فصلنامه مطالعات جغرافیایی مناطق خشک
پیاپی 35 (بهار 1398)

The 10-year drought event from 2007 to 2017 caused a completely different behavior of groundwater of the Ilam-Sarvak karstic aquifers in northern Khuzestan in two regions Izeh (with a drop of about 120 meters) and Lali (with a drop of about 20 meters). In this paper, the drawdown in the Izeh karstic aquifers and the reduction of discharge of karstic wells are compared to the Lali aquifer based on their hydrogeological behavior. Groundwater data were collected and corrected in five calcareous wells. The hydrographs of the depth of the water wells have been prepared and the average annual and total drawdown in the two regions have been compared. In order to identify the reason for the significant difference in drawdown of groundwater level in the studied aquifers, the lineaments were extracted using ArcGIS satellite images using Bing satellite imagery. The average drawdown of Shavish and Tanush karstic aquifers in Izeh is 129.1 meters, and in the Gurpi anticline, Lali, is about 17 meters in the 10-year period of drought. The main reason for the difference between the hydrogeological behaviors of these two regions is related to the different lithology of the Ilam and Sarvak formations, the thickness of the layers, and the different fragility properties of these two formations in the two regions, which creates a karstic aquifer with a very good potential in the Lali area

Due to the drought and land use changes in recent years, the phenomenon of storm dust in Iran is increasing as a dangerous environment. Dust influences climate change and human health, causing serious damage. The subject of this research is to identify and prepare a map of sensitivity of dust source area for controlling and determining the role of each of the factors affecting its occurrence using the regression tree data mining model (BRT) in eastern Iran. For this purpose, at first 147 dust source area were identified in the region and divided into two groups for modeling and evaluation. According to the studies, eight effective factors including land use, geology, slope degree, elevation, normalized vegetation index (NDVI), distance from the river, wind speed and rainfall were identified and the layers of these factors were prepared in GIS environment. To evaluate the results, the ROC curve was used. The results showed that the BRT model with the area under the curve (79.6) had a good performance in producing a dust sensitivity map in the study area. Based on the results of the model, vegetation index, elevation and slope had the most impact on the occurrence of dust in the region.

Drought is one of the most prevalent and dangerous disturbances around the world, which cause significant economic and agricultural losses. Kerman province located in the center of Iran is in the first places of drought. The purpose of this research was to investigate the meteorological and hydrological drought condition of the study area. The relationship between meteorological and hydrological drought was also investigated. For this propose, 11 hydrometric stations and 10 precipitation hydrometric stations were extracted. The hydrological and drought indicators were measured using SPI and SRI were calculated at different time scales. Then, the relationship between meteorological drought and hydrological drought, as well as the relationship between meteorological drought with hydrological drought occurring with different time delays, were analyzed using Pearson correlation. The comparison between SPI and SRI indexes showed that in all meteorological stations, drought periods have increased since 2000. The highest correlation between these two types of droughts in the region was related to 48 month periods. The results showed that hydrological drought severity is more than meteorological drought in the region. At the beginning of the study period, meteorological droughts have not an important different with hydrological droughts; however, since the year 2004, the severity of hydrological drought has increased continuously in the region. The correlation between SPI and SRI index at different stations was not the same. The results of the Pearson correlation between SPI and SRI index with delay of 1, 2, 3 and 4 months showed that the highest correlation between SPI and SRI were occurred for the same period. These results also indicate that meteorological droughts immediately affect the river flow and consequently, the hydrological drought was happened

Among the global issues, climate change, desertification, and water shortage are the three major crises in the 21st century. Desertification is challenged universally and its consequences are threatening human life and natural ecosystems. Desertification, the process of land degradation in arid and semi-arid lands, is one of the most complicated problems that can occur globally, regionally and nationally scales. Some of the effective factors on desertification include climate change, overgrazing, over-drafting of groundwater, deforestation, over-exploitation of natural lands which varies from region to region. According to reports, approximately 80% of Iran is located in the arid and semi-arid area and approximately 35 % of this area is prone to desertification. On the other side, to achieve sustainable development, the evaluation of desertification risk and its vulnerability is needed to be used as an effective tool for assessing qualitative and quantitative aspects of desert lands. This will help planners identify the critical points to guide them toward the low-risk areas and also to prevent the waste of facilities and limited resources. For this purpose, it is necessary to recognize the desertification indicators to provide a model for assessment of the desertification severity and its risk. This study was aimed to investigate the desertification hazard and its risk in Bashtin, Sabzevar by the Topsis-GIS method. 

