جستجوی مقالات مرتبط با کلیدواژه « semi-arid » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Introduction :

Groundwater is one of the most important natural resources in the world. In the current situation, a significant part of Iran's consumption in the drinking sector is provided by underground water sources. In the last 20 years, salinization and reduction of groundwater quality have become one of the serious environmental problems around the world. This issue adds to the importance of proper management of groundwater consumption. Proper management of groundwater consumption is not possible without having sufficient knowledge of the distribution and expansion of saline and fresh groundwater and determining the processes influencing its evolution. Atmospheric precipitation and surface water, passing through different geological formations, dissolve the salts in them. Therefore, the chemical quality of underground water depends on the type of formation that passes through its empty spaces. Also, the time the water stays in the basement has an effective role in the quality and salinity of the water, because the longer the water stays in the sediments, the saltier it becomes.Groundwater in arid and semi-arid areas, especially in Yazd province, is the main and reliable source of water supply for various uses due to low rainfall and lack or absence of surface water sources. In order to check the condition of underground water, it is necessary to check the concentration and type of solutes in the water. One of the factors affecting the quality of underground water in Yazd province is the existence of destructive geological formations. Therefore, the purpose of this research is to investigate the relationship between the quality of underground water in Yazd province and the type of formations.

Yazd province, with an area of ​​about 737.54 square kilometers, is located in the central part of Iran's central plateau, between 29 degrees and 52 minutes to 33 degrees and 27 minutes north latitude and 52 degrees and 55 minutes to 56 degrees and 37 minutes east longitude. Yazd province is bordered by Semnan and Isfahan provinces from the north and west, Khorasan Razavi province from the northeast, Kerman and South Khorasan provinces from the east, Fars province from the southwest, and Kerman from the southeast. It varies from about 666 meters above the level of the open sea (Zarin sand desert near Aqda) to 4075 meters (Shirkoh peak). The present research is about investigating the impact of geological formations and units on the quality of underground water in Yazd province based on the statistics, information, and reports available in the Geological Organization using a 1:100000 geological map. In order to check the quality of underground water samples, 217 wells and aqueducts of Yazd Region Water Company's monitoring network in July 2013, the measured parameters of cations (sodium, potassium, calcium and magnesium), anions The main elements (bicarbonate, chloride and sulfate) present in water, electrical conductivity (EC), dissolved solids (TDS), sodium absorption ratio (SAR) and pH were used. To check the quality of underground water, sampling has been done in 18 regions of Yazd province. RockWorks 14, ArcGIS 10.3 and Excel software were used to draw and prepare maps.

To check the groundwater type of 217 sampled points in Yazd province, the average data of each region was used. By using the main ions, samples of the type of underground water in each region have been obtained in such a way that by separating the ions and their amount in each region and then implementing them in the Piper diagram, the type of groundwater in the region is obtained. As it is clear in Piper's diagram, the predominant type of underground water in Yazd province is chloride+sulfate and calcium+magnesium. These types cover the largest area in the plains and playas, which have limestone and marl. There is also carbonate type in the region due to the presence of granite formation heights that have better quality water. The interesting point in this graph is that none of the samples are in the fresh water category. The Piper diagram shows that the groundwater of the studied area is located in the hard and completely hard water type due to the existence of terrace deposits and new low-altitude foothill alluvial cones, which cover about 3,383,512 hectares of the entire area of ​​the region. According to the Wilcox diagram of the study area, C2S2 and C4S2 classes have the lowest and highest shares with 0.46 percent and C3S4 and C4S4 classes with 32.26 and 56.22 percent, respectively. According to the results of the Wilcox diagram of underground water in Yazd province, the water quality of the region is too salty and unsuitable for agricultural use. The results show that the high amount of salts is one of the problems of the water that is used for irrigation in this area. High concentration of salt in irrigation water can reduce the growth of crops or even prevent the growth of some crops, which results in soil decomposition and groundwater pollution. In such water, the growth of plants and their quality will be improved by increasing irrigation for washing or using intermittent water with low salinity and good drainage.

If there is a trend of pollution and over-harvesting of the underground water table in the region, in the next few years, with the increase of TDS in the region, the condition of the water in terms of drinking will become worse. The best quality of water for drinking is in the central and southwestern regions where the normal gneiss granite formation with eye grain structure is located in the mountainous area of Shirkoh, and the further we move away from the center, the worse the water quality is. The formation of these areas is of the type of terrace deposits and alluvial cones of new foothills.

