1. Water Resources Chapter Overview
Dennis P. Lettenmaier
Department of Civil and Environmental Engineering
University of Washington
for presentation at
SAP 4.3 Stakeholder Workshop
Baltimore
February 16, 2007

2. Runoff
Mean annual runoff, runoff ratio, and fraction of runoff originating as snow across the continental U.S. and Alaska
Runoff
ratio
Fraction from snow

3. Number of trends
Observed streamflow trends, (from Lins and Slack, GRL, 1999)
Location of trends

4. Changes in spring snowmelt runoff timing, western U.S., 1948-2000
Source: Stewart et al, J Clim, 2005

5. Projected changes in annual runoff, 2041-2060 relative to 1900-1970, from 24 GCMs run for IPCC 2006
Source: Milly et al, Nature 2005

6. Median runoff changes, 2041-2060 relative to 1900-1970, from 12 GCMs archived for IPCC 2006
Median changes by USGS water resources region
Number of model pairs (of 24) with increases minus decreases
Source: replotted from Milly et al, Nature, Visual courtesy Chris Milly, USGS

7. Chapter outline
Background – importance of water, current status of U.S. water resources
Observed changes in U.S. water resources, 20th Century.
Attribution of changes to a) climate change, b) land use/land cover, and c) other change agents
Future changes and impacts, based on refereed literature using GCM model runs archived for IPCC AR4
Implications for landscape – hydrology interactions – drought, fire, hydrology-vegetation feedbacks
Observing system – what do we have now, is it doing the job, how could it be improved?
Findings and conclusions