Why cutting trees in east Africa causes drought in the Sahel

And why China is damaging its farming by cutting Indochinese forests

Global tree prevalence

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Trees and water:A local story…

Local water buffering

Trees crowns buffer crops from storms, droughts

Trees roots help prevent waterlogging

Crop roots force tree roots deeper, helping shield trees from

droughts

Water buffering and woody biomass

The lower tree roots in the AF system explain why woody biomass is higher than in pure forests: the trees are less exposed to water stress.

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Trees and water:A global story too.

Dominant global winds

van der Ent RJ, Savenije HHG, Schaefli B, Steele Dunne SC, 2010. Origin and fate of ‐atmospheric moisture over continents. Water Resources Research 46, W09525,

E/P

Pfrom Et/P

P: precipitationEt: evapotranspirationE: evaporation

Much of the rain that falls on land evaporated from plants, not from the seas. Example: in the western Sahel, over 60% of rain originally evaporated from east African plants.

In much of the world, most of the water that falls as rain evaporates again through the transpiration of plants, rather than flowing to the sea. That water falls on other lands.

Rain: whence and where to?

Ellison D, Futter MN, Bishop K, 2011.On the forest cover–water yield debate: from demand- to supply-side thinking. Global Change Biology, doi: 10.1111/j.1365-2486.2011.02589.x

37% 68%58%

30%

40% 41%

46%22%

42%

1) Mackenzie river basin, 2) Mississippi river basin, 3) Amazon river basin, 4) West Afri-ca, 5) Baltics, 6) Tibet, 7) Siberia, 8) GAME (GEWEX Asian Monsoon Experiment) and 9) Huaihe river basin.

(recalculated from Basilovich et al.)

% of rain derived from plant transpiration

Sahel rains come from east Africa

Deforesting indochina will reduce rainfall in

China

Want to know more?

Ellison D, Futter MN, Bishop K, 2011.On the forest cover–water yield debate: from demand- to supply-side thinking. Global Change Biology, doi: 10.1111/j.1365-2486.2011.02589.x

van der Ent RJ, Savenije HHG, Schaefli B, Steele Dunne SC, 2010. Origin ‐and fate of atmospheric moisture over continents. Water Resources Research 46, W09525,