عنوان مقاله [English]
Climate change is one of the effective phenomena on the ecosystems and their resources management. Today, water resources management has special aspects with climate change. Predicting water quality has the same important as water quantity. Increasing global temperature due to climate change has changed the precipitation and river flow-rate pattern in the watersheds. Hence, the quantity and quality of the water resources (especially surface water) is particularly affected by climate variations. Many studies have investigated the climate change impacts on weather parameters; however, changing in water quality factors caused by climate variations has been less studied. Hence, this study has focused on the variations of weather parameters (temperature and precipitation) and forecasting of the surface water quality under different future climate scenarios. For this purpose, the GCM (general circulation model) HadCM3 and LARS-WG down scaling models were used in Eskandari Watershed of Isfahan.
Materials and methods
In this study, the changes of climatic parameters and surface water quality factors in Eskandari Watershed of Isfahan (located in central Iran) were investigated in the base (BP) and future period (FP). The daily minimum (MinT) and maximum (MaxT) temperatures and precipitation data of Daran Station during 1993-2013 (BP) were simulated using HadCM3 general circulation and LARS-WG down scaling models. These parameters then predicted under A1B, A2 and B1 scenarios for the FP (2020-2030). Thereafter, the main quality factors of the surface water including electrical conductivity (EC), acidity (pH) and sodium absorption ratio (SAR) in the FP were estimated by substituting the climatic parameters in the multivariate empirical models derived from water quality and climatic factors in the BP. Then the suitability of water for agriculture and drinking was investigated using Schoeller and Wilcox diagram.
Results and Discussion
Results of the study showed that the MinT and MaxT of the study area will increase under three selected scenarios in the FP except for MaxT which will remain in B1 emission scenario. Precipitation will decrease in all studied scenarios specially in A1B and A2. Surface water quality had a close relationship with the variations of the temperature and precipitation in BP. There will be a greater increase in EC under A2 scenario. There will be the greatest increase of temperature and decrease in precipitation in this scenario as compared to the others which justifies the increase in water salinity. Whereas, pH of the surface water will decrease under three scenarios in the FP. Furthermore, SAR will enhance in all three scenarios which shows water quality degradation in the FP. Changing water type-facies from Ca2+-CO32- in BP to the Mg2+-CO32- in FP under A1B an A2 scenarios also indicates the deterioration of the surface water quality in Eskandari watershed. Although, the water quality of the watershed will degrade, but it will still satisfy the criteria for drinking (based on the Schoeller diagram) and agricultural (based on the Wilcox diagram) uses. It should not be overlooked that the land use type will have more effect on surface water quality rather than the variations of temperature and precipitation in the future. Hence, future anthropogenic activities make it difficult to interpret the effect of predicted climate variations on water resources quality (especially surface water resources). However, monitoring of the factors that affect quality of the water is the essential part of a water resources management plan in a watershed.
Results showed that the MinT in the study area will increase in the FB under three studied scenarios (A1B, A2 and B1); however, MaxT will also increase under A1B and A2 scenarios but it will nearly remain without change under B1 emission scenario. The annual precipitation has also a declining trend in the FP under three emission scenarios which has a negative impact on the surface water quality. Results also showed that EC will increase under three studied scenarios; whereas, pH will decrease with regard to the BP. Besides, SAR will increase as 17% in the FP as compared to the BP. The quality of surface water in the Eskandari watershed will satisfy the required criteria for drinking and irrigation according to the Schoeller and Wilcox classification, respectively, in the FP under three emission scenarios.
Keywords: Climate change, LARS-WG model, Daran Station, Water type and facies.