نشریه پژوهشهای تغییرات آب و هوایی
پیاپی 5 (بهار 1400)

One of the disadvantages of earth climate simulator models is the inadequacy of their spatial resolution with downscale studies such as outcome-based evaluations. In many cases, the resulting information should serve politicians as well as local and regional planners to be able to plan and adopt future strategies. For this purpose, downscaling has been proposed. One of the methods that has been used frequently in Iran's climate research is the statistical descent method using SDSM software. With the aim of evaluating the efficiency of this model in different climatic regions of Iran, a representative station with a 41-year statistical period was selected. In order to compare the results of the model with the observed data, criteria such as mean absolute errors, mean squared error, and root mean squared error were used. The results show that the model output for arid and super arid (warm and cold) regions is not very suitable and from the humid regions of the country (northwest and north) to arid and super arid regions (south, southeast, and southwest), it has irrational and inappropriate results. The reason for this is the repetition and lack of rainy day at the stations. In fact, the stations in these areas face overflow or zero number in raining. In the downscaling with the model, uniformity and precipitation rates are two important factors so that uniform distribution of rainfall is very important in increasing the efficiency of the model relative to the amount of precipitation. Therefore, any long-term planning based on the SDSM model predictions in arid and semi-arid regions is associated with extreme errors and uncertainties and will not be reliable and principled.

In this study, the data of (ECMWF) version (ERA5) with spatial resolution of 0.25 * 0.25 degrees and a period of 40 years (1979-1989) of the meridional performance flow function Seasonal changes in the external edge of the Hadley cell in the Northern Hemisphere have been investigated using MATLAB. Findings showed that the outer edge of Hadley cell in winter from 35 to 38 degrees south, in spring from 29 to 32 degrees south, in autumn from 30 to 35.5 degrees South and can be seen in summer from 28 to 29 degrees south; Also, with increasing each year, the outer edge of the Hadley cell in winter, autumn, spring and summer increases by -0.039, -0.048, -0.014 and -0.012 degrees on average. In general, the results show that the expansion of the outer edge of the Hadley cell has increased by 2 to 3.5 degrees latitude in winter and autumn, and shows that it is very prominent compared to the summer and spring seasons. Shows the expansion of the Hadley cell rotation towards higher latitudes.

Changes in temperature and precipitation and, accordingly, climate change along with the occurrence of hazards such as drought and flood have a great impact on the hydrological status of catchments. Therefore, it seems necessary to study the effects of climate change on water resources. In this study, the effect of climate change on the hydrological status of Hablehrood catchment was investigated. Temperature and precipitation changes were studied using minimum temperature, maximum temperature and precipitation data from 1996-2017 and using LARS-WG model, climate change of Hablehrood catchment using HadGEM2-ES model and 2.6 RCP, RCP4.5 and RCP8.5 scenarios were simulated in 2021 to 2050. Then, the hydrological condition of the basin runoff was simulated with the SWAT hydrological model. The results of the LARS model in the baseline period showed a complete agreement of the baseline period with a slight difference with the modeling data. It was also found that in the years 2021 to 2050, the temperature and precipitation have increased in almost all months. The results of the SWAT model also show an appropriate and acceptable correlation between the simulated data and the observed values of Hablehrood basin. In addition, it was found that the increase in rainfall in the catchment has led to an increase in surface runoff in the study area in the forecast period 2021-2050. Finally, the findings of this study showed that the LARS model for investigating the climate change of the basin and the SWAT model have a high capability in simulating the runoff of the basin.

This study aims to provide a perspective of the climate of the eastern provinces of Iran at the end of 21st century to be usd in longterm planning, adoption and mitigation of climate change. This study uses a combined dynamic-statistical approach for downscaling of CanESM global climate model using RegCM4.5 as a dynamic model and change factor as a statistical method over eastern provinces of Iran, including Khorasan Razavi, South and Sistan and Baluchestan. After configuration of the RegCM regional model, the output of the RegCM was statistically downscaled by change factor method over two period of near future (2021-2049) and the distant future (2071-2099) under two IPCC scenarios of RCP4.5 and RCP8.5. The results indicate an annual increase of 4.2oC and 5.5 oC under RCP4.5 and RCP8.5 scenario in near future period (2021-2049) and 8.9oC to 5.5 oC in far future period of 2071-2099, respectively. If in the combined combined dynamical-statistical ownscaling process, the average scenario is considered as the most probalble scenario, then the decrease in precipitation in the east of the country in the near future will be between -11 to -15 percent and in the distant future between -8 to + 149 percent compared to the observation period. Although a small number of scenarios have predicted an increase in precipitation for the region, but due to the relatively large increase in temperature, any effects of increased precipitation will be ineffective due to the prrojected temperature increase in the region and the region will be subject to water stress that requires adaptation sterategy and reducing the consequences of global warming in the region.

Climate systems are complex yet organized systems. Because it is a function of random behavior in different places and years, in this regard, the high-altitude subtropical system by moving to its location in different years, sometimes regular and sometimes random environmental events (drought or wet season, etc.) in one They create the region. These environmental events take place at different levels of equilibrium, thresholds, and hazards. In this paper, in response to this issue, identifying the behavior of high-altitude subtropical systems from equilibrium to hazards, an attempt was made to identify and evaluate this trend in the form of system thinking. Because in the behavior of climatic systems, the interaction of quantitative and qualitative studies is essential. For this purpose, the research method in this study consists of two main parts; In the statistical research method, the received data of pressure level of 500 hPa during the statistical period of 1948-2018 and the monthly precipitation data of 84 synoptic meteorological stations were received and analyzed. In the next step, the statistical results obtained from the high-altitude system were evaluated based on the eight concepts of equilibrium, thresholds or fringes, hazards and environmental disasters in examining the reactions of rural areas in terms of adaptation and reduction of hazards. The results showed that during the period under study, the most effective outer band on Iran as a representative of the expansion of the high northern limit of the subcontinent, has followed several levels of equilibrium, especially static, uniform instantaneous, dynamic and ultra-stable balance and in some years with effect Astaneh or Farin is encountered. These flights can pose a threat to the onset of environmental hazards (severe droughts).

Variations in frequency and intensity of drought have substantial impact on water resources and environment, which in turn are reflected on agriculture, society, and economy. The aim of this study is to investigate the effect of climate change on meteorological drought in Urmia. For this purpose, using rainfall data, the drought of the base period (1986-2005) and the future periods (2031-2050 and 2051-2070) were calculated for 3, 6, 12 and 24-months’ time scales in Urmia. Precipitation for future periods were determined using the CanESM2 Fifth Report Model and three Scenarios (RCP2.6, RCP4.5 and RCP8.5) and were downscaled using the SDSM model. Then the trend values of SPI in baseline and future periods were investigated using Mann-Kendall test. The study of precipitation changes showed that in the first future period, based on two scenarios RCP2.6 and RCP8.5, the average precipitation will increase, but in the second future period there is a very small decrease in precipitation. Also, SPI values on a long-term time scales indicate a higher severity of drought and among the studied scenarios, RCP8.5 shows more severe drought intensity than the base period compared to other scenarios. The results of trend analysis also show significant changes in SPI values in the reference period and future periods based on the RCP8.5 scenario.