**Evaluating Key Uncertainties in IPCC Climate Change Projections of
California Snowpack: Topography, Snow Physics, and Aerosol Deposition**

Director's Research and Development Fund (DRDF)

\[\] Interim or \[x\] Final Report

JPL Task \# 1201

Duane Waliser, 3246, Water & Carbon Cycles, Sciences Division

Qinbin Li, 3247, Lab Studies and Modeling, Science Division

Annmarie Eldering, 3283, Tropospheric Emission Spectrometer, Science
Division

Yi Chao, 3248, Ocean-Atmos. Interaction, Science Division

Saasan Saatchi, 334H

Kuo-Nan Liou, Department of Atmospheric and Oceanic Sciences (AOS), UCLA

Yongkang Xue, Department of Geography, UCLA

Jinwon Kim, Department of AOS, UCLA

Alex Hall, Department of AOS, UCLA

Robert Fovell, Department of AOS, UCLA

# A. OBJECTIVES 

There are three objectives of this activity. Objective one aims at
investigating the impact of model resolutions on projecting the climate
change impact on the Sierra snowpack. Objective two explores the impact
of snow albedo changes on the simulation and projection of the Sierra
snowpack, respectively. Objective three examines how a more
comprehensive parameterization of snow process, specifically an advanced
multi-layer treatment of snow cover relative to a single-layer model,
influences the loss rate of snowpack.

# B. APPROACH AND RESULTS 

(Objective I) In order to investigate the impact of model resolution on
projecting the climate change impact on the Sierra snowpack, we compared
the climate change signals in snow-water equivalence in California
projected by a GCM, the NCAR CCSM3, and the WRF model driven by the
large-scale forcing obtained by the same GCM scenario. The benefit of
dynamical downscaling is immediately clear in Figure 1, which compares
the climate change signals in snow-water equivalent (SWE) in the 36km
resolution regional climate simulation and the NCAR CCSM3 used to drive
the regional run. The climate change signals in Figure 1 are presented
in terms of the percentage differences in SWE between the future and
present-day climate. In the dynamically downscaled projection (Fig. 1a),
the largest changes in SWE occurs over the high elevation regions in the
Sierra Nevada, Mt. Shasta, and the Cascades. The GCM projection
generated similar magnitude in the largest climate change impact on SWE
as in the downscaled simulation; however, the SWE change signals occur
mostly in northern California and the southern Oregon region. These
differences between the GCM and the downscaled projections occur
primarily due to the model terrain representations in the two models of
different spatial resolution. Additional analysis has been undertaken in
comparing the 36km resolution domain and that simulated by a (one-way)
nested 12km domain (not shown -- see Waliser et al. 2008).

(Objective II) The impact of aerosol deposition on the snow albedo and
the subsequent evolution of the Sierra snowpack have been investigated
in a sensitivity study in which five winter-season simulations have been
performed with 5 different snow albedo fields. In the control
simulation, the default values of snow albedo provided with the WRF
model were used. In the remaining four sensitivity runs, the default
values were modified to be 75, 90, 110, and 125% of the control run. The
two smaller snow albedo values represent the cases in which black carbon
emissions in California will continue to increase in the future. The two
larger snow albedo values assume the cases in which anthropogenic
emissions will be reduced by successful implementation of recent
mandates by California\'s governor. This investigation is qualitative
because of the amount of aerosol deposits and the quantitative
relationship between aerosol deposition and snow albedo has not been
well established at this time. The simulations were performed over a
12km-resolution California domain (Figure 2). The largest sensitivity of
the Sierra snowpack to snow albedo changes occurs in high elevation
regions during late winter and early spring (Figure 3). In the lowest
two elevation ranges, 1750-2000m and 2000-2250m, reduction of snow
albedo by 25% resulted in the reduction in SWE by as much as 20% of the
control run (Figures 3a,b). Increases in snow albedo generate similar
sensitivity in SWE of an opposite sign. Notable response to snow albedo
in these two low elevation regions occurs in the mid part of the cold
season. The sensitivity of snowpack amounts to the changes in the snow
albedo increase becomes larger in higher elevation. In higher elevation,
the period of largest sensitivity occurs later in the season compared to
lower elevations. In the lowest two elevations, the maximum reduction in
SWE associated with smaller snow albedo occurs in December (Figures
3a,b). In the two mid-elevation regions (Figures 3c,d), the maximum SWE
sensitivity with the snow albedo of 75% of the control run occurs in
January. In the highest two elevation, the peak response to SWE to the
reduced snow albedo occurs in February. Similarly, the timing for peak
increase in SWE due to increased snow albedo occurs later in the season
as the terrain elevation increases. Additional results can be found in
Waliser et al. (2008).

(Objective III) In order to compare the results of a more sophisticated
three-layer snow model to the simpler single-layer version, it was
necessary to update the vegetation map within WRF that was based on USGS
to the one used by SSiB. The SSiB map includes both USGS and University
of Maryland global vegetation maps, which include most up-to-date
information. In addition, it was necessary to implement a sea-ice code
into WRF so that long-term integrations could be performed; the original
WRF fixes the sea ice. Figure 4 shows the results of a comparison
between the three-layer version and the single-layer version in terms of
SWE field for May 1998. In this case, boundary conditions were supplied
by the NCEP/NCAR reanalysis. Results in this study show that the
simulation with the multi-layer snow model reduce the SWE biases in the
single-layer snow model simulation by significant amounts, especially in
the eastern and central Canadian regions and the high biases in the
western US. These results indicate that use of more sophisticated
mulit-layer treatments may lead to more rapid snowpack loss under global
warming conditions projected such as in the IPCC assessments. Additional
results can be found in Waliser et al. (2008).

