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The models generally show a warm bias in summer for this
region but lower bias in winter. By contrast, precipitation
amounts simulated for winter are higher than observations,
and the annual maximum generally occurs about one month
earlier than is observed. The spring-to-summer decrease in
precipitation is more abrupt in the models than in
observations.
The delayed peak in seasonal precipitation in the models
leads to a delayed seasonal peak in streamflow as well, as
shown in Fig. 1c. The range of results for streamflow is
larger than the range in either temperature or precipitation.
For instance if a model is both too warm and too dry it has
two factors leading to a low simulations of streamflow.
All regional models capture two major features of the
interannual variability that occurred during the period of
1980-2004. The major flood of 1993 was the dominant
hydrological feature of this region over the period simulated.
Individual models have systematic biases over the entire
simulated record, but all capture the flood of 1993, albeit
with reduced or amplified (depending on bias) difference
from the long term mean. All models also capture the
weaker extreme dry period of 2000, although with less
distinctiveness than the flood year. Small interannual
variations are simulated differently by individual models,
with some showing much less variability, particularly in the
first half of the record.
5. Future Results
SWAT simulations with results of additional NARCCAP
models are in progress and will be reported at the workshop.
6. Acknowledgement
We acknowledge the North American Regional Climate
Change Assessment Program (NARCCAP) including the
climate modeling groups and the NCAR/LLNL archiving
teams (http://www.narccap.ucar.edu/about/participants.html)
for providing the data used in this publication. NARCCAP is
funded by the US National Science Foundation, US
Department of Energy, the National Oceanic and
Atmospheric Administration (NOAA) and the U. S.
Environmental Protection Agency Office of Research and
Development. Partial support for this work was provided by
USDA National Research Initiative Grant
#20063561516724.
References
NARCCAP, 2009: North American Regional Climate
Change Assessment Program. [Available online at
http://www.narccap.ucar.edu ]
Neitsch, S.L., J.G. Arnold, J.R. Kiniry, R. Srinivasan, and
J.R. Williams (2002), Soil and Water Assessment
Tool: User Manual, Version 2000, Texas Water
Resour. Inst. TR-192, GSWRL 02-02, BRC 02-06.
455 pp.