Floods become the main threat to coastal Sahara

September 10 () –

Increased soil erosion in coastal areas due to desertification is worsening the impacts of flooding in port cities in the Middle East and North Africa.

An international team of researchers focused their observations in the devastating 2023 floods in the city of Derna, Libya, which claimed the lives of more than 11,300 people and showed how increased soil erosion contributed significantly to the catastrophic cost of these unusual desert floods.

The research, published in Nature Communicationswas published nearly a year after the deadly flood occurred on September 10, 2023. The co-authors believe their work sheds light on the alarming vulnerability that drylands face given the increasing frequency of extreme weather events due to climate change and the urgent need for advanced Earth observation programs to monitor and characterize these areas.

Over the past decade, the Sahara Desert, an area larger than the continental United States, has faced a dangerous combination of conditions: increasingly arid conditions punctuated by intense coastal storms.

The source of these changes is as follows: increasing desertification has led to intensified droughts and rainstorms in the region have increased in frequency due to rising sea water temperatures in the eastern Mediterranean due to global warming.

The paper’s corresponding author, Essam Heggy, who is a research scientist at the USC Viterbi Center for Aggregates and Water Research and Exploration (AWARE), says that together, these two extreme conditions are increasing soil erosion and generating deadly mudflows that are difficult to control with the aging dams in the area.

While some academics believe droughts are the Sahara’s deadliest threat, Heggy warns in a statement that this is not the case as the new research has provided evidence that they are floods.

AFRICA’S DEADLIEST FLOOD IN A CENTURY HAPPENED IN THE DESERT

One year ago, in the fall of 2023, Storm Daniel, also known as “Medicane Daniel,” struck the eastern coast of Libya, causing unprecedented flash flooding that killed more than 11,300 people and caused large-scale damage to infrastructure. (Yale Climate Connections has suggested that flash flooding of this nature has not been observed on the continent in more than 100 years.)

The authors explain that Africa’s deadliest flood in a century, which occurred in the desert, It occurred due to a combination of factors: unusually high rainfall, collapses of two flood control dams, and the failure of the city’s “blue” or water infrastructure to regulate this extreme event.

Researchers suggest that sediment loading, resulting from surface erosion, increased the density of flowing water and exacerbated the catastrophic impact of flash flooding in the coastal cities of Derna and Susah, where 66% of urban surfaces in Derna and 48% in Susah suffered moderate to severe damage.

Using a series of images from Sentinel-1A’s C-band synthetic aperture radar, the researchers measured changes in the coherence of the returning signal, which reported changes in surface texture properties before and after the storm occurred. (These differences serve as a proxy for mapping flood erosion and assessing damage to infrastructure.)

The researchers showed that the flow within the streams was heavily loaded and thickened with eroded soils which increased the destructive nature of the flow. This, in turn, contributed to the failure of two dams that were supposed to protect the city and residents of Derna.

Existing runoff flow models are valuable for estimating the extent of flooding, says Heggy. However, he says they are not sufficient for assessing surface erosion in deserts, which can have a devastating impact, as seen in Derna.

Radar satellites, says Heggy, overcome this limitation. “Improving monitoring of arid watersheds using advanced radar satellites will be crucial.” to mitigate these devastating risks in several parts of the Sahara, the Arabian Peninsula and other deserts“.