At least thirteen people have died in flooding across southern Iran between Friday 20 and Monday 23 March 2020. The worst of the flooding has been reported in Fars and Hormozgan provinces, each of which have suffered at least five casualties, Bushehr where two deaths have been confirmed, and Qom, which has also recorded a single death, but floods have also occurred in Kerman, Sistan, Baluchestan, Gilan, Kohgiluyeh & Boyer-Ahmad, and Golestan provinces. Flooding has also been recorded in neighbouring areas of Iraq and Saudi Arabia.
The Middle East, while generally arid, is prone to occasional severe flooding. This stems from two causes; firstly the arid climate prevents the development of a thick soil layer which would be expected in less dry areas, so that in much of the area (non-porous) bedrock is either exposed or close to the surface, and secondly the hot climate leads to heavy evaporation from nearby seas and oceans, so that if the wind changes direction and brings water-laden air to the area, it brings a lot of precipitation with it. This combination of heavy rainfall and low ground absorbency leads to large amounts of water at the surface, typically moving downhill at some speed. Wadis, dry channels or ravines through which these sudden floods are channelled, can be particularly dangerous at these times, particularly as they often appear to resemble natural pathways or even camp sites to people unfamiliar with the climate.
Flooding in southern Iran in March 2020. Tasnim News Agency.
The storms have been caused by a low pressure system over the eastern Mediterranean, caused by hot weather in the region, a common problem during spring in the region. As the air is heated the the air pressure drops and the air rises, causing new air to rush in from outside the forming storm zone. If this zone is sufficiently large, then it will be influenced by the Coriolis Effect, which loosely speaking means the winds closer to the equator will be faster than those further away, causing the storm to rotate, clockwise in the northern hemisphere and anticlockwise in the southern hemisphere.
Whilst the high winds associated these storms is extremely dangerous, the real danger from such storms is often the flooding. Each millibar drop in air pressure can lead to a 1 cm rise in sea level, and large storms can be accompanied by storm surges several meters high. This tends to be accompanied by high levels of rainfall, caused by water picked up by the storm while still at sea, which can lead to flooding, swollen rivers and landslides; which occur when waterlogged soils on hill slopes lose their cohesion and slump downwards, over whatever happens to be in their path.
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