Flooding in the desert, an increasingly frequent mortal danger
Researchers from the University of Southern California and the IPGP have revealed that hydroclimatic changes in North Africa due to global warming are increasing soil erosion factors, amplifying the effects of flooding in desert regions and generating mudflows that are heavily laden with sediment, as during the Daniel storm in Libya in 2023.
Left: conceptual detection of soil erosion in the Derna watershed using Synthetic Aperture Radar coherence. Right: damaged area in the city of Derna as measured from Synthetic Aperture Radar.
On 10 September 2023, storm Daniel hit the east coast of Libya, causing unprecedented flash floods and resulting in the deaths of more than 1,300 people, as well as extensive material damage. Africa had not experienced a natural disaster on this scale for over a hundred years, the paradox being that these deadly floods occurred in the middle of the desert and in the driest country on the continent.
Over the past decade, the Sahara has been confronted with a dangerous mix of climate changes. Increasingly severe droughts have aggravated desertification and reduced the area of vegetation cover, while the frequency of rainstorms has intensified, due to the rise in water temperature in the eastern basin of the Mediterranean Sea caused by global warming.
A team of researchers from the University of Southern California and the IPGP have revealed that these combined hydroclimatic conditions increase soil erosion factors, amplify the effects of flooding in desert regions, particularly in North Africa, and generate mudflows that are heavily laden with sediment.
Using a series of radar images acquired by ESA’s Sentinel 1A satellite at the time of Storm Daniel, the scientists show that the flow of sediment into the valleys of the Derna basin was heavily laden with mud due to the increasing rate of soil erosion, exacerbating the destructive nature of the floods. This phenomenon also contributed to the failure of two poorly maintained dams that were supposed to protect the city of Derna, combined with the inability of the city’s hydraulic infrastructure to manage the flow of these sediment-laden floods. As a result, 66% of Derna and 48% of Soussa suffered significant damage.
This study highlights the increase in water-related natural disasters such as storms, floods and drought, and the increased vulnerability of coastal catchment areas in the arid southern Mediterranean as a result of climate change. The implementation of programmes to monitor these risks and a transformative coastal management approach is urgently needed in North Africa.
« The deadly floods in Derna show that a number of countries have yet to wake up to the warnings from the scientific community about the hydroclimatic changes underway, despite hosting the last two UNCC climate summits in the region. The most formidable enemy for the future is our belief that these extreme phenomena are just passing events that will not recur. Hydroclimatic models tell us that they will strike with greater intensity »
Essam Heggy
Researcher at the University of Southern California
Ref: J.C.L. Normand & E. Heggy, Assessing flash flood erosion following storm Daniel in Libya. Nature Communications 15, 6493 (2024). DOI: 10.1038/s41467-024-49699-8
