جستجوی مقالات مرتبط با کلیدواژه « مدل های cmip6 » در نشریات گروه « زمین شناسی »

Climate change has had irreversible effects on the planet Earth. The impacts of these changes are observable in all natural and human phenomena. One of the affected phenomena by climate change is dust storms. Besides their short-term and long-term effects, these storms significantly influence air quality on both local and global scales. In recent decades, the frequency of dust storms has increased due to climate variations and human activities, and it is predicted that this increasing trend will continue in the future. Investigating the effects of climate change on dust storms in Southwest Asia, as one of the most significant dust storm hotspots globally, holds great importance. The objective of this research is to examine the impacts of climate change and forecast dust storms in Southwest Asia using the GRDL-ESM4 model from the CMIP6 model ensemble under the optimistic scenario (SSP1.2.6) during the near-future period (2021-2060).

Southwest Asia is located in the global desert belt. The intensification of climate change in this region has distinct impacts on the trends of dust storms, especially mineral dust storms. Therefore, this study focuses on forecasting dust storms in Southwest Asia using the CMIP6 model ensemble, specifically the GFDL-ESM4 model, under the optimistic scenario (SSP1-2.6). The research methodology involves initially using a 40-year historical period (1975-2014) to analyze dust storm anomalies. Then, the CMIP6 model ensemble, specifically the GRDL-ESM4 model, is utilized to examine the dust storm trends until the end of the present century. Furthermore, the optimistic scenario (SSP1-2.6) is employed for the near-future forecasting period (2021-2060).

The results show that the maximum amount of dust storms occurs during the summer and spring seasons. In the summer season, the significant increase in temperature and decrease in precipitation contribute to the highest level of dust storms. The spring season exhibits a high level of dust storms compared to other seasons, with northern latitudes having more dust storms than southern latitudes. The minimum dust storm occurrence is observed during the autumn and winter seasons. Autumn is characterized by decreasing temperatures and increasing precipitation processes, leading to a reduction in dust storm frequency. In the winter season, the semi-Arabian Peninsula, especially the eastern regions, experiences the highest dust storm occurrence. In the spring season, the eastern part of the Arabian Peninsula, during the summer season, the southeastern regions of the Arabian Peninsula and southeastern Iran, and during the autumn season, the northern half of Arabia and eastern Iran have the highest frequency of dust storms. According to the optimistic scenario, the summer and spring seasons have the highest dust storm occurrence. Furthermore, it is evident that the intensity of dust storm trends will be higher in the southeastern regions of the Arabian Peninsula, the Makran coasts, the northern half of Iran, northern Arabia, and between the rivers compared to other areas.

In general, southern latitudes experience higher levels of dust storms compared to northern latitudes. The primary center of dust storms is located over the Arabian Peninsula in early winter, gradually shifting towards the eastern regions. During this season, the center of dust storms moves from eastern Arabia to southeastern parts of the Arabian Peninsula and southeastern Iran.

Global warming is a gradual increase in the Earth's temperature generally due to the greenhouse effect caused by increased levels of carbon dioxide. Global warming has had significant consequences for human life, significantly affecting agricultural production, ecosystems, and water resources. The climate system of the Earth responds to a perturbation to the top of the atmosphere radiative balance through a change in temperature. This imbalance constitutes a radiative forcing of the climate system, and the magnitude of the response is determined by the strength of the forcing and the net radiative feedback. Equilibrium Climate Sensitivity (ECS) is an estimate of the eventual steady-state global warming at double CO2 and Transient Climate Response (TCR) is the mean global warming predicted to occur around the time of doubling CO2 in GCM and ESM runs for which atmospheric CO2 concentration is prescribed to increase at 1% per year.   This study aimed to evaluate the performance of Climate Model Intercomparison Project Phase 6 (CMIP6) models by selecting 30 models considering TCR and ECS and to investigate temperature spatial distribution and annual trends in Iran. The performance of these models has been investigated with data from Iran’s fifty-one synoptic stations for the historical period (1980-2014) using the Taylor diagram and box plot. The results showed that most CMIP6 models have good performance in simulating spatial temperature patterns. However, in the area-averaged, 73% of the selected models have estimated the temperature of the country as less than the station data. In general, more than 56% of the models showed a correlation higher than 0.5 compared to station data in the area-averaged temperature of Iran. Four models including CanESM5, INM-CM5-0, TaiESM1, and UKESM1-0-LL have shown the highest performance in estimating the temperature in Iran. The area-averaged annual temperature trend, which was examined by the modified Mann-Kendall test, showed that the temperature trend of CMIP6 models is increasing along with the observational data for all models. Most CMIP6 models, however, have simulated higher warming rates in the historical period, which differs from station data. These differences cannot be explained by internal climate variability (ICV), and the equilibrium climate sensitivity of most CMIP6 models has created a greater rate of warming in the models. For example, models such as CanESM5 and UKESM1-0-LL, which showed the highest trend, had the highest ECS and TCR among all.

Climate change is a major challenge for human society and the natural environment. Evidence suggests that human activities play a role in increasing temperature at various temporal-spatial scales. The effects of climate change can be assessed by analyzing air temperature trends. According to the latest IPCC report, global average temperatures will increase by 1.5 degrees Celsius by the end of this century. The main purpose of this study is to assess CMIP6 projected temperature over different climate zones of Iran and its trend in the future. The result of this study can be useful for a wide range of management areas, especially the study of water resources, snow reserves, agriculture, and tourism.    In this study, the mean annual temperature data of 43 synoptic stations of the Iran Meteorological Organization (IRIMO) were obtained from 1990 to 2009. To evaluate the anomaly and temperature trend in Iran until the end of the 21st century, the data of three models BCC-CSM2-MR, CAMS-CSM1-0, and MRI-ESM2-0 of CMIP6 models under two scenarios of SSP2.4-5 and SSP5.8-5 were used. We divided the period into four twenty-year periods, which are the first period (2020-2040), the second period (2041-2061), the third period (2061-2080), and the fourth period (2081-2100), respectively. To evaluate the air temperature which is the output of selected CMIP6 models, three statistical measures of RMSE, NSE and KGE were used. Using the Delta Change Factor (DCF) method, the bias of the models was corrected. Then, non-parametric Man-Kendall (MK) and Sen’s Slope Estimator tests were used to analyze trend analysis and trend slope in long-term data series.  The maximum temperature is seen on the northern coast of the Persian Gulf and the Sea of Oman and the minimum temperature is seen in the northwest following the heights of the Zagros and also in the north of Iran (Alborz Mountains). The minimum annual temperature of 10.80°C was calculated based on observed data for the period 1990-2009, and the maximum temperature was 27.90°C on the coasts of the Oman Sea in southeastern Iran and Khuzestan province on the shores of the Persian Gulf in southwestern Iran. The intensity of the increase in temperature in Iran in mountainous areas is mainly due to the increase in the minimum temperature rather than to the maximum one.Generally, the intensity of the warming in Iran is mostly projected in cold and temperate regions. There is also a tendency for the temperature to rise further at higher latitudes.  The projected temperature of CMIP6 models based on the SSP2.4-5 and SSP8.5-8 scenarios in Iran over four 20-year periods from 2020 to 2100 showed that the average slope of the temperature trend in Iran will reach 0.05°C per year, which shows an increase by a factor of 0.01 throughout Iran. As a general result, the annual trend of air temperature in Iran, based on observational data and projected output of CMIP6 models, shows warmer climate conditions for Iran. Temperature anomaly was not negative in any of the scenarios and periods; whereas positive anomaly is seen throughout the country. This increase in anomaly can be a major threat to the country's water resources.