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.

This study aims to investigate the possibility of hydrological simulation of the Azna-Aligoudarz area, which is located in the upper reaches of Karoun Bozorg basin and in the east of Lorestan province. To carry out this research, the daily meteorological data related to the Aligoudarz synoptic station and the rainfall of Kamandan and Dareh Takht rain gauge stations in the period of 1991-2023, the observational discharge related to the Marbareh hydrometric station in the period of 1991-2021, soil map, land use and digital elevation map of Azna-Aligoudarz basin was used. The period of 1991 and 1992 was considered for warm up the model, the validation period from 1993 to 2016, and the validation period from 2017 to 2021. Based on the simulation done in this area, the model had weakness in simulation. After the initial simulation, the model was calibrated. After analyzing the sensitivity of different parameters, 22 effective parameters were selected and the model was calibrated. The evaluation results showed that the NSE value of 0.60 and 0.56 and the R2 coefficient value of 0.61 and 0.78 respectively were obtained for the calibration and validation stages. Based on the coefficients obtained in both calibration and validation stages, it was found that the model had a satisfactory accuracy in the hydrological simulation of Azna-Aligoudarz area.

This paper deals with parameter estimation of SWAT model by means of streamflow data assimilation and application of calibrated model for hydrological simulation of Mahabad River leading to Urmia Lake. Data assimilation algorithem is compared with SUFI2 algorithem. SUFI2 is an uncertaintybased optimization method first developed for auto-calibration of environmental and water resource models. Due to availablity in SWAT-CUP package this is usually used for calibration of SWAT. To illustrate capabilities of data assimilation for calibration of the model and prediction of the river discharge, Ensemble Kalman Filter (EnKF) is utilized in a joint state-parameter estimation framework. Both coding EnKF and calling SWAT is done in MATLAB environment. Results showed that the joint state-parameter estimation using EnKF for SWAT, lead to improvement of accuracy of simulation and prediction of Mahabad River’s monthly discharge at Bitass hydrometery gauge compared to parameter estimation of the model using SUFI2.

Urmia Lake, located in north-west of Iran, has been exposed to various threats such as drought, construction of dams, land use changes and increased global temperature. Due to the importance of Urmia Lake, it is feasible to conduct different kinds of studies to identify the problems of its watershed. The main objective of this study was to evaluate SWAT program’s ability to simulate runoff in Urmia Lake watershed with an area of 52000 km2. The model was run for the 1980-1997 period. Calibration and validation periods were from 1980 to 1991 and from 1992 to 1997, respectively. The results of calibration for 10% and 85% of hydrometric stations were very good and suitable, respectively. Also, validation results for 25% and 45% of hydrometric stations were very good and suitable, respectively. These results show the high ability of SWAT model to simulate discharges in Urmia Lake watershed. Moreover, some factors influencing inflow to the lake in recent years were evaluated. The outcomes revealed that recent changes (dam cconstructions, climate change and land use change) in the watershed have caused inflow volume to the lake to decrease by 80%. So, if natural management conditions had prevailed in the watershed, the Lake’s conditions would have been much better.

Flood is one of the most important threats to human society, which has increased in recent decades with the increase in population and climate change. Therefore, studying the features of the basins that are related to the level of flooding can help to properly manage this risk. Nowadays, several methods such as morphological characteristics, This research was carried out using SWAT hydrological model in 21 sub-basins of Sarbaz watershed located in Sistan and Baluchistan province. After preparing the parameters and input data, while considering two years for warming, the model was recalibrated for a 17-year period from 1999 to 2016 and then validated during a five-year period from 2017 to 2021. The results obtained in the calibration stage were NS=0. 76 and R2=0. 86 and in the validation stage NS=0. 56 and R2=0. 58. The initial curve number parameter for medium humidity conditions and the alpha parameter in the return flow had the greatest effect in the sensitivity analysis. The results showed that sub-basin 20 with an average runoff height of 2. 46 was ranked first and sub-basin 10 with a runoff height of 0. 06 was ranked last. Based on the explanation and Nash-Sutcliffe, it can be concluded that the model has performed well in the simulation of Sarbaz watershed and can be used for modeling in the basin. Flood control by prioritizing flooding in sub-basins and by implementing management measures to improve pasture coverage and build watershed structures in the Sarbaz river basin has reduced the amount of flood discharge and prevented sudden damages.

