عنوان مقاله [English]
Drought is an inseparable phenomenon of climate in any geographical region. But it may have different behavior and different environmental effects with the change of geographical environment. Vulnerable environments will suffer more damage. As a result, to the extent that our understanding of the behavior of this phenomenon is more accurate, we will have a more appropriate behavior and reaction. Adaptive behavior will cause us to have less damage from environmental hazards. During the occurrence of droughts, some features of the rainfall element such as intensity, intervals of rainfall days, number of rainfall days, length of rainfall period, etc. will experience severe abnormalities. The occurrence of abnormality in the normal behavior of precipitations leads to a change in the hydrological behavior of the environment and changes all the elements and factors related to precipitation. The most incompatible environmental elements will suffer the most damage. The southern region of the country, due to its geographical and topographical location, adjacent to the Arabian subtropical high pressure, the hot and dry deserts in the vast expanse of the Arabian Peninsula and the Lut desert in the east and center of Iran, despite access to the moisture resources of the warm seas of Oman, Arabia and the Persian Gulf have a dry and semi-arid climate. As a result, the region inherently faces a shortage of water resources and droughts can aggravate these conditions and lead the region to a water shortage crisis.
To conduct this research, first, 34 stations from the synoptic stations of southern Iran, which had complete statistics in the years 1986-2019 (corresponding to the last three solar cycles), have been selected. The research design involves the following steps. 1- The daily and annual rainfall data of the synoptic stations of the study area were extracted from the data of the Meteorological Organization. 2- The statistical base has been chosen to adapt to the solar cycles of a 33-year period corresponding to the years 1986-2019. 3- The number of 19 synoptic stations that had these conditions were selected. 4- Wet years were determined based on standard precipitation indices (SPI), Chinese Z (CZI), Z score (ZSI). 5- To check the anomaly of precipitation RAI index is used. 6- Based on the declared indicators, with the criteria of 30% repetition in selected stations, 6 severe wet and based on 50% repetition in selected stations, three severe wets have occurred in the statistical period of 33 years. 7- In this research, two seasons of 1992-1993 and 1995-1996 have been examined in terms of anomaly indices and other rainfall characteristics.
Results and Discussion
In examining the trend of droughts in the last three solar cycles, it was observed that the frequency of years affected by droughts has increased significantly in the 23th cycle (statistical period 1997-2008) and the 24th solar cycle (2009-2019). So that out of 11 years of the 23th solar cycle, in 9 years, between one third and more than half of the study area has been affected by drought. Out of these 9 years, in 4 years there has been widespread drought. In the 24th solar cycle, out of 11 years of this cycle, in 10 of those years, parts of the studied area have experienced drought with different intensities. Of these, in 4 years there has been widespread drought. In these 4 years, more than half of the study area has been involved in severe and ultra-severe drought. Examining the abnormality created in some characteristics of precipitation showed that the intensity of precipitation has shown a sharp decrease in dry years. So that the average daily rainfall has decreased from two millimeters to less than one millimeter. Due to the temperature conditions of this region, when the rainfall intensity of the systems decreases in dry years, the effectiveness of the precipitation also decreases. In other words, a large part of the precipitation is wasted through evaporation and does not get a chance to penetrate. The investigation of rainfall anomalies also showed that the number of dry days in this region is increasing more intensively. So that in severe droughts, the number of dry days has increased to more than 350 days. When the number of dry days increases, a large part of the soil moisture is removed through evaporation and the empty spaces of the soil pores are filled with air. As a result, the little rains of dry years are not able to penetrate and are out of reach in the form of surface flows.
Drought disrupts the living conditions in all climates and makes the ecosystem face the reduction of water resources. But in dry and semi-arid climates, these effects are increasingly intensified. Because ecosystems are more vulnerable in these climates. The provinces of the southern coast of Iran, due to their port location, the presence of huge oil and petrochemical resources and industries, climatic features for the production of tropical agricultural products and the products needed by the country in the cold period of the year, are among the demographic and strategic regions of the country. Droughts and aridity in this region of the country will cause irreparable damage to the agriculture and industry of this region. Examining the trend and intensity of droughts in the last three periods of 11 years showed that the frequency of occurrence, the extent of effect and the intensity of droughts are increasing in the southern region of the country. This phenomenon has been increasing, especially in the last two solar cycles. In this way, the southern region of the country, in addition to being involved with the phenomenon of drought, the continuation of this trend will also face the region with aridity. Therefore, it is necessary for practitioners and planners to prepare the conditions for a drier climate than the current situation by redefining short and long-term goals and plans. These changes should be made especially in the pattern of cultivation of agricultural products, which has the highest water consumption in the region.