# C. SIGNIFICANCE OF RESULTS 

Progress to date has resulted in the application of the new
state-of-the-art regional Earth System model that was developed in the
previous year via DRDF support. The results support the notion that
significant uncertainties exist in projections of snowpack by GCM-class
models utilized in the IPCC assessments (e.g., Assessment Report 4).
These include the possible overestimate of snowpack loss due to course
resolution, uncertainty due to uknowns associated with carbon and other
aerosol emissions and their influence on snow albedo, and the likely
underestimate of snowpack loss due to typical use of single-layer
models. By completing this work, we are in an advantageous position to
build on this modeling work and attract additional funding in the
climate and mission design context. In particular, this work has helped
form the basis for three scientific contributions to the 2008 California
Environmental Protection Agency (CalEPA) / California Energy Commission
(CEC) biennial science report on the potential impact of continued
global warming on a number of California's environmental assets and
economics sectors. These three reports will also be submitted to the
corresponding peer-reviewed special journal issue to be determined.
These three reports are listed in the Publication section and noted with
asterisks.

# D.      NEW TECHNOLOGY 

None.

# E. FINANCIAL STATUS 

No funding remains.

# F.      ACKNOWLEDGEMENTS 

We wish to express thanks to the Chief Scientist and Technologist Office
for their support of this work.

# G. PUBLICATIONS 

-   D. Waliser, Y. Chao, [A. Eldering]{.underline}, R. Fovell, R.
    Friedl, [A. Hall]{.underline}, J. Kim, Q. Li, K.N. Liou, J.
    McWilliams, Y. Xue. 2007. Modeling and Observing the Earth System on
    Regional Scales: A Joint UCLA-JPL Research Effort Focused on Climate
    Variability and Change In California, Fourth Annual Climate Change
    Research Conference, September 10 - 13, 2007 Sacramento Convention
    Center, Sacramento, CA.

-   Kim. J., D. Waliser, Q. Li, K. Liou, C. Cai, Y. Chao, A.
    Eldering, R. Fovell, A. Hall, X. Qu, and Y. Xue, 2007: The JIFRESSE
    Regional Earth System Model and its application to air quality in
    California. AGU Fall meeting, GC21A-0137, December 11, 2007, San
    Francisco, California, American Geophysical Union.

-   Eldering, A., A. Hall, J. Kim, R. Fovell, Y. Chao, Q. Li, K.-N.
    Liou, J. McWilliams, D. Waliser, and Y. Xu, 2008: A projection of
    climate change on the hydroclimate in California based on CCSM3 and
    JIFRESSE RESM: A joint UCLA-JPL research effort on modeling and
    observing the Earth system on regional scales. US CLIVAR
    Summit,14-16 July 2008, Irvine, California.

-   \*\*Kim, J., Y. Chao, A. Eldering, R. Fovell, A. Hall, Q. Li, K.
    Liou, J. McWilliams, D. Waliser, Y. Xue, and Sarah Kapnick, 2008: A
    projection of the cold season hydroclimate in California in mid-21st
    century under the SRES-A1B emission scenario, Fifth Annual Climate
    Change Research Conference, September 8-10, 2008, Sacramento
    Convention Center, Sacramento, CA.

-   \*\*Hughes M. Hughes, A. Hall, J. Kim, Anthropogenic Reduction of
    Santa Ana Winds, Fifth Annual Climate Change Research Conference,
    September 8-10, 2008, Sacramento Convention Center, Sacramento, CA.

-   D. Waliser, J. Kim, K. Liou, Y. Xue, A. Eldering, A. Hall, Y.
    Chao, R. Fovell, Q. Li, J. McWilliams 2008: Anthropogenic Climate
    Changes in California: Hydroclimate, Snowpack, and Santa Ana Winds,
    Fifth Annual Climate Change Research Conference, September 8-10,
    2008, Sacramento, CA.

-   •\*\* Waliser, D., J. Kim, Y. Xue, Chao, Y., A. Eldering, R.
    Fovell, A. Hall, Q. Li, K. Liou, J. McWilliams, S. Kapnick, R.
    Vasic, Fs. De Sale, and Y. Yu, 2008, Simulating the Sierra Nevada
    snowpack: The impact of snow albedo and multi-layer snow physics,
    Fifth Annual Climate Change Research Conference, September 8-10,
    2008, Sacramento, CA.

\*\* Also a contribution to the CEC's and CEPA's Biennial 2008
California Climate Change Report (in press), and expected peer-reviewed
submissions to an associated special issue of *Climatic Change*.

# H. REFERENCES 

Nonew

# J. FIGURES 

![](media/image1.png){width="3.8097222222222222in"
height="2.7069444444444444in"}

Figure 1. Percent differences in SWE between the two 20-year periods,
1961-1980 (late 20th century) and 2035-2054 (mid-21st century) obtained
in (a) dynamical downscaling of the NCAR CCSM projections at a 36km
resolution using the WRF model and (2) the corresponding CCSM3
projection.

![](media/image2.png){width="2.0395833333333333in"
height="2.4972222222222222in"}

Figure 2. The model terrain in the California domain represented at a
12km resolution.

![](media/image3.png){width="3.2694444444444444in"
height="3.0069444444444446in"}

Figure 3. The ratio of the SWE in the 4 sensitivity runs to that in the
control run within 6 elevation ranges (1750-2000m, 2000-2250m,
2250-2500m, 2750-3000m, and above 3000m). Note that the ordinate of
(c) - (f) is in a logarithmic scale.

![](media/image4.png){width="3.2395833333333335in"
height="5.059722222222222in"}

Figure 4. The biases in the simulated SWE for May 1998: (a) single-layer
snow model and (b) three-layer snow model.