Farshad Pazhooh; Farzaneh Jafari
Abstract
Extended Abstract
Introduction
Due to its specific geographical situation,Iranhas an especial precipitation pattern. In other words,despitehaving a precipitation equal to one-third of global average,Iran experiences a strong fluctuation in its rainfall regime. According to global classifications, floods ...
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Extended Abstract
Introduction
Due to its specific geographical situation,Iranhas an especial precipitation pattern. In other words,despitehaving a precipitation equal to one-third of global average,Iran experiences a strong fluctuation in its rainfall regime. According to global classifications, floods are considered to be among the most important natural disasters. In recent decades, humaninterferencesin the environment and improper management of land usehave resulted in increasing severity and higher frequency of these natural disasters (Abbas ZadehTehrani et al., 2010: 78). Extreme floodingcaused by climate changeshave resulted in severe damages in different parts of the world during recent decades and the effects of these changes are more significant in dry environments (Negaresh et. al., 2013: 15). Increasing urbanization and constructions has naturally reduced permeable areasin different basins. The resulting impenetrable surfacesare incapable of absorbing the rainfall, and consequently, the total volume of runoff in the city has increased (TaheriBehbahani and Big Zadeh, 1996).
Materials and methods
Two typesofground level data and data collected from higher levels of the atmosphere were used in the present study:
A) Precipitation data collected during the first ten daysof April 2019 by stations in Western and South Western Iran obtained from the Iranian meteorological organization.
B) Data collected from higher levels of the atmosphere including revised geopotential heights, sea level pressure, meridian and orbital winds, omega and especial humidityobtainedfrom the National centre for environmental surveys at Colorado, USA.
For synoptic analysis, environment to circulation approach was used to detect heavy rainfall peak periods and then their synoptic dimensions were reanalysed in the spatial range of 10 to 70 degrees north latitude and 10 to 80 degrees east longitude. Based on the analysis ofprecipitation data, April5th and11th,2019 were selected as having the highest rainfall resulting in the highest level of flooding and damage in the western and southwest regions of Iran.
Results and Discussion
On April 5th,2019 most regions of Iran have receiveda rainfall of more than 20 mm. The maximum levels of rainfall wererecorded in Koohrangstation(187 mm), Izehstationin Khuzestan (155 mm) and Yasoujstation(151 mm). OnlySistan and Baluchestan, Kerman and South Khorasan Province have experienced a stable situation without any precipitation on this day. However, on April 11th,2019, the highest level of rainfall has occurred inwestern stations of the country. The maximumlevels of rainfallon this day were recorded inNahavand and Tuyserkan stations (Hamedan Province) and Noorabad(LorestanProvince) with 126 and 122 mm, respectively. Central and northwesternregions of the country have experienced the next highest level of rainfallfollowing western regions. Figures 1 to 3 show a part of precipitation values in the western and southwestern regions of Iran during rainfall peak periods. Precipitations in more than 16 provinces in the western, southwestern, and central regions of the country have damagedagricultural, economic and social sectors. More than 45 people were killed in thesedays.The highest number of deaths and injurieshas occurred in Shiraz. In the western parts of the country, Poldokhtar and Mamoualn were most severely damaged. Moreover, heavy rainfall and floodinghave damaged 700 thousand hectares of agricultural land and resulted in 4600 billion USDlosses. In the construction sector, the country has suffered from 1,600 billion USD losses (Hamshahri Newspaper, 1398).
Conclusion
The present study have focused on synoptic and thermodynamic analysis of systems causing pervasive, heavy and hazardous precipitation onApril 5th and 11th in the western and south western regions of the country. The synoptic and thermodynamic analysis of maps indicated that the contrast between the influence of southern and western low pressure fronts such as Saudi Arabia, Sudan and the Mediterranean on the southwestern areas of the country and the cold high pressure frontover the Caspian Sea have caused a strong pressure gradientand formed a strong front condition over the country and the region under study at the sea level. In the middle and upper atmosphere, deep multiple amplitudetroughsformed over the North Pole passed through Russia as bipolar and low pressureblocks, cyclonic centressettled over the eastern Mediterranean regions and the eastern half of the trough formed as a result of blocking settledover the western and southwesternregions of the country. These have resulted in severe, and widespread negative omega and divergence of warm and humid southern weather over the country and the region.
Hasan Lashgari; Hooshang Ghaemi; Fatemeh Parak
Volume 22, SEPEHR , April 2013, , Pages 57-63
Abstract
Precipitation is the first important parameter in studying dry and wet years. It has a direct relation with precipitation systems entering Iran and the sources of humidity which inject humidity into those systems. Studies performed on Sudanese system indicate that precipitation in southern parts of the ...
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Precipitation is the first important parameter in studying dry and wet years. It has a direct relation with precipitation systems entering Iran and the sources of humidity which inject humidity into those systems. Studies performed on Sudanese system indicate that precipitation in southern parts of the country have a close relation with the activities of this system in cold days of the year and it plays the most important role in heavy rainfalls. Reviewing synoptic maps of high and low precipitation reveals that two different dominating patterns exist in the area. In the high precipitation pattern, Sudanese low pressure is located on the South West of the Red Sea and continues toward North East and influences South and South West of Iran. This pattern dominates South East of the Arabian Peninsula. It inject heat and humidity from the Oman Sea and the Arabian Sea on one hand and the Adan Gulf and the Red Sea on the other hand to the mentioned systems. Then, this heat and humidity enters Iran Southern area with the Sudanese system. Due to the deepening of east Mediterranean trough, and the falling of cold weather from eastern latitudes in the Sudanese system, the system becomes extremely powerful and changes into dynamic status, creating a heavy rainfall on the area. In the weak precipitation pattern, Sudanese low pressure system is extremely weak and it crosses the southern areas of the Arabian Peninsula in east-west direction. Moreover in this pattern, a cyclone system covers South Eastern areas of the Arabian Peninsula.