عنوان مقاله [English]
Impact of climate change is one of the major human challenges in the third millennium, the main source of which is the increase in greenhouse gases in the Earth's atmosphere. But how much of this gas will enter the Earth's atmosphere by human societies in the future, and consequently what will happen to the Earth's climate system, is not certain. Therefore, a comprehensive and systematic review of climate change in the coming years with the aim of studying regional behaviors and predicting their effects is necessary to provide appropriate and appropriate solutions for decision makers to carry out reliable and coherent planning. Therefore, in order to predict the minimum and maximum temperatures and precipitation of Tajan watersheds in the period 2040-2014, first, the efficiency of 14 different models of general atmospheric circulation under two scenarios of 2.5 RCP and 8.5 RCP in 20 meteorological stations was evaluated and then the statistical downscaling of each model was performed by LARS model.
Data set of AOGCM models is accessible through the Data Distribution Center established by the IPCC in 1998. To access data related to the region in the base and future periods, by entering the spatial coordinates of the desired location as well as the required statistical length in the base period (1985-2005) and Future period (2014-2040) were obtained. The Characterize of these models are given in Table 1. Then, to evaluate the efficiency of the models in simulating the temperature and precipitation of the region, the monthly average of the base period from the output of the models was compared with the observed values and the future period. To create a climate change scenario in each AOGCM model, the values of "difference" for temperature and "ratio" for rainfall between the average year in future periods (2040-2014) and the base period (1985-2005) for each cell were obtained from the computational network. Then climate change scenarios in the future period (compared to the base period, separately for different AOGCM models were created under two emission scenarios RCP2.5 and RCP8.5. In this study, the WG-LARS model was used for Downscaling, which is able to produce a series of meteorological data with statistical characteristics similar to the climatic period, which consists of three main parts: calibration, evaluation and meteorological data.
In this research, out of 14 mentioned models, 6 models EC-EARTH, GISS-E2-R, MIROC-ESM, MIROC-ESM-CHEM, MPI-ESM-MR for temperature and 3 models EC-EARTH, GISS-E2 -R, MIROC-ESM was detected for suitable precipitation. The reason for the rejected models was due to the large changes in the monthly temperature of the future period compared to the base period. In all stations except Sari station, Pesharat and Dasht-e Naz, the minimum and maximum annual temperatures will increase in all models under both scenarios. The highest temperature increase is predicted for MIROC-ESM-CHEM model and the lowest temperature increase is predicted by GISS-E2 and EC-EARTH models. The highest annual minimum temperature increase of AOGCM models under scenario 2 was predicted to be 1.4 ° C and under scenario 8 was predicted to be 1.6 ° C at Burma and Sefidchah stations, respectively. The maximum maximum temperature increase under scenarios 8 and 2 will be in Peshart station (2.2 ° C) and Burma station (1.9 ° C), respectively. It is noteworthy that the temperature pattern changes under scenario 8 will be more intense in all stations (Figure 2).
Also, due to the fact that the meteorological stations were located at different altitudes, the relationship between the rate of temperature changes and altitude difference was investigated, but no significant correlation was found. As the results show, among the meteorological stations under study, the minimum and maximum temperature changes under both scenarios will be more noticeable in Burma and Sefid Chah stations, which may be due to the geographical location of the stations. These two stations are located in the highland lands of watershed, in the easternmost part of Mazandaran province.
The monthly comparison of the average temperature of the AOGCM models and the observational data, in all months, under scenario 2, except September (predicted by the GISS-E2 model) shows the temperature increase. In May, July, then in August and January, the highest temperature increase was observed, and the lowest temperature increase was observed in March, followed by February and September. Also, these comparisons under scenario 8 showed the highest temperature increase in May (2.6 ° C with MIROC-ESM model) and September (2.9 ° C with MIROC-ESM model) and the lowest The increase (0.1 ° C with the EC-EARTH model) will be in March (Figure 3).
The results of seasonal precipitation of AOGCM models under both scenarios show that in spring, autumn and winter there will be a decrease in precipitation and in summer an increase in precipitation. Of course, the amount of change varies under each scenario. The highest percentage of rainfall decrease is 28% under scenario 2 in spring and 65% under scenario 8. On the other hand, the highest increase in rainfall in summer under scenarios 2 and 8 is projected at 50 and 7%, respectively. Also, the average annual rainfall under Scenario 8 in the three models EC-EARTH, GISS-E2 and MIROC-ESM for the next time period shows a decreasing trend. It is noteworthy that the precipitation pattern will also change under the effects of climate change, so that the maximum amount of precipitation has changed from winter and autumn to summer under scenarios 2 and 8 (Figure 4).
With the above analyzes, in general, it can be said that one of the most important changes in the Tajan watersheds is the change in the seasonal rainfall pattern and the increase in temperature in the warm seasons. These natural changes will also affect the river flow regime and peak discharge time, intensification of water cycle, change in precipitation characteristics, change in runoff amount and time, occurrence of drought, major floods and change in evapotranspiration rate. Also, Tajan watersheds as the agricultural center of the country are of great importance in the development of the country. Due to the fact that the reduction of river flow coincides with the period of plant growth and water needs of crops in the basin, it can reduce production in the agricultural sector of the basin. Therefore, the findings of this study affect the macro-planning related to the climate of the region, to estimate changes in surface and groundwater resources of the basin, changes in the performance of agricultural and rangeland products and the status of extreme climatic phenomena such as the number And the severity of flood and drought events and timely awareness will be very effective, as in recent years, due to lack of proper forecasting, or a reduction in the severity of natural disasters, we have witnessed an increase in the aforementioned events in the northern provinces of the country. Also, since the thermal regime plays a decisive role in the distribution of plants, the impact of definite changes in temperature, especially the warming of forest ecosystems, will cause changes in the composition of plant communities and their individual distribution. Usually, with increasing altitude every 100 meters, the temperature decreases by one degree Celsius; In particular, environmentally sensitive areas such as Dudangeh, Chahardangeh and Bola National Park are located in the study area, which shows the importance of natural habitats in the study area. Therefore, this research is the basis for many studies in various fields, including the consequences of climate change on water resources, water efficiency, crop yield, impact on irrigation networks, impact on the distribution of plant species in Hyrcanian forests, etc., which can be Manage and reduce climatic consequences to be useful.