Lake Chad gets talked about a lot in the environmental discussions of the Sahel.  I know little about the science. But a quick perusal of various articles by hydrologists suggests that human water management decisions (bad ones, naturally) have been a significant share of the explanation of the decrease in water contained by the lake.

Given that billions of dollars were invested in the Chad oil pipeline, and billions in revenue have been generated by the pipeline, my inclination would be to think that any “environmental” or “climate” effects of the diminished resource base due to reduced water supply, should really be thought of as “political” effects.  That is, relatively inexpensive (compared to the oil pipeline) mitigation investments could have greatly reduced the changes that have taken place in the hydrology of Lake Chad.

Over the last 40 years, Lake Chad, once the sixth largest lake in the world, has decreased by more than 90% in area. In this study, we use a hydrological model coupled with a lake/wetland algorithm to simulate the effects of lake bathymetry, human water use, and decadal climate variability on the lake’s level, surface area, and water storage. In addition to the effects of persistent droughts and increasing irrigation withdrawals on the shrinking, we find that the lake’s unique bathymetry—which allows its division into two smaller lakes—has made it more vulnerable to water loss. Unfortunately the lake’s split is favored by the 1952–2006 climatology. Failure of the lake to remerge with renewed rainfall in the 1990s following the drought years of the 1970s and 1980s is a consequence of irrigation withdrawals. Under current climate and water use, a full recovery of the lake is unlikely without an inter-basin water transfer. Breaching the barrier separating the north and south lakes would reduce the amount of supplemental water needed for recovery.

via On the causes of the shrinking of Lake Chad – Abstract – Environmental Research Letters – IOPscience.