26 April 2009

Global Groundwater Recharge Map & Water Use

Ever wondered how much water percolates into the ground? Petra Doell et al., a few years back, published a global map of estimated groundwater recharge, which they recently updated and extensively discussed in a public journal article that includes beautiful color maps (I admit - I always liked looking at good maps). An interactive version of the recharge map is available now at the WHYMAP (world-wide hydrogeological assessment and mapping program).

Global groundwater recharge is nearly 13 thousand cubic kilometers (a little more than 10 thousand million acre-feet) or about one-third of all renewable water resources. On average that is a little over 2000 cubic meters of renewable groundwater per capita per year, but may be as little as 10 cubic meters in some arid countries (for comparison: FAO estimates that at least 1700 cubic meters of water are needed annually per capita to meet living standards). Not surprisingly, the least available recharge or renewable groundwater (per capita) is in arid and semi-arid regions - much of China, India, Pakistan, Middle East, Northern Africa, and the U.S. Southwest/Mexico. Notably - these are also regions, where much of the global groundwater extraction occurs (because renewable surface water resources are equally scarce there).

Speaking of groundwater extraction: The reason I stumbled across this today is a wonderful book called "The Agricultural Groundwater Revolution" edited by Mark Giordano and Karen Villholth. It provides a comprehensive overview of groundwater use, management, and policy in agricultural regions around the world. I can highly recommend the reading! Among many other things, the book provides an insight into groundwater pumping in many regions.

I needed to familiarize myself with some of these numbers and how they stack up against those that I know (for example, the California water budget). Here are some big numbers I came up with that may serve otheres as comparison as well (I apologize for the poor table format. Sources I used: USGS Circular 1298 for California and the U.S., Pacific Institute's World Water Report for world total, which lumps domestic and public water supply into a single category):

Note: GW refers to groundwater, SW refers to surface water; "industrial" also includes water use in mining and energy production. The above numbers are freshwater supplies only.

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