پژوهشنامه مدیریت حوزه آبخیز (Oct 2024)
The Effect of Climate Change and Future Land Use Using the CA-Markov Model on the Streamflow of the Talar River in Mazandaran Province
Abstract
Extended Abstract Background: In recent years, changes in climate and land use have led to fluctuations in water resources. These changes have affected the river flow, environment, and drinking and agricultural water. Land use change has four important effects on watersheds, namely changes in peak flow characteristics, changes in total runoff volume, changes in water quality, and changes in hydrological balance. To prevent natural disasters, it is important to identify the current conditions and predict the future situation. Overcoming these crises and reducing their adverse effects are only possible in the shadow of management, planning, and relying on practical knowledge. The present study aimed to determine the impact of climate change and land use on the river flow in the Talar basin between 2020 and 2050. Methods: The effects of future land use, climate changes, and their combined effect in the Talar basin (Mazandaran province) have not been seriously investigated using the sixth climate change report. Therefore, this study analyzed data based on CMIP6 climate change scenarios and land use projections for 2035 and 2050. First, the SWAT model was used to evaluate the effects of climate and land use on the river flow in the Talar River basin. After calibration and validation of the model using the best parameters from 2001 to 2020, CMIP6 data were downscaled based on six models and projected under two scenarios SSP2-4.5 and SSP5-8.5. The scale of atmospheric general circulation models was reduced using two methods: the delta method and quantile mapping (Qm). These methods were chosen due to the large scale of the models. In this research, the Markov prediction model (CA-Markov) was used to simulate and predict land use changes for the years 2035 and 2050. Precipitation and temperature data obtained from climate change and land use scenarios were entered into the SWAT model to predict the average monthly flow during the years 2020-2035 and 2020-2050. Results: Calibration and validation at the Kiakola station as the output of the Talar watershed showed that the Nash-Sutcliffe index (NSE) had efficiencies of 0.8 and 0.76, respectively. The best values of the validation indices were obtained by the INM model. The Delta method for downscaled precipitation data and the Qm method for downscaled minimum and maximum temperatures showed better evaluation values. For example, the presented tables show that the values of RMSE, NRMSE, and MAE for the rainfall of the Kiakola station are 2.185, 0.0402, and 1.716, respectively, using the Delta method. All these values show the good accuracy of these downscaling methods for SWAT model inputs to predict the streamflow in the Talar River basin. These methods were implemented for all the studied stations, and the downscaled values of the aforementioned parameters were used to predict the streamflow of the Talar River basin at the Kiakola station. Conclusion: The predicted results for 2035 and 2050 show a decrease in the runoff volume, wetlands, and urban land. Therefore, land use activities in the future should be based on appropriate land use development and land use regulation to reduce the long-term adverse effects of land use changes. In the Talar River basin, land use changes are mainly controlled by internal factors, such as agricultural land expansion and urbanization, while climate change is regarded as an external factor. Both have an important role in changing the hydrological processes of the basin. This study evaluates the combined effects of land use and future climate changes on the water balance in the Talar River basin. The combination of land use change and climate change has a more obvious effect on surface runoff. On a monthly scale, runoff from surface runoff decreases significantly across seasons, indicating that more extreme events (i.e., droughts) could potentially occur in the future. With land use changes, these effects can only be reduced by less than 20%. Therefore, more measures (for example, soil conservation) are needed in addition to land use planning to increase infiltration and aquifer nutrition and, subsequently, reduce risks from land use and climate change impacts. This research presents the effects of changes in land use and climate on the available water in the Talar River basin in the future. Furthermore, this paper presents a study on the use of the SWAT model in hydrology to help the scientific field. The findings of this study can also be useful for officials in reducing water stress through proper management of land use in the future. The results indicate that the average monthly streamflow of the Talar River basin has decreased due to land use changes, such as the expansion of urban areas and the reduction of agricultural land. In the future, changes in land use and land cover (LULC) may affect streamflow. The main drivers of LULC changes include agricultural development, deforestation, urban planning, land tenure policy, and organization development.
