Groundwater in a Changing Climate

By NAOMI LUBICK

Environmental Science and Technology, September 12, 2007

Climate change will not only affect the atmosphere and global average temperature; it will influence groundwater in both the near and deep subsurface, stresses a suite of research papers published online August 23 in the Vadose Zone Journal.

Both human infrastructure and climate change will affect the way water moves below ground.

Changing rainfall patterns are expected to influence the amount of water available in soils and change groundwater patterns. Shifts in vegetation and soil types in Mediterranean-like climes that are caused by a doubling of atmospheric CO2 will also alter groundwater recharge rates, according to climate models for Australia-which is already experiencing intense drought-and elsewhere. When rainfall increased in the models, recharge rates tended to rise. But the increases were highly dependent on vegetation types and varied from region to region, authors from the U.S. Department of Agriculture and Australia's Commonwealth Scientific and Industrial Research Organisation conclude.

Pumping groundwater in a changing climate -- on low-lying islands and atolls as well as from the High Plains aquifer in the central U.S.  -- also could have undesired effects. Researchers project an increased movement of toxins, including E. coli from fecal material, leaching into groundwater -- as, for example, on the island of Bonriki in the Pacific. Other researchers note that the High Plains aquifer is "potentially vulnerable" to the movement of Cl- and NO3- with changes in rainfall.

Heat islands from major cities will grow as climate changes, altering the temperature gradient underground. The longer the warming above, the deeper and greater the increase in warming below. This geothermal alteration could in turn affect the geochemistry and microbiology of groundwater -- a particular concern for Asian cities experiencing rapid population growth, researchers note.

Other papers in the suite examine the impact of climate change on nitrate leaching, surface stream flows with regional groundwater shifts, and sand dams used to store water in Kenya. Despite increased precipitation, climate projections show an increase in evaporation with higher global temperatures, and the changes in water demand and dams underscore the interactions of human activities with climate changes.

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