Life in Esfahan province is dependent on Zayandeh Rud. Therefore, sustaining the quality and quantity of Zayandeh Rud water is of much importance. The first step for adopting correct management decisions is to have continuous awareness of water quality and quantity, temporal changes, and spatial variations and, eventually, specification of main source of pollution. One of the models being used worldwide in such studies is SWAT. The first step in using this king of models is to prove their ability to simulate hydrologic cycle in a the watershed. The main goal of this study was to assess SWAT performance in Zayandeh Rud watershed in order to simulate river flow rate values. Model Calibration and validation were done using average daily flow in four stations named Ghal’e Shahrokh, Zayandeh Rud Dam, Pole Kole and Varzaneh. Observed and simulated values were compared by statistics including R2, NS and COE values to evaluate the model predictions against the observed values. The results of these values for flows at four stations for calibration process ranged between 60.2 to 80.1, 59.4 to 79.0 and 72.6 to 82.0, respectively. According to previous studies and the quality of the data used in this study, these values seem acceptable. The values for validation period were 60.4 to 70.2, 60.1 to 69.1 and 64.7 to 70.8, respectively. Among these four stations, measured and simulated flows at Pole Kole and Ghal’e Shahrokh matched well and weak, respectively. In general, the results showed that SWAT could be a proper tool for simulating the flow rate values of the river.

SWAT hydrological models are one of the methods of estimating runoff obtained from rainfall at points without hydrometric stations. In other words, by simulating the process of converting precipitation into runoff, these models are able to estimate the amount of runoff in watersheds without measuring stations with the least possible time and cost.Based on this, the current study has been conducted with the aim of evaluating the power of the SWAT hydrological model in climatic conditions and simulating the outflow of rivers in the Tajen watershed and comparing it with observations. The most important data used in the research include vegetation, altitude classes, slope, climate data (wind, rain, maximum temperature, minimum temperature), climate changes and climate change conditions, etc.The results of this study show that the error rate of the LARS-WG hydrological model in climate conditions and in the simulation of runoff and average daily discharge was very low, so that the Nash-Sutcliffe coefficient of the simulated daily discharge compared to the observed discharge in the period from 1998 to 2014, during calibration, was more than 0.50, which after re-optimization Soil parameters, this coefficient was obtained in the validation stage (2018-2014) above 0.74 for daily discharge. And this is an indication of the low level of model error in simulating the outflow of the watershed.Keywords: SWAT hydrological model, climatic conditions, Tajen watershed.

One of the main concerns in recent years with regard to climate change and global warming is how to efficiently manage the water resources of the world. Insufficient or unavailable hydro climatological data further aggravate the difficulty of good water management.Hence the use of hydrologic and hydraulic models is a possible solution to ease the job of the water managers. In this research, Soil and Water Assessment Tools (SWAT) are used to predict and validate the discharge in Taleghan Watershed of Iran. The inputs required include soil, land use and DEM layers with hydro climatological data.Statistical methods were used for calibration and validation of the SWAT model. The results indicate that the observed and predicted discharge have the least mean absolute relative error both in the annual and monthly periods. From the SPSS analysis, these values were found to be not significant at 95% probability for the annual and monthly discharges for the calibration and validation periods. The study illustrates the usefulness of the SWAT Model in predicting runoff components in a watershed. The annual results in Taleghan catchments during 1987 and 2007 indicate an increasing 7.3% surface runoff and decreasing 11.3% and 11% interflow and groundwater flow respectively.

Study of water balance is absolutely important for investigation of the hydrology cycle, and preparation of water balance components in the watersheds requires many spatial data and their analyzing; so new technologies, models and tools such as GIS are needed. In this study, the SWAT model, which is a conceptual and semi-distributed model in the water and sediment balance simulation, was used in Aharchay watershed, Ahar, East Azarbayjan Province. Efficiency of the model in hydrologic simulation for this area is evaluated. Meteorology and hydrometers data of 1979-2010 was selected for this simulation; the average amount of rainfall and evapotranspiration were obtained 559. 8 and 299. 1 mm respectively. The period of 1982-2002 were used for calibration and 2003-2010 for validation. Calibration and validation processes were performed using SWAT-CUP software and PSO algorithm. Nash-Sutcliffe efficiency coefficients for water simulation were 0. 39 for calibration and-6. 7 for validation. Results showed that water balance simulation was not performed perfectly. Deficiency of required information and use of different data periods in calibration and validation were some of the effective factors which reduced the efficiency coefficients of the model.

