Development of a GIS Database to Evaluate Climate-Induced Streamflow Timing Changes
in California
Daniel J. Bates1, Iris T. Stewart-Frey2 and Edwin P. Maurer3
1Santa
Poster GC-21A-0701
Clara University, Santa Clara, CA (DBates@scu.edu) 2Santa Clara University, Environmental Studies Institute, Santa Clara, CA (IStewartFrey@scu.edu) 3Santa Clara
University, Department of Civil Engineering, Santa Clara, CA (EMaurer@scu.edu)
Introduction
Recent Studies have indicated that an increase in average
temperatures has led to reduced snowpack and earlier timing of the
spring pulse throughout California and the West (i.e, Mote et al., 2005;
Hamlet et al., 2007; Regonda et al., 2005; Stewart et al., 2005). This
correlation between climate change and snowmelt timing is expected
to have serious implications and impacts on ecosystems and water
resources.
While the link between increased temperature and earlier
snowmelt and snowmelt runoff is well supported and seems logical
from physical principles, a very wide range of streamflow responses to
climate change exist that have not yet been understood. Our hypothesis
is, that, while differences in climatic influences contribute, the
combination of physical characteristics of a watershed (i.e. elevation
distribution, ground cover, slope, soil thickness, aspect, latitude etc.)
significantly contribute to an individual basin’s response. In order to
better predict streamflow and plan for water resources management of
California’s reservoir network it is imperative to understand the
interaction of watershed characteristics and streamflow response
accurately. The overall goals of this study then, are to
• Delineate and characterize the physical characteristics of snowmelt
dominated streams to explain the differences in watershed response to
climatic changes through a statistical analysis, and
•Use the insights and characterizations gained in the initial steps for
physially-based modeling.
This poster describes the methods and results of the watershed
characterization using GIS, the first part of our study.
Methods Watershed Delineation continued
Stream location data was obtained from the USGS National Hydrography
Dataset (NHD; http://nhd.usgs.gov). The delineation process was executed
with the following steps in ArcHydro:
-DEM Reconditioning
-Fill Sinks
-Flow Direction
-Flow Accumulation
-Stream Definition
-Stream Segmentation
-Catchment Grid Delineation
-Catchment polygon Processing
-Drainage Line processing
-Adjoint Catchment Processing
-Batch Watershed Delineation
Elevation Bands
Elevation in the clipped watersheds ranged from 0 to 6000 m. Using 250 m
intervals and the ArcPython scripting capacity, the amount of area in each 250
m elevation band was determined
Figure 3. Gauge
11264500
Watershed on the
Merced River at
Happy Isles. a)
Base layer b)
Elevation bands
1000
Figure 3. Ground cover type distribution.
CON=conifer forest/woodland;
HDW=hardwood forest/woodland
MIX=mixed conifer/hardwood woodland
SHB=shrub; HEB=herbaceous
BAR=barren, rock, snow; WAT=water
AGR=agriculture; URB=urban/residential
NYM=not yet mapped
Figure 4. Close-up
on gauge
11264500
watershed
vegetation
distribution (same
symbology as
Figure 3).
Analysis
Watershed size, elevation
distribution, and ground cover
distribution was compiled and
analyzed for all watersheds (see
Figure 5)
2000
3000
4000
5000
Elevation (m)
Figure 3. a) Elevation distribution for all gauges taken together b) The
number of watersheds in each size class.
Conclusions
The watershed delineation and characterization process are
describing mountainous environments that are comparatively free of
human influences and have been affected by warmer temperatures
over the past several decades. It is important to note that a large
fraction of these climate-change-affected watersheds are at higher
elevations (>2000 m) than those recognized as most vulnerable (i.e.
Hamlet et al., 2007). Relating watershed characteristics to streamflow
timing changes will allow for a better understanding of climate
changes impact on human resources, and provide data for future
resource management of California’s water supplies.
Literature cited
Hamlet AF, Mote PW, Clark MP, Lettenmaier DP 2007. Twentieth-century trends in runoff,
evapotranspiration, and soil moisture in the western United States. Journal of Climate 20:1468 –
1486. doi: 10.1175/JCLI4051.1
Mote PW, Hamlet AF, Clark MP, Lettenmaier DP. 2005. Declining mountain snowpack in western North
America. Bulletin of the American Meteorological Society 86(1):39-49. doi: 10.1175/BAMS-86-139
Regonda SK, Rajagopalan B, Clark M, Pitlick J. 2005. Seasonal cycle shifts in hydroclimatology over the
western United States. Journal of Climate 18(2):372-84.
ides/dem.html. Cell
size= 30 m) were
obtained for the
relevant regions,
primarily in the
Sierra Nevadas and
mosaiced together.
Figure 1. California
streamflow gauges on top
of the mosaiced DEM for
the study region
b)
Vegetation Bands
Vegetation data was obtained from California’s Fire and Resources
Assessment Program (FRAP) for each county in California and mosaiced
together for watershed clipping (Figure 3).
Approximately 50 California streamflow gauges were identified to be
relatively unaffected by human influences, snowmelt dominated and
have at least 20 years of continuous data. For the watersheds
associated with these gauges, we used GIS to delineate and
characterize:
• The watershed boundary above the gauge, including watershed size
• Elevation distribution in 250 m elevation bands
• The relative percentage of ground cover type
Digital elevation
models
(http://edc.usgs.gov/gu
The delineation process described here allowed for the
identification of only that key region of a mountainous watershed that
is influencing a particular snowmelt dominated gauge. Watershed size
for the snowmelt-dominated gauges generally ranges from less than
100 to 1000 km2, in addition, there are three watersheds larger than
2000 km2. Taken together, the elevation of the majority of the study
area is approximately in the 1800-3000 meters elevation range, and the
most common types of ground cover in the delineated watersheds are
hardwood forest/woodland, conifer forest/woodland, and barren land.
The watershed delineations described here can now be related to
streamflow timing changes (see poster GC-21A-0700) and used in
further analysis.
a)
Methods
Watershed
Delineation
Results
Methods
Stewart IT, Cayan DR, Dettinger MD, 2005. Changes towards earlier streamflow timing across western
North America. Journal of Climate18:1136-1155
Figure 5. DEM of study
area with the delineated
snowmelt dominated
watersheds displayed.
Acknowledgments
Funding for the first author through Santa Clara
University internal grants is gratefully acknowledged.
The second author thanks the Clare Booth Luce
Foundation for its financial support.