Monitoring and prediction effect of climate change on alteration of water catchment balance on Golestan Dam 2

Introduction Natural and anthropogenic pressures on hydrological systems often coexist and mutually interact, contributing to deeply modify watershed hydrology and determining relevant alterations in many hydrological processes, which are commonly referred to as “hydrological changes. Natural pressures are essentially related to modifications induced by the intrinsic variability of the different natural processes involved in the water cycle. Anthropogenic pressures are related to all the human activities (e.g., pollution of streams and aquifers, agricultural and irrigation practices, overexploitation of water resources, runoff regimentation and regulation, etc.) and human-induced alterations on climate forcings (e.g., greenhouse gases emission in atmosphere, heat island effect, etc.) and basins’ characteristics (e.g., morphology, land cover and use, soil imperviousness degree, etc.) that may have a role in modifying the catchment scale hydrological dynamics(Pumo, et al.,2017). Iran is located in a dry and semi-arid region facing the water crisis. Therefore, predictions and monitoring the water balance in different water basins can be an important step in land-use planning and access to the sustainable development. Therefore, present study has investigated the surplus and scarcity of available water in drainage basin of Golestan II Dam based on Thornthwaite water balance model for two base (1971- 2011) and future (2012- 2048) period by using the results of two climate change scenarios of RCP8.5 and RCP4.5.
Materials and Methods In this research, for evaluation of predictions and monitoring of water balance changes in drainage basin of Golestan II Dam, Thornthwaite water balance model has been used based on two different time series. In this research, base data has 40-year time series from 1971 to 2011 and the other one is simulated data from 2012 to 2048. Climate data which is used in this research is Thornthwaite water balance model consist of temperature and precipitation.
Therefore, for base period, data is monthly available and for the simulated data of future temperature and precipitation, it is extracted from data output of prediction components of GISS large scale model from BCSD database (NASA affiliate) with resolution of 2.5 * 2.5. It has to be mentioned that predictions has been done by using two climate change scenarios of RCP8.5 and RCP4.5. Since the resolution of the GISS model is large in scale, so by using a multivariate regression method, output of temperature and precipitation in dimensions of 4000*4000 meters for 137 study pixels changed to Tiny Scale by using Matlab software. Also for locating and mapping of spatial-temporal distribution of water balance, the Arc GIS software and the Kriging interpolation method have been used.
Findings: The results of this research indicate that the average temperature of the basin is 12.51 ° C, which respectively will increase to 16.60, and 16.96 ° C, according to RCP4.5 and RCP8.5 scenarios.
The outputs for the variation of the precipitation component show the decreasing trend for both base and simulated study periods. The interesting point is that for base period slope of precipitation is -41 mm per decade, but for RCP4.5 and RCP8.5 and will be -9 and -18 mm per decade respectively. Finally, the outputs of the present research show that, based on the long-term average of the base period, the average of water scarcity was -505 mm and the surplus was 61 mm, while considering the global warming based on the RCP4.5 scenarios, the average annual water scarcity is -694 mm and surplus of 2 mm. But regarding the results analysis of RCP8.5, the average annual scarcity and surplus in the basin are respectively -715 and 1 mm.
Therefore, due to future climate change, the Golestan Dam drainage basin is expected to suffer from severe water scarcity. So the Risk management should be guided in allocation of water resources for various activities of the society that prevent water challenge to become water crisis and enable us for adapting to the future water conflicts and decreasing the negative effects by adopting various policies.