Ziba Kounani; Alireza Ildoromi; hossien zenivand; Hamid Nouri
Abstract
1-Introduction Due to the importance of climate change and the effects it can have on runoff, developing a suitable model for simulating the present and future conditions of the catchment areas is of great importance (Rajabi et al, 2012). Nowadays, the LARS-WG and SDSM models are used to downscale environmental ...
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1-Introduction Due to the importance of climate change and the effects it can have on runoff, developing a suitable model for simulating the present and future conditions of the catchment areas is of great importance (Rajabi et al, 2012). Nowadays, the LARS-WG and SDSM models are used to downscale environmental parameters in climate change studies nowadays. Studies show that the SDSM model has less uncertainty and a more complex simulation process, and the LARS-WG model with simpler process and faster performance is more efficient (Aghashahi et al., 2012). Considering that many of Iran's watersheds lack hydrometric stations, it is of great importance to use those methods that can estimate the amount of runoff obtained from the rainfall. Therefore, the present study aimed to investigate the role of climate change in estimating runoff from the Silakhor-Rahimabad basin of Lorestan using a rainfall-runoff model (SIMHYD). 2-Methodology Silakhor-Rahimabad basin is in the catchment area of Dez Dam in Borujerd, Lorestan Province, which is located between N 33º 45¢ and 34º 7¢ and E 48º 29¢ and 48º 57¢. First, the baseline data including observation data of minimum temperature, maximum temperature, precipitation and sunshine during the period 1990-2014, and rainfall-runoff data including evaporation, rainfall and flow data, which were available, were received from the General Department of Aerology and Regional Water Authority of Lorestan Province, respectively. In this study, the daily data from Borujerd metrological synoptic station were used as the basis because they were complete and the elevation of the station was equal to the average of other stations’ elevations. For the evapotranspiration variable, the mean daily data from Rahimabad, Borujerd, and Silakhor stations were used, the mean daily data from the six rain-sensing stations for the rainfall variable. Moreover, Rahimabad hydrometric station at the outlet was used as the base station to observe the runoff variation in the basin. 3-Results and Discussion The results of the evaluation of criteria show that the LARS-WG model has a good ability to simulate rainfall parameters, minimum temperature, and maximum station. The simulated precipitation is in good agreement with the observed values (Table 1 and 2). After assuring the ability of the LARS-WG model to produce the rainfall data, minimum and maximum temperatures of Silakhor-Rahimabad Basin, the output of the HADCM3 model was downscaled under the scenarios A2 and B1, the parameters were predicted and compared with their values in the period 1990-2014 (Figures 2, 3 and 4). The results of the LARS-WG model indicate a decreasing trend of precipitation and temperature rise under both scenarios A2 and B1 for the period 2046-2065. The average amounts of annual rainfall predicted under the scenarios A2 and B1 are 451.445 and 4.420 mm, respectively. If the annual rainfall is 453.8 mm in the base period, the study area will observe a decrease in precipitation from 51.0 to 20.7 percent. The results obtained in the SDSM model under the two climate scenarios A2 and B2 for the future period indicate that the average air temperature is increasing and in the period 2050, the monthly average temperature, compared to the 1990-2014 period, increases in most months of the year. Also, rainfall has a decreasing trend in this period (Figure 5). Investigations show that the model efficiency has a direct correlation with the recharge coefficient, infiltration coefficient and soil moisture storage capacity. The effects of climate change on runoff are presented in Figures 9-16. In the period 2046-2065, the amount of runoff in the studied basin will decrease compared to the 1990-2014 period. This decrease in runoff rate can be attributed to the increase in temperature, followed by an increase in evaporation and a decrease in rainfall. Regarding the study of temperature and rainfall for the future period and monthly runoff, it is observed that the amount of runoff will decrease in the future period. 4-Conclusion In recent decades, the increase in greenhouse gases and thereby, the rise in temperature, have made Earth’s climate system imbalanced and caused massive climate change in most parts of the planet. Therefore, it seems necessary to apply climate predictions in national macro plans, especially in relation to natural disasters. The results indicate the decrease in precipitation and temperature rise in both SDSM and LARS-WG models. Also, in the present study, the SDSM model showed more variations than the LARS-WG model. Finally, the results obtained in both statistical downscaling models indicate the decreased amount of runoff in the studied basin is in the future period. In the study of the effect of climate change on runoff in the studied area, according to the values of Nash-Sutcliff coefficient and the coefficient of determination obtained at the calibration step (0.63 and 0.779, respectively) and the verification step (0.61 and 0.61, respectively), it is observed that the SIMHYD model has acceptable performance in the studied basin. These results are consistent with the findings of Aghashahi et al. (2012), Rajabi et al. (2013), Zolgharnein et al. (2013), Zhang et al. (2014).
Hamed Gholamian; Alireza Ildoromi
Abstract
1-IntroductionIn the catchment areas without statistics or incomplete statistics, the extraction of flood characteristics and the provision of water resources and sediment transport analysis are appropriate using empirical methods or models based on the watershed characteristics. One of these methods ...
