Sciency Thoughts: Flooding kills over a hundred people in northern Afghanistan.

Wednesday, 2 September 2020

Flooding kills over a hundred people in northern Afghanistan.

A total of 116 people have now been confirmed dead and 120 injured, with many more missing, following a series of flash floods around the city of Charikar in Parwan Province in northern Afghanistan on Tuesday 25-Wednesday 26 August 2020. The incidents were triggered by heavy rainfall associated with the region's annual monsoon season, and hit largely new housing developments that have sprung up informally in the last 30 years, when there has been little organised planning in the country, resulting in the possibility of such events not being taken into account during the construction process.

Damage caused by flash flooding around Charikar in Parwan Province in northern Afghanistan in the last week of August 2020. Jawad Jalali/EPA/Shutterstock.

Flash floods and landslides are a frequent problem in northern Afghanistan, where a mostly dry climate is broken by occasional bouts of heavy rainfall. The dry nature of the climate means that little of the landscape is covered by extensive vegetation (which can stabilise hillsides with root-growth), making the area vulnerable to flash floods. This situation is made worse by the widespread use of dried mud bricks as a building material, resulting in buildings that offer little protection against flooding and are easily swept away.

Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate. This situation is particularly intense in South Asia, due to the presence of the Himalayas. High mountain ranges tend to force winds hitting them upwards, which amplifies the South Asian Summer Monsoon, with higher winds leading to more upward air movement, thus drawing in further air from the sea.