Introduction: SWAT is a continuous-time model that operates on a daily time step at the basin scale. The objective of such a model is to predict the long-term impacts of management and the timing of agricultural practices within a year (i. e., crop rotations, planting and harvest dates, irrigation, fertilizer, and pesticide application rates and timing) on large basins. It could, at the basin scale, be used to simulate the water and nutrients cycle of landscapes whose dominant land use is agriculture. It could also help assess the environmental efficiency of best management practices and alternative management policies. The SWAT model uses a twolevel disaggregation scheme: a preliminary sub-basin identification is carried out based on topographic criteria followed by further discretization, using land use and soil type considerations. Areas with the same soil type and land use form a Hydrologic Response Unit (HRU), a basic computational unit assumed to be homogeneous in hydrologic response to land cover changes. The development of the digital computer has added a new dimension to hydrology. Previously, finding solutions for different problems took hours with a pen and pencil method, but now it takes seconds with modern computers. Moreover, much more complex methods of analysis are now feasible because of the speed of the solution-finding provided by the computer. The impact of the computer has been particularly great in the area of rainfall-runoff modeling. As flood routing and unit hydrograph analysis are mathematical modeling’ s, surfacewater hydrology is, historically, concerned with modeling. Due to the climate type and the spatial and temporal inconsistency of rainfall in Iran, large floods cause many damages in different parts of the country annually, as the Mediterranean climate and different weather conditions throughout a year provide the ground for the majority of short-term atmospheric rainfall. Materials and methods: Karkheh Basin is one of the main watersheds of Iran which has a Mediterranean climate whose level increases during the spring due to simultaneous rains and snowmelt. As one of the most important hydrological processes of the watershed for better understanding the hydrological issues of flood control structures for long-term planning, applying best management practices and making better use of their potentials, Runoff simulation plays an important role in water resources studies. Thus, to calibrate the model, select sensitive parameters were used in the sensitivity analysis step. Having imported the sensitive parameters into SWAT-CUP software, they were repeated 500 times with the SUFI2 algorithm, and finally, the optimal value for each parameter was determined. Result: At Hamidiyeh station, the Nash Sutcliffe coefficient was-0. 19 and-0. 04 in both calibration and validation periods, respectively, and was 0. 76 and 0. 77 in Chamangir Station, respectively. The coefficients of determination for the Hamidiyeh station in the calibration and validation periods were 0. 02 and 0. 22, respectively, and for the Chamangir station, they were 0. 88 and 0. 75, respectively. . This study investigated simulated runoff, using the SWAT model based on the meteorological data regarding the Karkheh watershed. A comparison of simulated runoff results with observational runoff at the hydrometric stations was performed automatically by the SWAT_CUP software package SUFI2 algorithm. Correlation between observed and simulated data was calculated based on the Nash Sutcliffe coefficient and the determination coefficient at different stations of the basin. Nash coefficient-Sutcliffe and coefficient of determination at all hydrometric stations except for the five stations which differed in their calibration and validation periods, were found to be close to their optimum values. Discussion and Conclusion: The coefficient-Sutcliffe of the other 6 stations was more than 0. 5, indicating that the model was capable of simulating runoff. In the mirage stations of Sarab Seyed Ali, Pulchehr, and Noorabad, the SWAT model failed to simulate runoff well, which could be due to the location of these stations in the elevated areas of the basin and its branches that were snowy. The lack of proper distribution of meteorological stations in these areas makes the model unable to simulate well the snow runoff. In Hamidiyeh and Pai-Paul stations, the SWAT model was could not establish a reliable relationship between the observed and simulated runoff due to the impact of the construction of the Shahid Abbaspour Dam on the river flow hydraulics.