Drought is recognized as a slow, creeping phenomenon that can accelerates the expansion of desertification in different regions especially in arid and semi-arid area with its effect on the agricultural sectors, water resources and vegetation cover. Positioning of Iran in the world arid and semi-arid belt is exposed to drought and water crisis and desertification. Drought monitoring and zoning with the goal of planning and water resources management are very important in different area especially in arid and semi-arid regions. One of the methods for drought study is monitoring and mapping of drought using meteorological indices and Geographic Information System techniques. In order to investigate and drought monitoring in present research during the period of 29 years (1989 to 2017) in Qoum-Kahak study region we used annual rainfall data from four stations (i.e. Qoume, Kahak, Koohsefid and Janatabad) which are located inside and around the Qoume-Kahak catchment. Then we applied meteorological indices such as Standard of Precipitation Index (SPI), Percent of Normal Index (PNi), Deciles Index (DI), Chinese Z Index (CZI) and Z-Score Index (ZSI) for drought monitoring during the study period. Afterward for drought mapping, four interpolation methods included Simple Kriging (SK), Ordinary Kriging (OK), Inverse Distance Weighting (IDW) and Radial Basis Functions (RBF) were used and compared. After determination of best method in each year, yearly drought map were produced based on the best interpolation methods in ArcGIS software environment. According to the result of meteorological indices the near-normal class occurred more than other classes in study stations. SPI results indicated that Jannatabad and Kahak stations have the highest and lowest frequency of extremely dry class during the study period, respectively. The most extremely dry class with the SPI of -2.35 was occurred in Janatabad station in the year of 1997-98. Based on the results of PNI and ZSI indexes there was no occurred extremely dry class in all stations. The result of PNI index indicated that Koohsefid station has the highest frequency of very dry class between all stations. According to the result of CZI index the extremely dry class was occurred only for Kahak and Janatabad stations in the water years of 2016-2017 and 1997-98 respectively. Extremely wet class was occurred also for Kahak and Janatabad stations during the water years of 2009-2010 and 1992-1993 respectively. The results of DI index illustrated that the class of very much below normal was occurred in Qoume and Koohsefid stations 4 times and in Kahak and Janatabad stations 3 times during the study period. We applied geostatistical analyst tools in ArcGIS software to produce zoning maps for rainfall and drought. Its result showed that ordinary kriging with RMSE of 28 mm is the best method to create rainfall map. Accordingly mean annual rainfall was 136 mm/year during the study period. We selected SPI index for drought monitoring and zoning because of according to the results of all meteorological indices,only for this index the extremely and severely drought classes for all stations have occurred Simultaneous with the minimal rainfall during the study period. Afterward we compared different interpolation methods to produce drought zoning maps for each year during the study period. Based on the results of RMSE ordinary kriging and simple kriging were the best methods for most years. The results of all meteorological indices suggested that in all stations the near-normal class has the most frequency during the study period. According to the results of SPI and CZI indices, the highest (7 years) and lowest (3 years) number of drought were occurred in Kahak and Jannatabad stations, respectively. While according to PN index the highest (9 years) and lowest (3 years) number of drought were observed in Qoum and Jannatabad stations, respectively. Also the results of PN index illustrated that there was no wet period during the study period. According to the ZSI Index, the extremely dry class did not occurred in the region and the ZSI results about the frequency of extremely wet class was similar to the SPI results. The results of drought zoning indicated that in the years of 1990, 1995 and 1997, most of the region has been in a state of extremely to slightly drought. In the years 2010 and 2017, slight to sever drought classes were occurred in most parts of the study area and the slight wet class was observed in the eastern part of region. While during the years of 1992, 1996 and 2009 whole of the study area has experienced moderate and severe wet conditions. In the year of 2011, half of the study area which is located in the eastern part of the region has been in a state of moderate wet condition.

Drought is one of the most costly natural hazards and is more dangerous in arid and semiarid regions which suffer from limited water resources. Climate change can also affect drought intensity; therefore, it is essential to analyze the trends of drought, particularly in these regions. This study surveyed the trends of meteorological and agricultural drought in hyper-arid, arid and semiarid regions of the world using the standardized precipitation index (SPI). Short time scales of 1-, 3- and 6-month SPI (moderate to severe and extreme drought) were derived for the period of 1970 to 2014 from the gridded precipitation data provided by CRU. The trends of the time series were computed using the Mann-Kendall nonparametric statistical test. The results showed that non-significant trends were dominant; however, some territories showed significant upward and downward SPI trends in different parts of the study regions. The significant negative SPI trends, which imply increased drought, were observed in the Middle East, central Australia and western North America. An increase in drought severity can increase consumption of water resources, particularly in developing countries.

The lack of sufficient fresh water resources, climate change and lengthy and severe droughts are of the major today’s world challenges particularly in arid and semi-arid regions. In the current conditions, especially in the case of droughts and in order to water resources planning, it is essential to analyze the changes and trends in drought particularly in hyper-arid, arid and semi-arid regions of the globe. In this study, Mann-Kendall statistics were applied to determine the significant and non-significant positive or negative trends in long term drought time series (9, 12, 18 and 24 monthly time scales) in moderate to severe and extreme classes of droughts derived based on the Standardized Precipitation Index (SPI). Results indicated the both significant positive and negative trends can be found in these regions. By increasing the time scales of droughts time series, the percentage of significant upward or downward trend grow. For example, in the case of decreasing trend of SPI (increasing in the drought), the percentage of 17.8 for 9 monthly SPI increased to 21.9, 28.48 and 31.71 for the 12, 18 and 24 monthly SPIs, respectively. The increasing in long severe and extreme classes of drought can be found in Middle East and west of America. The upward trends of drought particularly in Middle East region which is suffered by expensive tensions among the communities can intensify current critical situations. Therefore, more attention should be paid to this subject particularly in regional and international scales.