Lake Chad hydrological cycle under current climate change
Résumé
In a near future, the Sahara and Sahelian regions could experience more rainfall than today as aresult of climate change. Wetter conditions in the hottest and driest place of the planet today raisethe question of whether the near future might hold in store environmental transformations,particularly in view of the growing human-induced climate, land-use and land-cover changes.Reflecting an enhancement of the global hydrological cycle under warmer conditions, someexperiments provide support for the notion of a strengthening of the monsoon in the future andmore rainfall in central Sahel and Sahara. However, some remote forcing could counterbalancethe decadal trend. Modeling experiments suggest that the freshwater discharge coming fromGreenland melting could significantly impact the sea surface temperature of North Atlantic andinduce a decrease in Sahel rainfall for the next decades, remaining left open the question howSahara will be in a warmer climate?By chance, Lake Chad, located at the southern edge of the Sahara, is recognized for being the bestsite in Africa for deciphering hydrological and climate change. After being ranked at the world’ssixth largest inland water body with an open water area of 25,000 km2 in the 1960s, it shrunkdramatically at the beginning of the 1970s and reached less than 2000 km2 during the 1980s,decreasing by more 90% in area. Because it provides food and water to 50 millions of people, itbecomes crucial to observe precisely its hydrological cycle during the last 20 years.Here by using a new multi-satellite approach combined with ground-based observations, we showthat Lake Chad extent has remained stable during the last two decades, slightly increasing at14,000 km2. We extend further this reconstruction by adding new data from the hydrological year2019-2020, which is considered at an extreme in precipitation recorded over the Sahel. Moreover,since the 2000s, groundwater which contributes to 70% of Lake Chad’s annual water storage, isincreasing due to water supply provide by its two main tributaries draining a catchment area610,000 km2 wide. Because the current climate change seems to be characterize by a higher
interannual variability affecting from year to year the amount of precipitation during the rainyseason and increasing the vulnerability of the economy of the region mainly based of agropastoralactivities, we investigate the yearly cycle and see how it is impacted the hydrological cycle of LakeChad and changed over time.