فصلنامه جغرافیای طبیعی
پیاپی 53 (پاییز 1400)

The phenomenon of climate change is one of the vital issues for human beings today. Investigation of air temperature and precipitation in the second rainiest region of the country, namely the western half; It is important. In the present study, observational data of 51 meteorological stations in the region were used as baseline data. For the next period up to 2061 horizon, the output of simulation models in the fifth report of climate change was used in two models of induced upper and middle limits, as microscale data. The non-parametric Man-Kendall test was used to investigate the trend of changes in air temperature and precipitation series. The results showed that in the base period based on observational statistics, in most areas in the series and the pattern of air temperature, there is a significant upward trend. For rainfall, a significant decreasing trend was observed in most areas and a negative slope was observed in all stations. Evaluation of the output of the models in comparison with the base period showed that in the western and Zagros regions of the country, the minimum and maximum air temperatures in the coming decades in the upper and middle limits pattern, respectively, will increase by 3.1 and 1.1 ° C, respectively. Will have. Precipitation in some stations will increase slightly in the spring months, but in the annual pattern in most areas the precipitation will be lower than the base period. Therefore, the rainy region of the western half in the Zagros region of Iran will be accompanied by an increase in air temperature and a decrease in precipitation.

Any changes in the concentrations of greenhouse gases are causing imbalance status in system components. However, these changes along whit their effects the future should be simulated. There are different methods for the use of climate models is the most reliable.Here in this research, climate change status in Dez river basin where a major basin for water and agricultural yields is studied. For this purpose, the PRECIS model was used. PRECIS is an exponential dynamics downscaling model used to estimate the temperature and precipitation rates for the period of 2070 to 2100 under A2 and B2 scenarios. According to the results of climate change assessment under scenario A2 for Dez river basin, precipitation would decrease up to 22% and up to 5 degrees centigrade would rise in average maximum and minimum temperature while concerning B2 scenario, a decrease in precipitation up to 33% and a rise in temperature rise up to 3°C are estimated.

To study the behavior of dry period lengths, precipitation data were used on a daily scale for 45 synoptic stations in Iran (1985-2017). In order to spatially distribute the dry periods, sequences of 10, 20, 30 and more than 30 days were used and turned into zones. The results showed that the highest frequency of long-term dry periods (30 days and more), with 86 events is related to the south-eastern part of Iran and Iranshahr station. The lowest frequency with 3 cases belonged to Rasht station on the southwest coast of the Caspian Sea in northern Iran. The second-order Markov probability distribution was used to evaluate the type of dry period distribution, return continuity and their probability of occurrence. Probability matrix and return period for 10, 20 and 30 day continuities were calculated on a monthly scale and it was determined that June and April were the shortest dry period return periods (18 days) in the arid central and eastern regions of the country with the highest probability of occurrence ( 89%) and the longest return period is related to October and November in the wetlands of the north and northwest coast of the country (338 days) and the lowest probability of occurrence (28%).

Today, climate change is considered a serious challenge to human societies and the environment and has caused anomalies in the Earth's climate system. According to scientists, an increase in the average global temperature is inevitable. In this study, the climatic elements of temperature and precipitation of Ahar synoptic station for the near future (2026-2045), middle future (2046-2065) and distant future (2066-2085) using the outputs of the CanESM2 climate change model. Based on RCP2.6, RCP4.5 and RCP8.5 with SDSM exponential microscale model and also the annual trend of these changes was investigated using Mann-Kendall test. Based on the output of the model, it was determined that in the near future, precipitation will occur in February and November, and in the next two periods, mid and distant, in October, the greatest decrease will occur, and for April, May and August, the precipitation will increase. On average, the minimum temperature will increase to 0.38 degrees Celsius, the average temperature to 0.52 degrees Celsius and the maximum temperature to 0.82 degrees Celsius. Based on the results of Mann-Kendall test, the annual trend of precipitation in the future will be decreasing, the average temperature in the three scenarios will have an increasing and significant trend and the temperature elements (minimum, medium and maximum temperature) in RCP8.5 will be increasing and significant.

