It’s no simple matter to figure out how regional changes in precipitation, expected to result from global climate change, may affect water supplies. Now, a new analysis led by MIT researchers has found that the changes in groundwater may actually be much greater than the precipitation changes themselves.
For example, in places where annual rainfall may increase by 20% as a result of climate change, the groundwater might increase as much as 40%. Conversely, the analysis showed in some cases just a 20% decrease in rainfall could lead to a 70% decrease in the recharging of local aquifers—a potentially devastating blow in semi-arid and arid regions.
But the exact effects depend on a complex mix of factors, including soil type, vegetation, and the exact timing and duration of rainfall events, so detailed studies will be required for each local region in order to predict the possible range of outcomes.
The research was conducted by Gene-Hua Crystal Ng, now a post-doctoral researcher in MIT’s Department of Civil and Environmental Engineering (CEE), along with King Bhumibol Professor Dennis McLaughlin and Bacardi Stockholm Water Foundations Professor Dara Entekhabi, both of CEE, and Bridget Scanlon, a senior researcher at the University of Texas.
The analysis combines computer modeling and natural chloride tracer data to determine how precipitation, soil properties, and vegetation affect the transport of water from the surface to the aquifers below. This analysis focused on a specific semi-arid region near Lubbock, Texas, in the southern High Plains.
Predictions of the kinds and magnitudes of precipitation changes that may occur as the planet warms are included in the reports by the Intergovernmental Panel on Climate Change (IPCC)and are expressed as ranges of possible outcomes. “Because there is so much uncertainty, we wanted to be able to bracket the expected impact on water supplies under the diverse climate projections,” Ng says.
“What we found was very interesting,” Ng continues. “It looks like the changes in recharge could be even greater than the changes in climate. For a given percentage change in precipitation, we’re getting even greater changes in recharge rates.”
The team presented the results as a range of probabilities, quantifying as much as possible “what we do and don’t know” about the future climate and land-surface conditions, Ng says. “For each prediction of climate change, we get a distribution of possible recharge values.”
For more study results, go to http://web.mit.edu/newsoffice/2008/agu-groundwater-1218.html.
Read more about civil engineering and climate change at www.GraduatingEngineer.com.