Will there be another Dust Bowl in the Great Plains similar to the one that swept the region in the 1930s? It depends on water storage underground. Ground water depth has a significant effect on whether the Great Plains will have a drought or bountiful year.
Recent modeling results show
that the depth of the water table, which results from lateral water flow at the
surface and subsurface, determines the relative susceptibility of regions to
changes in temperature and precipitation.
"Ground water is
critical to understand the processes of recharge and drought in a changing
climate," says Reed Maxwell, an atmospheric scientist at Lawrence
Livermore National Laboratory, who along with a colleague at Bonn University
analyzed the models that appear in a recent edition of the journal Nature
Maxwell and Stefan Kollet
studied the response of a watershed in the southern Great Plains in Oklahoma
using a ground-water/surface-water/land-surface model.
The southern Great Plains are
an important agricultural region that has experienced severe droughts during
the past century, including the dust bowl of the 1930s. This area is
characterized by little winter snowpack, rolling terrain and seasonal
While the onset of droughts in the region may depend on
sea surface temperature, the length and depth of major droughts appear to depend
on soil moisture conditions and land-atmosphere interactions.
That's what the recent study
takes into account. Maxwell and Kollet created three future climate simulations
based on the observed meteorological conditions from 1999. All included an increase
in air temperature of 36.5 degrees Fahrenheit. One had no change in
precipitation; one had an increase in precipitation by 20 percent; and one had
a decrease in precipitation by 20 percent.
"These disturbances were
meant to represent the variability and uncertainty in regional changes to
central North America under global model simulations of future climate,"
The models showed that ground
water storage acts as a moderator of watershed response and climate feedbacks. In
areas with a shallow water table, changes in land conditions, such as how wet
or dry the soil is and how much water is available for plant function, are
related to an increase in atmospheric temperatures. In areas with deep water
tables, changes at the land surface are directly related to amount of
precipitation and plant type.
But in the critical zone,
identified here between 6.5 feet and 16 feet deep, there is a very strong
correlation between the water table depth and the land surface.
"These findings also
have strong implications for drought and show a strong dependence on areas of
convergent flow and water table depth," Maxwell reveals. "The role of
lateral subsurface flow should not be ignored in climate-change simulations and
Water Table Depth Tied to Droughts
November 3, 2008