Impacts of Population Growth, Climate Change, and

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					Impacts of Population Growth, Climate Change, and Land Use
  Change on Water Availability and Demand across North
        Carolina and the Southeastern US: Methods
           Ge Sun, Steven G. McNulty, Erica Cohen, and Jennifer Moore Myers

   Research Hydrologist, Research Ecologist and Project Leader, and Resource Information
  Specialists, respectively. Southern Global Change Program, USDA Forest Service, 920 Main
    Campus Dr. Venture II, Suite 300, Raleigh, NC 27606. Email: Tel
                                  9195159498. Fax 9195132978

Population, land use and land covers, and climate variability are expected to undergo dramatic
changes during the 21st century across the southern U.S. Water use and water availability for
both humans and ecosystems needs could be negatively altered to these changes across the
region. The objective of this study is to develop a method to fully budget annual water availability
(Preciptation-Evapotranspiration + Groundwater supply+Return Flow) and the regional water use
from major water-users (e.g. domestic, irrigation, industry). For natural water use, we used a
generalized annual actual evapotranspiration (AET) model that estimates water loss as a
function of potential ET, annual precipitation, landcover type, topography. The model was first
calibrated with a watershed-scale database derived from 39 forest-dominated watersheds
representing the diverse eco-regions of the Southeast. Then, the model was validated at a half a
degree spatial resolution across the region using historic hydrology, climate, and land cover
data. Gridded GIS databases for human-induced water use at the county level were developed
from published USGS data. Once the methods were developed, we applied the simulation
system to all 8 digit USGS Hydrologic Unit Code HUCs within 13 southern states with nine
hypothetical scenarios to examine the water resource impacts of population growth, landuse/land
cover changes, and climate change at a regional scale for the next 20 years. We proposed a
water shortage index as the ratio of water demand and water supply. The modeling system
accounts water supply and demand at an annual basis. This paper will present the research
methods and databases only, and results and implication will be discussed in a sequent paper at
the conference (McNulty et al.).