Diurnal Temperature Range (DTR) is an important indicator for identifying climate change. The purpose of this study is to analyze the seasonal and annual trends of the Diurnal Temperature Range and their changes during the 20-year statistical period from 2001/03/21 to 2021/03/20 in Fars province. For this purpose, monthly minimum and maximum temperature data, which are the most important parameters related to climate change and affect ecological activities in 26 stations of the province were obtained from the Meteorological Organization. Among the stations in the province, only 13 stations had a statistical length of more than 20 years, which was selected for review and comparison for this study due to the common period, and the desired index was calculated for the selected stations. After performing the thigh homogeneity test on the data, Mann-Kendall statistical and graphical test was used to determine the trend and the sens slop Estimator Nonparametric Method was used to determine the trend slope rate. The highest trend rates and changes in time were observed in summer and the lowest in autumn. In estimating the sens slope to determine the direction of the index trend, it was revealed that some stations have experienced incremental changes of more than 2 degrees Celsius. Maps of trend type and amount of changes were also drawn. Examination of the maps showed that the western half of the province has experienced an increasing trend and the highest rate of change can be seen in the same area.

Karst and karst cavities are one of the most challenging subjects. Given that karst areas cover approximately 20% of the land area, Identifying and investigating the location of karst buried cavities can be useful in various usages such as tourism development, subsidence prevention and karst water resources. In the rifts of Shaho, located in Kermanshah province, karst landforms, including caves and buried cavities, are well stretched. The current study attempted to identify rapid and early karst cavities using an easy and low-cost method in geomorphological studies. To this end, in Shaho rifts (Quri Qaleh cave and its surroundings), two geophysical methods namely Electrical Resistivity Tomography (ERT) and Very Low Frequency Electromagnetism (VLF) were utilized and compared. Initially, by determining the location of the cave on the ground, the profile performing route was designed perpendicular to the cave route. Then, 5 profiles were performed by VLF and 4 profiles by ERT method. Four ERT profiles perpendicular to profiles 2, 4 and 5 of VLF were taken and finally the results of the two methods were compared. In addition to determining the exact location of the cave, the results of both methods revealed anomalies outside the cave. Other findings of the research include the possibility of rapidly achieving the results and the cheaper use of the VLF method compared to other identification methods.

Water resources are one of the most important components of land life and sustainable development. In the present study, the study of time series changes in the area of ​​Jazmourian Playa water areas, using the surface reflection data of Landsat 8 satellite from 2013 to 2019, was considered and the Modified Normalized Water Difference Index (MNDWI) was used to separate the water areas on the images. Then the trend of changes in the area of ​​water areas was estimated. All of these processes and satellite image analysis were performed in the Google Earth Engine software environment, which is a web and open source system for performing spectral and radiometric analyzes on satellite images. ArcGIS 10.5 software was also used to prepare spatial maps. . Findings showed that the area of ​​the seasonal lake of Jazmourian Lake is estimated to be 21426 Km based on MNDWI index, approximately 1515 Km based on automatic water extraction index (AWEI) and 1610 Km2 based on water absorption ratio (WRI) index. On the other hand, the analysis of surface water production of Landsat images showed that the highest rate of change was related to temporary seasonal and new seasonal water zones, so that changes in temporary seasonal zones occupied an area of ​​about 11245 km2 and new seasonal surface zones about 35355 km2. Is. Jazmourian plain water intake is related to the occurrence of seasonal floods and increased rainfall in the basin, so that a high correlation (R2 = 0.89) between the annual rainfall of the basin and the increase in the area of ​​water areas resulting from the MNDWI index has been observed.

Due to climate change and reduction of precipitation as one of its main components, especially in the mountainous areas of the northwest of Iran, it is important to study the important phenomenon of water and snow due to the importance of snow reservoirs in feeding water reserves. Due to the importance of spectral indices in measuring distance and spectral similarity of snow and water phenomena, in the present study, normalized indices of normalized water and snow, as well as normalized indices without snow/ice and water background and Otsu threshold method on the image Landsat 8, has been used as a study area by selecting a part of Sabalan Mountain and the Caspian Sea. The results of the present study showed that, according to the histogram and variance of the bands, the normalized differential indices of water without snow and snow without water, with 100% accuracy and 97% accuracy, respectively, showed high accuracy in extracting and separating water and snow cover phenomena. The results of the implementation of the Otsu binary algorithm also confirmed this and showed the high ability of the desired indicators to extract snow and water phenomena.