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1-IntroductionIn the catchment areas without statistics or incomplete statistics, the extraction of flood characteristics and the provision of water resources and sediment transport analysis are appropriate using empirical methods or models based on the watershed characteristics. One of these methods is the use of the capabilities and capabilities of hydrological models in simulating the hydrological processes (Valderz et al., 1979). Rainfall-runoff models, most notably the GIUH hydrograph model and the WinTR-55 hydrologic model, are suitable tools for the study and estimation of maximum hydrograph discharge using geomorphologic parameters of the region (Ghorbani et al., 2015). The purpose of this study was to estimate maximum flood discharge, transfer capacity, and sediment yield of the Kermanshah River using the GIUH and WinTR-55 models. 2-MethodologySanqor basin, with an area of 6317 hectares and minimum and maximum heights of 1500 and 3300 m, respectively, is located in the northeast of Kermanshah province and part of Karkheh watershed. Average values of annual rainfall and temperature are 586.9 mm and 12.9 °C. The WinTR-55 model uses parameters, such as main channel length (flow length), channel gradient (flow gradient), manning roughness coefficient, width of waterway floor, and the slope of margins to determine the effects of flow type and velocity on the discharge peak output and water and sediment transport capacity in the basin. To this end, the area was divided into eight hydrological sub-basins after registration of the basin situation. After estimating the geomorphologic and hydraulic parameters of the canal, the discharge was estimated with different return periods using the WinTR-55 and GIUH models. Geomorphologic proportions include length ratio, branching ratio, area ratio, drainage network, and ranking of riverbeds in the basin (Valderz et al., 1979).3-Results and DiscussionThe estimation results of velocity types in each sub-basin with the WinTR-55 model indicate that the laminar flow in the flood basin were on the surface and not inside the channel, but flow frequency was low with high water content. However, centralized and channelized flows were flooded and concentrated, flowing through the canal or small or large drains. Peak discharge values estimated by the GIUH model were, on average, 6.52% higher than those estimated by the WinTR-55 model. The S3 and S4 sub-basins with low gradients and high roughness coefficients had low flow velocities. In S2, S6, and S8 sub-basins, on the other hand, the discharge and flow rate increased due to a high slope. Estimated peak discharge values by the GIUH model showed increases in all sub-basins other than S1 sub-basin and in the outlet relative to the peaks calculated using the WinTR-55 model. Discharge changes obtained from the GIUH increased on average by 76.1% and 7.1% in the outlet and in the S1 sub-basin, respectively, compared to that calculated by the WinTR-55 model. In the S2, S3, S4, S5, S6, S7, and S8 sub-basins, average increases were 7.31, 5.13, 5.98, 6.3, 6.9, 5.8, and 6.67 percent, respectively. The model calibration d and the sensitivity analysis of the flow parameter were done using the canal slope and the results were investigated at the basin output. The results of the model for a change in the slope of the waterway showed a low effect of the slope on the outlet flow variations. The evaluation results of GIUH and WinTR-55 models in peak discharge estimation with observational data by correlation coefficient (R) and root mean square error (RMSE) indicate good efficiency of both models. R values of 0.90 and 0.97 were obtained between observational and calculated data by the GIUH model by the WinTR-55 model, respectively. The RMSE values were very insignificant in the estimation of observed discharge and those estimated by the WinTR-55 model and the geomorphologic hydrograph unit method.4- ConclusionIn this study, the efficiency of WinTR-55 and GIUH models was investigated in peak discharge estimation. The results showed that there was a high flow rate in S1, S2, S6, and S8 sub-basins due to the high mountainous nature, along increased erosion and sediment transport capacity. In S3, S4, S5, and S7 sub-basins, transfer capacity and sedimentation dropped due to low slope and slower flow rate. The estimated discharge values of S8 and S6 sub-basins by the GIUH method increased by 8.31 and 6.67 percent, respectively, compared to those estimated by the WinTR-55 model, which is due to the increased gradient and its role in discharges calculated by both models. The discharge rate in the area outlet estimated by the GIUH method increased by 1.76% compared to that obtained by the WinTR-55 model, indicating the effect of geomorphologic parameters on the calculation of peak discharge in the basin. Assessments of R2 and RMSE showed that the efficiency of the WinTR-55 model was high at maximum average discharge rate for all return periods, with average RMSE values of 0.66 and 0.32 for the GIUH and WinTR-55 models, respectively. The results showed a high correlation between observational and calculated data obtained from both models. Additionally, the calculated RMSE values showed that the GIUH and WinTR-55 models had high and acceptable performance in peak discharge estimation and could well analyze the erosion and sedimentation conditions.Keywords: Hydrograph, Erosion and Deposition, Flow Velocity, Manning Roughness Coefficient, Sonqor Watershed5-References Ghorbani, M., Asadi, A., Jabari, H., & Farsadizadeh, D. (2015). Extraction of Instantaneous Unit Graph Hydrocopy (IUH) Using Shannon Entropy Theory, Journal of Watershed Management, 5(10).Valders, J.B., Fialloand, Y., & Rodriguez-Iturbe, I. (1979). A rainfall–runoff analysis of the geomorphologic IUH. Water Resources, Res, 15(6), 1421–1434.
