عنوان مقاله [English]
The Earth's climate has been constantly changing throughout the planet history. The industrial revolution and human intervention in the environment in the recent decades made special conditions for rising global temperature. Increase in Earth's temperature has modified the climatic balance by which widespread climate changes have been occurred on the Earth's surface. To study the effects of climate change on different systems in future, the climate variables should be initially simulated. There are various methods for simulating climatic variables; the most prudent of them is the use of the outputs of atmosphere-ocean general circulation models (AO- GCMs). Since these models can simulate climatic variables in large spatial and temporal scales, to use these simulated variables in smaller scales, the output of these models should be scaled down by various techniques. The microscopic statistical method, including the SDSM model, has more advantages, especially when it comes to lower costs and quick assessment of the factors affecting climate change.
Method and methods
The purpose of this study is to predict climate change by the SDSM model using the CanESM2 Climate Change Output based on RCP8.5, RCP4.5, RCP2.6 climate change scenarios for the coming periods of 2040-2011, 2070-2041, and 2100- 2071, as well as to study the annual trend of these changes using the Man-Kendall test and the age-related slope estimator. For this purpose, daily data of rainfall and temperature parameters during the statistical period (1981-2010) were collected from the Meteorological Organization. Using Statistical Downscaling Model (SDSM), these climatic parameters were simulated in a monthly scale and compared with the base period (1981-2010). In the SDSM model three types of data are used for the microscopic metering. Working with this model is briefly summarized as follows: 1) Preparing predictive data and large scale predictors, 2) quality control of data and conversion (for precipitation data), 3) selection of the best predictor variables, 4) calibrating the model, 5) production of weather forecasting using observational predictors, 6) statistical analysis 7) graphical output of model 8) production of climate scenarios using model climate predictors.
Results and discussion
According to the results, it was found that during the 21st century the temperature in the station of Gorgan has increasing trend and precipitation has decreasing trend. In three scenarios RCP8.5, RCP4.5, RCP2.6 there is a decrease in rainfall in the two periods of near future (2040-2011), and the middle (2041-2070) from February to August and in the distant future period (2071-2100) from December to August. The highest precipitation decline occurs in the near future period in June, July and August, with 19.1, 20.9, and 20 mm, and in the middle and the distant future period in May from 28.8 till 47.15 mm. Generally, in all the scenarios, as we move towards the end of the 21st century, the average rainfall will be reduced, and the decrease in the RCP 8.5 scenario is more than the other two scenarios. Given temperature conditions, the general trend of temperature variables in future periods is consistent with the trend of these variables in the base period, with the difference that the temperature will increase slightly in the winter and spring until mid-summer, but from late summer to late fall it will experience a decrease. In the upcoming period, at first the temperatures will be higher in June and in the upcoming mid and in later periods it will be higher in May than that in other months. Moreover, moving from the near future towards the end of the century, the temperature will increase. The augmentation in the RCP 8.5 scenario is more than those of the two other scenarios. However, with the annual precipitation rate, RCP 4.5 and RCP 8.5 scenarios are meaningful and decreasing. In the case of maximum, minimum and mean temperature variations, there is a significant increase. Also, the precipitation drop and temperature rise in the end of the century. The values in the RCP 8.5 scenario are more than those of RCP 2.6 and RCP 4.5 scenarios.
In this research, the simulation of climatic parameters of temperature and precipitation was carried out using several linear models of SDSM and general atmospheric circulation models in Gorgan. The output of the CanESM2 model was simulated under RCP8.5, RCP4.5, RCP2.6 scenarios for subsequent periods in 21 steps. The results showed that temperature data show better correlation with observation data (compared with rainfall data). According to the results, it was found that during the 21st century the temperature and the precipitation would have increasing and decreasing trends, respectively. At Gorgan Station, in the three scenarios RCP8.5, RCP4.5, RCP2.6, in the two near future (2040-2011) and mid-term (2041-2070) from February to August and in the distant future period (2071-2100) between December and August, we observe a decline in rainfall. The highest precipitation values is in the period in June, July and August, at 19.1, 20.9, and 20 mm, and in the middle and long distances in each of the three scenarios it is from May 28.8 to 47.15 mm. In general, in all scenarios the average rainfall will be reduced, as we move towards the end of the 21st century. This decrease in the scenario RCP 8.5 is more than that of the other two scenarios. Regarding temperature variables, the general trend of the variables in future periods is consistent with the trend of these variables in the base period, with the difference that the temperature increased slightly in the winter and spring until mid-summer but with decrease from late summer to late fall. In the upcoming period, the higher temperatures will be more frequent in June and in the upcoming mid and later periods in May than in other months. Also, in the near future towards the end of the century, the temperature will increase higher. This increase the temperatur in the RCP 8.5 scenario is more than those of two other scenarios. It can also be argued that the increase in temperature and precipitation in the spring and summer and the rising rainfall in the autumn seems to be favorable for planning of water resources, and in particular, the planning for the agricultural sector. The trends and drought conditions should be regarded environmental management in order to minimize the potential negative effects of climate change in the study area.