Decision support experiments and evaluations using seasonal to ...

The U.S. Climate Change Science Program Chapter 3
Emerging energy
sources, such as
biofuels, synfuels,
and hydrogen,
will add to future
water demands.
82
climate change and variability because it is subject
to highly variable rates of recharge and has
undergone a steady increase in pumping rates
over the last century. While groundwater overdraft
is most common in the arid and semi-arid
western United States (Roy et al., 2005; Hurd
et al., 1999), it is not uncommon in the more
humid East. Lyon et al. (2005) study the causes
of the three drought emergencies that have been
declared in Rockland County, New York since
1995. Seventy-eight percent of the county’s
public water supply is from small regional
aquifers. Rather than increased frequency or
intensity of meteorologic or hydrologic drought,
the authors attribute drought emergencies to
development and population growth overtaxing
local supplies and to failure of aging watersupply
infrastructure. The former is an example
of demand-driven drought. The Ipswich River
Basin in northeast Massachusetts is another
example in the East where population growth is
taxing groundwater resources. Because of reliance
on ground water and in-stream flows for
municipal and industrial supply, summer low
flows in the Ipswich frequently reach critical
levels (Zarriello and Ries, 2000).
A few researchers have studied the potential application
of SI climate forecasting to forecasting
of groundwater recharge and its implications
for water management. For example, using
U.S. Geological Survey recharge estimates for
the Edwards Aquifer from 1970 to 1996, Chen
et al. (2005) find that recharge rates during La
Niña years average about twice those during
El Niño years. Using a stochastic dynamic programming
model, they show that optimal water
use and allocation decision making based on El
Niño-Southern Oscillation (ENSO) 10 forecasts
could result in benefits of $1.1 to $3.5 million
per year, mainly to agricultural users as a result
of cropping decisions.
10 The Southern Oscillation Index (SOI) is a calculation
of monthly or seasonal fluctuations in the air pressure
difference between Tahiti and Darwin, Australia.
When the air pressure in Tahiti is below normal and
the air pressure in Darwin is above normal, the SOI
is in a negative phase. Prolonged periods of negative
SOI values often occur with abnormally warm ocean
waters across the eastern tropical Pacific resulting in a
period called an El Niño. Conversely, prolonged periods
of positive SOI values (air pressure in Tahiti is above
normal and in Darwin it is below normal) coincides
with abnormally cold ocean waters across the eastern
tropical Pacific and is called a La Niña.
Hanson and Dettinger (2005) evaluate the SI
predictability of groundwater levels in the Santa
Clara-Calleguas Basin in coastal Southern
California using a regional groundwater model
(RGWM) as driven by a general circulation
model (GCM). In agreement with other studies,
they find a strong association between
groundwater levels and the Pacific Decadal
Oscillation (PDO) and ENSO. Their results led
them to conclude that coupled GCM-RGWM
modeling is useful for planning and management
purposes, particularly with regard to
conjunctive use of surface and ground water and
the prevention of saltwater intrusion. They also
suggest that GCM forecast skill may at times
be strong enough to predict groundwater levels.
Forecasts of greater surface water availability
may allow utilities to reduce reliance on overutilized
and expensive groundwater resources.
Bales et al. (2004) note that a forecast for heavy
winter snowpack during the 1997/1998 El Niño
led the Salt River Project in Arizona to reducing
groundwater pumping in the fall and winter
in favor of greater releases from reservoirs,
thereby saving about $1 million.
Water Supply and Energy Production:
Adequate water supplies are an essential part
of energy production, from energy resource
extraction (mining) to electric-power generation
(DOE, 2006). Water withdrawals for cooling
and scrubbing in thermoelectric generation
now exceed those for agriculture in the United
States (Hutson et al., 2004), and this difference
becomes much greater when hydropower uses
are considered. Emerging energy sources, such
as biofuels, synfuels, and hydrogen, will add to
future water demands. Another new energyrelated
stress on water resource systems will
be the integration of hydropower with other
intermittent renewables, such as wind and solar,
at the power system level. Hydropower is a very
flexible, low-cost generating source that can be
used to balance periods when other renewables
are not available (e.g., times of calm winds)
and thus maintain electricity transmission
reliability. As more non-hydro renewables are
added to transmission grids, calls for fluctuating
hydropower operation may become more
frequent and economically valuable, and may
compete with other water demands. If electricity
demand increases by 50 percent in the next