Today I want to focus on a specific paper by Favreau et al (2009) that explores how land-cover change and climate change affect water resources in conjunction in semi-arid Africa.
I found this to be extremely interesting, as findings here suggest that a change in the land use and resulting changes in the soil cover, can eliminate the pressures on water resources expected under decreased monsoonal rainfall and higher temperatures.
The area under study (southwest Niger) underwent a large scale land-cover change from natural savannah to millet crops - which dramatically altered the local water balance. Surface crusting of the soil meant that there was an increased occurrence of gullys and ponds in the landscape, fed by in increase in Hortonian overland flow on slopes. These ponds are points of focussed groundwater recharge to the underlying aquifer. A physically based, distributed hydrological model quantified the change: while the adverse effects of climate change had reduced runoff by 2 fold, the change in land cover had increased it by 3 fold, resulting in a net increase. A different modelling approach on the wider regional area analysed groundwater table fluctuations and related the evolution of land use to an increase in recharge from 2mm/yr to 25mm/yr (+/- 7mm).
This "Sahelian paradox" highlights that issues of water in Africa need to be examined on the ground - and that a predicted decrease in rainfall (here 23% reduction in mean annual rainfall, 1970 – 1998 versus 1950– 1969) does not equal to a reduction in water availability. In fact, human alterations of the natural systems (climate and land cover) here increase the water resources regionally.
I haven't heard of this before, a great example of how relationships are much more complex than they appear in the real world! Wouldn't think water would increase with decreased rainfall!
ReplyDeleteThanks for the comment!
ReplyDeleteVery true - This is exactly what lots of policy neglects! The climate change induced changes in precipitation are greater in their effect on variability throughout the year than the actual lump sum per year! The increased seasonality and intensity has very different effects depending on the ground geology and land cover. I think this highlights the need for more continuous and detailed ground-research to predict the impact with greater certainty!