عنوان مقاله [English]
The occurrence of drought in Sistan region and consequently the entry of sediments into the water reservoirs of semi-wells has provided favorable conditions for the formation of dust storms and has caused great damage to the natural and human life of the region. One of the important objectives of this study is to investigate the destructive effects of droughts on the region, especially on Chahnimeh. The studies performed in this study include the use of physical and chemical analysis methods of samples to determine statistical parameters and use its results in interpreting the transport and sedimentation conditions of particles, determining critical foci of wind erosion, drawing curves Granulation and interpretation of multiple phases of the samples, which together with the results of the study of sediments in the desired location, leads to determining the type of sedimentation environment and determining the origin. Drought analysis using five indices of normal percentage of precipitation (PNPI), standardized Z criterion (ZI), precipitation amplification classification (PC), mean deviation (SDI) and precipitation anomaly (RAI), on seasonal precipitation information and statistics And four synoptic stations were performed annually in Zabol, Zahak, Hirmand, Hamoon. The results showed that the index (SDI) compared to PNPI, ZI, Sd and RAI methods on a seasonal and annual scale provided more acceptable estimates. Zabol has experienced droughts on a seasonal and annual basis based on the SDI. The highest frequency of drought in spring is from the index (PC) and in summer is related to PNPI, ZI, Sd and RAI indices. On an annual scale, the highest and lowest frequency estimates were observed with 64% and 41%, respectively, in the PC and PNPI method indices. The origin of sediments in the wells is based on the results of the erosive winds in the region, which are north to northwest with an angle of 330 to 360 degrees (120-day wind in Sistan) and the most important harvest facies, abandoned lands, sandy lands and areas they are the bedrock of Hamoon Lake and the northern plains.
Drought is a natural phenomenon of ecosystems that can occur in any region and have major impacts on that region (Freire et al, 2019). Drought is one of the most important natural disasters that causes a lot of damage to agriculture and water resources (Pirmoradian et al. 2008). In addition, this phenomenon is called calm and creeping phenomenon. For this reason, drought is said to be more complex than other natural disasters in that it covers a wider area. In other words, it is the most costly (Fontaine et al, 2009 is a natural disaster in terms of reduced agricultural production and the suffering of farmers. (Downing and Bakker, 2019). Occurrence of drought in Sistan region and consequently decrease of vegetation and drying of Hamoon Lake as well as 120-day winds, have provided suitable conditions for wind erosion and occurrence of dust storms. The chahnimeh are large natural pits at a distance of 50 km from the city of Zabol, to which the excess water of the Helmand River is directed through a canal. These pits are organized to store water and are drained from two Helmand branches with an area of one canal. ChahNimeh water reservoirs, which are the only source of drinking water for the people of Sistan, will be seriously threatened by quicksand in the next few years, and if the influx of sand into these reservoirs is not prevented, the life of this important and very sensitive water source in the region will be endangered. In Sistan region, in a period of almost 30 years, in 1318, 1328, 1337 and 1349, ie almost every 10 years, a drought has been fatally repeated and since 1997, this region has experienced the effects of the recent drought. Bears. Studies show that 14 provinces of the country are affected by wind erosion, of which Sistan and Baluchestan province with 229174 hectares has the highest rank (Iranmanesh et al., 2005). Undoubtedly, the main cause of wind erosion in the study area is the occurrence of sandstorms due to 120-day winds in Sistan. During the last two centuries and especially in the last few decades, destructive and harmful effects have entered the human environment and due to the misuse of natural resources, deserts have expanded rapidly (Ahmadian, 1999). According to the estimation of the wind potential intensity in 60 meteorological stations of the country, Zabol station has the highest frequency and speed. This region is also the second largest occurrence of sandstorms in Asia with an average of 80.7 days per year over a five-year period (1990-1995) (General Department of Natural Resources of Sistan and Baluchestan Province, 2004).
In order to conduct this research, first, with direct field observations and field operations, to determine the harvest areas, the sediments in the chahnimeh, transport areas and possible harvest areas were sampled and based on mineralogical characteristics and study. The genetic relationship of the samples to the primary origin of the sediments was investigated. In order to identify the harvest areas, sampling was done from the sand accumulation site, from different points around the reservoirs and from possible harvest areas, and the genetic relationship (similar properties) of the three areas (harvest, transport and sedimentation) was analyzed. Physical and chemical sediments were studied. Also, four synoptic stations (Zabol-Zahak-Helmand-Hamoon) were studied for this research. In order to analyze the seasonal and annual drought, five indices of normal percentage of rainfall (PNPI), standardized Z criterion (ZI), precipitation amplification classification (PC), mean deviation (SDI) and precipitation anomaly (RAI) are used.
Drought is an exceptional and unfortunate event that always changes human, plant and environmental ecology in general. Field studies have shown that in the last few years drought, the movement of sand dunes has been so great that it has caused the burial of a large number of residential houses and the invasion of agricultural lands. The damage to water supply facilities and canals is not less than other centers, so that compensating for all this damage will impose a lot of cost and time on society.