 For modeling, the spatial distribution of desertification risk in Bashtin, Sabzevar, the TOPSIS, and GIS models were used. The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) is a multi-criteria decision analysis method, which was originally developed by Hwang and Yoon in 1981 with further developments by Yoon in 1987, and Hwang, Lai and Liu in 1993. The TOPSIS concept is based on the shortest geometric distance from the positive ideal solution (PIS) and the longest geometric distance from the negative ideal solution (NIS). In this study, the principal indices of desertification were determined, and the effective indicators in Bashtin, Sabzevar were chosen among the different indices identified for the desertification phenomenon. To complete the desertification hazard assessment, the IMDPA model parameters were given to the experts' group consisting of nine experts and six parameters (geology, dryness, annual precipitation, soil salinity, soil texture and the percentage of vegetation) were selected, using Delphi and AHP methods. Also, the elements at risk and their vulnerability were prepared, and finally the risk map was established upon them. To assess the risk of desertification, each indicator was classified and standardized based on the IMPDA model using ArcGIS software. The indices were weighted by the use of the Analytical Hierarchy Process (AHP). To integrate the standardized maps and calculate desertification risk, the TOPSIS techniques and GIS operators were used. The desertification risk in the study area was achieved using the following equation: R=H×E×V, where: H: is the desertification hazard, E: the elements at risk and V: the vulnerability map at each pixel in the raster that is formed.

 The results showed that the soil and water salinity were the most effective factors in the desertification of Bashtin. Most of the region classified into the hazard class II (35/54%) and the minimum of the area is located in class I (8/05%). Critical classes of desertification hazard (IV and V) cover 50% of the area. These areas are mostly located near Kal-e Shour and in the southern agricultural lands of the city. Also, Most of the region (56/68%) is classified into the risk class II. The statistical analysis shows a statistically significant difference (at a level of 99%) between the spatial distribution of risk and hazard classes in the Bashtin region.

Based on the desertification risk map, it can be concluded that most of the area is located in the moderate class of desertification risk. According to the findings, the villages, roads, and wells are at higher risk of desertification. Upon the obtained results, the western part of Sabzevar city along the Sabzevar-Tehran road was classified into a severe risk of desertification. This is due to the high vulnerability of risk elements with severe hazard class that has increased in the risk class which led to the critical condition of desertification. In this regard, the desertification risk map can be used to prioritize the Bashtin area to de-desertification programs.

Sustainable development of agriculture is facing with several challenges such as climate change resulting change in the pattern of weather parameters as well as crop water requirements. In this research, due to the important role of agricultural activities whitin Urmia Lake Basin in the production of various agricultural products such as wheat, the possibility of supplying the plant's water requirement from green water and drought and evapotranspiration (ET) changes under climate change were investigated. Using the SDSM model and baseline meteorological data (1967-2015) of Tabriz and Urmia stations, meteorological data for the future period (2016-2100) was projected under RCP2.6 and RCP8.5 scenarios. Reference ET and the severity of drought were assessed by using the FAO-Penman-Monteith equation and the SPI drought index, respectively. The SDSM model had a relatively good performance and accuracy in estimating rainfall and ET in the study area. The findings of the study indicated an increase of 63 and 3% in the average rainfall of the future period for Tabriz and Urmia stations, respectively, and a reduction in severity of drought compared with baseline period. Under climate change, the average of annual ET of Tabriz and Urmia stationswill be decreased by 3 and 1.5%, respectively, and the amount of green water will be increased.

Evaluation of Earth Fissures Caused by Land Subsidence in Kashmar-Bardaskan Plain,NortheastIran