundwater levels, and the occurrence of social and economic problems. Some behaviors in the time series of climatic elements are sudden, intense, and unstable, appearing unexpectedly. Physiographies factors such as slope, soil texture, land use, and rock permeability have caused different hydrological responses to precipitation events in various watershed areas, which significantly influence the occurrence and characteristics of flash floods.