INTEGRATING KNOWLEDGE OF COLD AIR POOLING DYNAMICS INTO
CLIMATE CHANGE ADAPTATION STRATEGIES
Authors:
a
Buhler ,
M. J., D. M.
a
Dulen ,
D.
b
Cayan ,
M.
c
Tyree ,
C. S.
a
Fong
and A.L.T.
a
Osborne
a: NPS Devils Postpile National Monument, Mammoth Lakes, CA; b: Scripts Institute of Oceanography, La Jolla, CA; c: UCSD, San Diego, CA
INTRODUCTION
METHODS (cont.)
We present preliminary results of a five year study of the physical
dynamics of cold air pooling and consideration of the potential role
of cold air pools (CAPs) in maintaining climate change refugia in Devils
Postpile National Monument (DEPO). CAPs are temperature inversions
that occur in confined terrain where cold, dense air becomes trapped
and concentrated, resulting in cooler and moister conditions as
compared to the surrounding, often higher elevation, area.
Preliminary results of the study indicate that CAP formation is
influenced by time of day, season, weather patterns, and possibly
influenced by climatic conditions such as drought. CAPs influence on
the physical environment play an important role in maintaining
refugia characteristics, such as wet meadows and riparian habitats,
however, the effects of climate change on the CAP process are
unknown and a better understanding of CAP dynamics is essential to
predict whether this process will continue to provide cooler and
moister conditions or if CAP events will decrease in frequency or stop
occurring altogether. This knowledge is vital for the development of
effective climate change adaptation strategies that focus on refugia
at DEPO for conservation and resource management.
BACKGROUND
DEPO is located in the Central Sierra Nevada of California (Figure 1).
Based on an algorithm for predicting CAPs, Lundquist et al. (2008)
determined that areas of DEPO exhibited characteristics of a CAP. To
increase our understanding of the DEPO CAP, Scripps Institution of
Oceanography (SIO)-University of California at San Diego (UCSD),
United States Geological Survey (USGS), and DEPO developed a study
to verify areas of DEPO that constitute a CAP and characterize the
magnitude, duration, season, frequency, and rate of change of CAP
events.
CAP days Total days
Year in Aug.
in Aug.
2009
11
31
2010
24
31
2011
13
31
2012
5
31
2013
6
14*
Figure 5: iButton in radiation shield.
Figure 4: Temperature logger installation.
Figure 6: Logger placement within the
tree canopy for optimal shading.
Figure 7: Distribution of temperature loggers in
and around Devils Postpile.
RESULTS
For the initial analysis, we chose five sites (Figure 8) that have the longest record of temperature data (20092013). During August (Figure 9), low elevation sites (e.g. 30.01 and 21.01) are consistently cooler than higher
elevation sites (e.g. 17.01) from 10:00pm when CAP development begins and 6:00am when the CAP breaks up.
As expected, daytime temperatures at lower elevation sites show warmer temperatures than higher sites. The
greatest temperature gradient between elevations occurs in the night and early morning hours.
Figure 9: August average
diurnal temperature cycle
between 2009 and 2013 for
five sites with the CAP logger
distribution.
The average temperature difference at 6am in August due to CAP is 6°C between
sites 17.01 and 30.01. Using this difference as the threshold to designate a CAP
event, we calculated the number of CAP days occurring from 2009 – 2013 (Figure
10). Cold air pooling tends to occur more often during the warmer part of the year;
from July through September. CAP frequency decreases during the winter months in
part due to changing meteorological patterns.
Figure 2: Rainbow Falls (above)
Figure 3: Soda Springs Meadow (below)
METHODS
Since 2008, we have placed over one hundred temperature sensors
(Hobo tidbits and iButtons) along east-west transects in and around
DEPO to record temperature data along an elevational gradient. The
loggers are located in live trees, singularly or at different heights (e.g.
