An endorheic basin is defined as a region in which the river network is completely isolated from the world ocean: the water flowing in the rivers never reaches the sea. Still poorly studied, these regions cover about 20% of the continental surfaces. They are mainly localized in arid and semi-arid areas and represent about half of the water-stressed regions.
Total terrestrial water storage in endorheic basins: in red, basins that are loosing water, in blue those that are gaining water (from Wang et al., Nature Geoscience, 2018, https://doi.org/10.1038/s41561-018-0265-7)
Emblematic examples are the Aral Sea basin in Central Asia, the Central Kalahari basin in Southern Africa or the paleo Niger delta in Northern Africa. Due to their isolation, endorheic basins represent unique geo-ecosystems, delicately balanced through a tight coupling between climatic, topographic, ecologic and geologic settings. From there, a slight modification of the environment can dramatically affect the fragile equilibrium of these hot-spots of biodiversity, especially in semi-arid or arid climate contexts. Such imbalance events are largely suspected to be a major factor in the evolution of biological species (including human evolution) and societies. However, the kinetics of changes and the respective influence of each forcing factors remain unknown due to the lack of integrative study. Still, these parameters are of primary importance to recognize, explain and quantify the past biological and civilization crisis. Moreover, an integrated understanding of all processes acting upon such fragile ecosystems is urgently needed to forecast upcoming changes and adapt ecosystems preservation policies or potential economic consequences. Indeed, the faith of the emblematic endorheic Aral Sea highlighted the short-term fragility of such geo-ecosystems and the strong impact that anthropic activities associated to global changes may have on their sensitive equilibrium.
The decline of the Aral sea in Kazakhstan and Ouzbekistan. The pumping of water in the Amou-Daria and Syr-Daria rivers for agricultural purposes (mostly coton production) lead to a near complete drying up of the once world 4th largest lake (Landsat images).