The evaluation of climate change and its side effects on the hydrological processes of the basin can increasingly help in dealing with the challenges that water resource managers and planners face in future courses. These side effects are investigated using the simulation of hydrological processes with the help of physical rainfall‐runoff model. Hydrological models provide a framework for examining the relationship between climate and water resources. This research aims at the investigation of the effect of climate change on the runoff of Gharesou, which is one of the main branches of the “Karkheh” River in Iran during the periods 2040–2069. To achieve this, the distributed hydrological model Soil and Water Assessment Tool (SWAT) – a model that is sensitive to the changes in land, water, and climate – has been used with the aim of evaluating the impact of climate change on the hydrology of the Gharesou Basin. For this reason, first, the continuous distributed model of rainfall‐runoff SWAT for the period 1971–2000 has been calibrated and validated. Next, with the aim of evaluating the impact of climate change and global warming on the basin hydrology for the period 2040–2069, HadCM3‐AR4 global climate model data under the A2 scenario – from the SRES scenario set‐haves been downscaled. Eventually, the downscaled climate data haves been introduced in the SWAT model, and the future runoff changes have been studied. The results showed that the temperature increases in most of the months, and the precipitation rate exhibits a change in the range of ±30%. Moreover, the produced runoff in this period changes from −90 to 120% during different months.
The joint behaviour of flood variables under climate change is of high importance for the economics of projects and risk reduction. This study investigates the implications of climate change using Gumbel-Hougaard copula function for future bivariate of flood peak and volume variables, in Azarshahr chay watershed. Canadian Earth system model (CanESM2) under three Representative Concentration Pathways (RCPs) along with statistical downscaling method (SDSM) and soil and water assessment tool (SWAT) were adopted to assess both baseline (1976-2005) and future (2030-2059) periods. Bivariate analysis of Copula improved the accuracy of model with an average NSE of 0.97 for all scenarios. Joint return period for severe floods has declined in the future, especially in RCP8.5. For a constant discharge and volume, joint return periods at the base period, RCP2.6, RCP4.5 and RCP8.5 were 24, 10, 13 and 9 years, respectively. Multivariate analysis may also provide useful information for flood risk assessment.
Due to the fact that one of the important ways of describing the performance of basins is to use the hydrological signatures, the present study is to investigate the effects of climate change using the hydrological signatures in Azarshahr Chay basin, Iran. To this end, Canadian Earth system model (CanESM2) is first used to predict future climate change (2030–2059) under two Representative Concentration Pathways (RCP2.6 and RCP8.5). Six signature indices were extracted from flow duration curve (FDC) as follows: runoff ratio (RR), high-segment volume (FHV), low-segment volume (FLV), mid-segment slope (FMS), mid-range flow (FMM), and maximum peak discharge (DiffMaxPeak). These signature indices act as sorts of fingerprints representing differences in the hydrological behavior of the basin. The results indicate that the most significant changes in the future hydrological response are related to the FHV and FLV and FMS indices. The BiasFHV index indicates an increase in high discharge rates under RCP8.5 scenario, compared to the baseline period and the RCP2.6 scenario, as well. The mean annual discharge rate, however, is lower than the discharge rate under this scenario. Generally, for the RCP8.5 scenario, the changes in the signature indices in both high discharges and low discharges are significant.
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