1m, 5m, 10m, 20m, 30m) in a single tree to determine both coarse
and fine scale temperature variation. Temperature is recorded every
30, 60, or 120 minutes depending on location, and data are
downloaded on an annual or biannual basis. Over time, the number
and distribution of temperature sensors has increased to refine
documentation of the complexity of the DEPO CAP.
Table 1: Frequency of CAP days
during the month of August from
2009 to 2013. *data are not available
for the remaining 15 days
Figure 11: Snow water equivalent in inches for water years
2009/2010 (wet) and 2013/2014 (dry)
Figure 8: Distribution of
temperature loggers used in
current study analyses.
Figure 1: Location of Devils Postpile within
the Sierra Nevada range.
RESULTS (continued)
Figure 10: Percent of days per month showing a CAP event as defined by a difference of 6°
C between sites 17.01 and 30.01 (230 m difference in elevation). X’s indicate missing data
CAP frequency tends to occur over
several days, typically during multi-day
large scale meteorological patterns such
as high pressure systems seated over
the region, which feature clear skies,
low winds, low humidity, and relatively
high daytime temperatures. This
promotes radiative (infrared) nighttime
cooling, and a stable, layered
atmosphere near the ground with little
mixing, allowing cool nighttime
temperatures to collect in low elevation
valleys and pockets.
Between 2009-2013, two of the driest and one of the wettest winters (2010/2011 - not
shown due to missing data) on record for the Sierra Nevada occurred. The winter of
2012/2013 measured 20% of normal precipitation while the winter of 2009/2010
measured 120% of normal precipitation by April 1st (Figure 11). As shown in Figure 10
and Table 1, the frequency of CAP development in the summer months is much higher
in the wetter years (e.g. 2009/2010 and 2010/2011) as compared to drought years such
as 2012/2013 and 2013/2014. CAPs developed every day in July of 2010.
DISCUSSION & MANAGEMENT IMPLICATIONS
Results indicate that CAP formation is determined primarily by time of day, season, and
weather patterns and possibly influenced by longer term climate conditions such as
drought. Climate change predictions for the Sierra Nevada anticipate warmer
temperatures, less precipitation, and less snowpack. Although many factors may
contribute to CAP formation, results indicate that during drought years and less
snowpack CAP frequency decreased. For example, CAP developed on 24 days in August
2010 as compared to only 5 days in 2012. July and August are typically the warmest
months and decreased nocturnal cooling may reduce water availability and stress
wetland and riparian plants. However, some cooling may still occur and be sufficient to
support this habitat when compared to non-CAP sites. Additional analysis of these
results to determine other impacts on temperature, such as canopy cover, position in
the canopy, shading, and proximity to the river and riparian areas, may clarify the
variation in CAP frequency between years. To predict future CAP conditions, main
drivers of CAP formation patterns should be isolated, such as specific atmospheric
conditions and/or snowpack levels.
Preliminary analyses of these data along with identifying ecological components in
DEPO indicate that this area may provide climate refugia. While the CAP process itself
does not constitute refugia, the conditions that it provides (e.g., cooler and moister
habitats) maintain important refugia components such as wet meadows and riparian
habitats. Here we define climate change refugia as areas that are buffered from
climate change effects so as to favor greater persistence of physical and ecological
resources relative to other areas. Improved understanding of the potential impacts of
climate change on the CAP process and refugia components can guide the development
of climate adaptation strategies.
CONCLUSION
Thus far, results do not indicate that the CAP near DEPO is unique but is an important
physical component of refugia that is present in other mountainous regions. Additional
analysis and Information on CAP dynamics is essential for predicting whether the
effects of climate change will compromise refugial conditions (e.g. moister and cooler)
and if the CAP process will buffer climate change effects and provide refugia for in situ
species as well as species with compromised native habitats. Future climate change
adaptation strategies and management at DEPO will utilize this study to understand and
maximize refugia potential and protection in the park.
ACKNOWLEDGEMENTS
Scripps Institute of Oceanography, United States Geological Survey, National Park
Service, Student Conservation Association, Inyo National Forest and University of
California at San Diego