نوع مقاله : مقاله مستخرج از رساله دکتری
1 دانشجوی دکترای اقلیم، دانشگاه تربیت مدرس، تهران، ایران.
2 دانشیار اقلیم، دانشگاه تربیت مدرس، تهران، ایران.
3 استاد اقلیم، دانشگاه تربیت مدرس، تهران، ایران.
عنوان مقاله [English]
Drought is a normal fact of temporal and spatial fluctuations of climate and can occur in any type of climate. Drought is a persistent and abnormal lack of moisture over a period of time, usually one year. In this definition, the word continuous refers to the persistence of a state of deficiency and the word abnormal refers to the deviation of the desired index from the normal (average) conditions. This phenomenon, as a natural disaster and an inevitable phenomenon, has been occurring in a wide range of countries for a long time. Studies show that the West Asian region, due to its geographical and climatic conditions, like many countries in the world, especially North Africa is not in a good position in terms of water supply.
In this study, SPEI networked data with a spatial resolution of 0.5 by 0.5 degrees; Used over a statistical period of 118 years (1901-2018). This index is a relatively new index of drought and is based on the developed SPI. In this study, first, drought critical points were estimated and calculated for each of the time periods of 1, 3, 6, 9, 12 months, and after extracting the critical points, taking into account the geographical coordinates of the points in the networked data, The point of the main network was extracted and after extracting the data of each point which included 1416 months during the 118 years of the statistical period, the time trend of the critical network points was analyzed. Extensive critical points of severe and extensive droughts have been extracted from long-term cumulative maps (ASPEI) of the study area, which are in fact the negative accumulation of SPEI in each time period of the study period of 118 years. After drawing ASPEI maps for each time period of SPEI, two critical points are identified and the trend of their time changes is examined.
Results and Discussion
The results and findings of the study show that based on negative ASPEI values, critical areas of one-month drought are visible in the Arabian Peninsula and Yemen, as well as in the southern regions of Iran. The largest widespread and severe one-month long-term droughts occurred in western and central Saudi Arabia, all of Yemen, southwestern Oman, and southern Iran. Drought is more severe in central Yemen and western Saudi Arabia. During the quarter, critical areas on the Arabian Peninsula in Saudi Arabia and Yemen, as well as in southern Iran and parts of southern and eastern Iraq, central Afghanistan and northwest They are from Turkmenistan. Areas of severe crisis in Yemen and western Saudi Arabia. The largest widespread and severe long-term quarterly droughts occurred in western Saudi Arabia, all of Yemen, southwestern Oman, and southern Iran. Drought is intensifying in central Yemen and western Saudi Arabia. The six-month drought is visible on the Arabian Peninsula in Saudi Arabia and Yemen, as well as in southern Iran and parts of southern and eastern Iraq, central Afghanistan, and northwestern Turkmenistan. The largest widespread and severe long-term six-month droughts occurred in western Saudi Arabia, all of Yemen, southwestern Oman, and southern Iran. Drought is intensifying in central Yemen and western Saudi Arabia. The severity of the 12-month drought is visible in Yemen and southern Iran, as well as in parts of southern and eastern Iraq, Turkey, Saudi Arabia, Afghanistan, and northwestern Turkmenistan. The largest widespread and severe 12-month long-term droughts occurred in western Saudi Arabia, all of Yemen, southwestern Oman, and southern Iran. Drought is more severe in central Yemen and southern Iran. The Kendall Man test for these areas, as shown in the table, indicates a significant and continuous trend of occurrence and intensification of droughts in the study period and in the future.
The study of drought change based on climate change is important from various aspects. This study was conducted to estimate and calculate the drought critical points for each of the time periods of 1, 3, 6, 9, 12 months and the time trend of the critical network points during a statistical period of 118 years (1901-2018). According to the results obtained in the study area, the greatest impact of drought in Yemen has been the central and southern parts of Iran and the west and Saudi Arabia. So that in all long-term periods, the main and severe drought is seen in these areas. Also, some regions of Iran, such as the western, eastern and southeastern regions, have been affected by severe droughts. In Yemen and western Oman, the drought situation is visible in all long-term periods, and in Iraq, except in the one-month period, and the whole drought core is concentrated in eastern Iraq. Turkey, Turkmenistan, Pakistan and Afghanistan are also experiencing limited drought. In the mentioned countries, western and southern regions of Turkey; Northwestern region of Turkmenistan; The western regions of Pakistan and Afghanistan are more affected by drought than any other region. Only 12 months of drought is observed in Azerbaijan. But in Armenia we do not see drought in any of the periods. According to the spatial map of 12-month periods, it can be seen that the severity of droughts has decreased, but the area of drought-affected areas has increased significantly. Due to the selection of hotspot areas from different areas of the region, we saw the trend of increasing droughts during the study period. Although this trend has increased slightly until the 1990s, it has been high in the last two decades. This (increasing) trend is observed in all identified areas.