عنوان مقاله [English]
The climate change and global warming is a widespread problem in the world. Increase in the greenhouse gases is the reason of this climate change (Dettinger et al, 2004, 2). According to IPPC report, average annual temperature of the earth has been raised from 0.3º to 0.6º as a result of spreading the greenhouse gases and this value will increase from 1 to 3.5º by 2100. The main effects of the phenomenon are drought, extreme flood, snowmelting, storms and increasing air temperature in different regions. These phonemes are in the whole world but they are different from each other. Climate change is an important environmental challenge in recent years.
In the north Karun basin, higher than 2500 m in altitude, is covered mainly by snow. Therefore, the snowmelt water supply plays an important role in Karun River. We will analyze the effects of minimum air temperature on snow cover and discharge changes in Karun River. In this basin, snowfall supply of water is more than precipitation rate to whole basin.
According to previous studies in different regions in the world, annual rainfall has downward trend but heavy rains have upward trend. Average air temperature, maximum air temperature, minimum air temperature and evaporation have upper ward trend. In addition, flooding has an increasing trend. However, these parameters have caused decrease in water resources.
The global effects including temperature increase, melting of polarized ice, and global sea level rise are the main results of that the climate changes. Among the negative effects are Non-uniformly distributed rainfall, increase and continuity of the droughts and finally on water resources in all over the world.
Materials and Methods
North Karun watershed is 2300 km2 in area in south west Iran. This is one of the important basins in supplying water resources in southwest Iran. The volume water as resources is almost 10billion m3 in North Karun basin.
The hydrologic data were recorded by power ministry and meteorological organization in 1984-2014. These data are including air minimum temperature, ice daily, snow cover and river discharge.
Results and Discussion
In this research for change assessment, simulation and forecasting the minimum temperature, we have used meteorological data from 4 synoptic stations in the North Karun Basin. We have divided research period in the stations into 2 parts: 30 and 25 years. Therefore, the purpose of this research is to evaluate changes of minimum temperature in the past and to forecast it in the future. We have used CMIP5 for future climate change projections over the HNZ under a very-low forcing scenarios (RCP2.6), a medium stabilization scenarios (RCP4.5) and a very high baseline emission scenarios (RCP8.5). CMIP5 data were interpolated to the spatial scale (0.4˚×0.4˚). We have also made a downscaling by MATLAB software (0.2˚ ×0.2˚). In the following, correction model is used in accordance with the equation:
We have also used indexes Bias, RMSE and R for assessment models to apply them for forecasting data in North Karun basin. The models of CMIP5 under, RCP4.5 and RCP8.5 have been utilized in this study. The output CMIP5 and scenarios RCP4.5 and 8.5 is comparedwith CMIP5 and MNA-44_ICHEC-EC, RCP4.5 scenariochoice for simulation and forecasting.
Eventually temperature changes were evaluated. In addition, we have used to change snow cover of MODIS TERRA and Aqua satellite Image monthly for 2000-2014. An aspect of technical analysis is to predict the future movement of a stock based on past data. Trend analysis is based on the idea that what happened in the past gives an idea of what will happen in the future. A trend can be considered as the general movement over time of a statistically detectable change. The MK test is usually used to assess the trend of a time-series. The purpose of Mann-Kendall (MK) test is to assess if there is a monotonic upward or downward trend of the variables of interest over time. A monotonic upward (downward) trend means that the variable consistently increases (decreases) through time, but the trend may or may not be linear. The MK can be employed instead of a parametric linear regression analysis to test if the slope of the estimated linear regression line is different from zero. The following equation can be used:
The climate change can cause water stress. The increase in air temperature, drought and decrease in water are the signs of climate change in the whole world. The results indicate that there are changes in minimum air temperature, snow cover and discharge in North Karun Basin. The results show that minimum air temperature has upper ward trend at 95% and it is increasing between 0.1Cº to 4.4Cº in particular at cold season (November, December, January, February). In addition, snow cover, ice daily and discharge have decreasing trend. The results of simulator by GCM represent that air temperature trend will perpetuate in this basin at future period. Therefore, the increase in air temperature minimum, decrease in snow cover and discharge can cause water stress in North Karun Basin and Karun River. The results show that increased minimum temperature of air cause decreasing water resources and hydro-electric supply in the feature.