The rainfall-runoff hydrological simulation model based on satellite products with the effect of climate scenarios in the study area of Takab

Abstract

Introduction

Runoff is an important hydrological component in the assessment of water resources. Most water resource applications rely on runoff as an essential hydrologic variable. The hydrology of basins is influenced by many factors, including climate change. Basin discharge estimation is an important step in planning and managing surface water resources, especially in basins that lack reliable flow data. In this study, due to the inappropriate spatial distribution of meteorological stations in the study area of Takab, satellite images and products were used to evaluate the possible effects of climatic factors including rainfall and temperature on runoff. For this purpose, in order to investigate the changes in rainfall and temperature from 1998 to 2020, TRMM and FLDAS satellite products, respectively, were evaluated using different statistical criteria with Takab synoptic station data. The evaluation results indicate the appropriate accuracy of these satellite products compared to the observed values. Choosing a suitable rainfall-runoff model for the catchment area is important for the efficiency of planning and management of water resources. Also, choosing a model requires recognizing the capabilities and limitations of hydrological models of the catchment area, which requires access to meteorological parameters such as rainfall and temperature. According to the studies, the IHACRES hydrological model has been used to estimate the amount of changes in discharge and runoff in many basins. Its purpose is to help water resources engineers describe the relationship between basin runoff and precipitation.



Materials and Methods

Finally, the trend of changes in rainfall and temperature was investigated with the non-parametric Mann-Kendall and Sense's slope tests. Examining the rainfall data of the study area of Takab indicates that the highest amount of rainfall occurs in the 3 months of April, March and November respectively. which is approximately equivalent to 45% of the total annual rainfall of the study area and its values are estimated as 53.1, 40.4 and 39.6 mm per month respectively. Also, the highest and lowest average temperatures of the range are in the months of July and January, respectively, which are estimated at 24.2 and -3.4 degrees Celsius, respectively. In the following, the IHACRES model was used to simulate the river discharge using temperature and rainfall data from satellite products. Also, in this study, the IHACRES model was used to predict production runoff under the influence of climate change and evaluate different climate scenarios. For this purpose this study focused on Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs) scenarios (RCP4.5 and RCP8.5) for the coming years until the year 2100 were used.



Results and Discussion

The flow simulation results from the RCP2.6 scenario indicate that the greatest increase in discharge in the coming period for the Takab study area was estimated for the months of December, November and January. Also, according to the RCP8.5 scenario, the largest flow increase in the future period was calculated in the months of August, July and January, respectively. In addition, the maximum decrease in discharge in both scenarios was simulated in the months of April and May, respectively. According to the obtained results, according to the RCP2.6 and RCP8.5 climate scenarios, the average annual discharge was predicted to be equal to 8.3 and 1.5 cubic meters per second, respectively. In order to evaluate the IHACRES model, the determination coefficient (R2), Nash-Sutcliffe efficiency coefficient (ENS), root mean square error (RMSE) and bias error (Bias) were used in the calibration and validation period. According to the obtained results, these values for the 14-year period of model calibration are 0.82 and 0.80 (-), 1.4 (cubic meters per second) and 0.42, respectively. Also, these values for the validation period were calculated as 0.71 and 0.68 (-), 4.7 (cubic meter per second) and 0.1, respectively.



Conclusions

In this study, to investigate the trend of rainfall and temperature changes from 1998 to 2020, TRMM and FLDAS satellite products, respectively, were evaluated using different statistical criteria with Takab synoptic station data. According to the obtained results, the annual changes of rainfall in the entire study area of Takab are incrementally insignificant. Also, in general, the percentage of annual rainfall changes in the highlands is higher than the average annual rainfall in the plains. After examining the trend of temperature and rainfall data, the IHACRES rainfall-runoff model was used to simulate the discharge. After simulating discharge for the statistical period, different climate scenarios were used to predict production runoff. According to the obtained results, according to the RCP2.6 and RCP8.5 climate scenarios, the average annual discharge was predicted to be equal to 8.3 and 1.5 cubic meters per second, respectively. According to the RCP2.6 scenarios, the predicted discharge has an insignificant upward slope. Also, the percentage of annual changes in river flow according to this scenario was calculated as 19.4%. Also, in the examination of the output of the IHACRES model resulting from the RCP8.5 scenarios, it was observed that the future trend of the river is a significant downward trend. In other words, the percentage of annual changes in the simulated discharge according to this scenario was estimated as -68.1%.