Conservation Ecology: Linkages between water vapor flows, food production and terrestrial ecosystem services: Appendix 3

Appendix 3. Estimating evaporating surface runoff from croplands.

The amount of water available for redirection from evaporating surface runoff in semiarid and arid regions for use in croplands is hard to estimate. We assumed that the difference in surface runoff coefficients between field scale and continental scale for croplands in Africa, Asia, and South America is attributed to evaporating surface runoff. An even distribution of croplands on the different continents was assumed. Croplands cover 10.5% of the global terrestrial area.

Continent	Precipitation^a	Surface runoff^a	Runoff coefficient, continental scale	Runoff coefficient, field scale	Difference in surface runoff	Evaporating surface runoff (10.5% croplands^b)
Continent	km³/yr	km³/yr	%	%	km³/yr	km³/yr
Africa	20780	2480	12	20	1676	176
Asia	32140	9130	28	30	512	54
South America	29355	6450	22	25	889	94
Sum						324

^a Data from L´vovich and White (1990).
b The global cropland area is roughly 10.5% of the global terrestrial area.