Sunday 21 October 2018

Flooding causes severe disruption in Qatar.

The city of Doha in Qatar has suffered severe disruption to transport networks and other services, after receiving almost a year's rainfall in a day on Saturday 20 October 2018. A total of 61.1 mm had fallen by early evening, against a yearly average of 77 mm, leading to many roads being flooded and impassable, and local authorities issuing warnings against people entering the city's many road underpasses due to the risks of becoming trapped. A number of public buildings have been forced to close their doors due to the flooding, including the National Library and the US Embassy.

Flooding in Doha, Qatar, on 20 October 2018. I Love Qatar.

Qatar has been widely reported as having received almost than an average years rainfall within 24 hours, about 61 mm compared to 75 mm, though this is slightly misleading as Qatar does not receive any rain some years, lowering the average rainfall, and what does fall often arrives in the form of sudden extreme downpours. Flash floods are a common problem in Qatar (and other areas with a dry climate) as protracted periods of dry weather can cause topsoil to dry out completely, making it vulnerable to being blown away by the wind. When rain does arrive it then falls on exposed bedrock, which is much less absorbent, triggering flash flooding as the water escapes over the surface of the ground rather than sinking into it. These floods wash away more topsoil, making the problem progressively worse over time.

This extreme weather is thought to be connected with a developing El Niño weather system, which warms the waters of the Arabian Sea by around. This warming leads to higher rates of seawater evaporation, i.e. more water entering the atmosphere over the ocean, which in turn leads to more rainfall on land.

The El Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of El Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe El Niño conditions, extreme weather conditions a common occurrence.

Movements of air masses and changes in precipitation in an El Niño weather system. Fiona Martin/NOAA.

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