Friday, May 12, 2017

Climate Change and Skiing in the United States

Projections of how climate change will impact snow and skiing are of great interest to readers of this blog.  There are, however, a number of major challenges to making these projections.  Our climate models have large grid spacings, which means they do not explicitly simulate the effects of nearly all mountain barriers on precipitation, humidity, temperature, etc.  Without reasonable mountains, they don't explicitly simulate the mountain snowpack, or the effects of elevation and aspect on that snowpack.  Therefore, projecting how snow will change in the future typically requires some modeling gymnastics to account for local effects in mountainous regions.

A recent paper by Wobus et al. in Global Environmental Change uses a variety of approaches to project future climate change impacts on snow, skiing, and snowmobiling in the contiguous United States.  The paper is unique in that it doesn't focus on a particular ski area or region, but instead provides a nationwide perspective on climate change and skiing.

They use the Utah Energy Balance Model (UEB), developed at Utah State to simulate the water and energy balance of seasonal snowpacks, to simulate natural snow at each ski area or winter-recreation location (247 in total).  They drive the UEB with projections from five climate modeling systems (selected to provide a reasonable sample of climate change scenarios generated by the full spectrum of climate models), which are adjusted using a variety of approaches to account for the regional and local climatic effects on temperature, precipitation, and moisture conditions at each ski area and winter-recreation location.  They present changes in season lengths for cross-country skiing and snowmobiling sites, which one could think of as relevant for backcountry skiing, as well as alpine skiing resorts, which also attempt to account for snowmaking.  They do this for two scenarios, RCP4.5, which represents a scenario in which greenhouse gas emissions are strongly reduced in the coming decades, and RCP8.5, with continued high greenhouse gas emissions growth.   Season length is defined as the difference between the first and last dates with at least 10 cm (4 in) of snow-water equivalent at the base of each ski area.  Exactly how snowmaking is incorporated into all of this is a bit unclear.  I'll comment on this later.
 
Let's first have a look at the results.  For brevity, I'll focus solely on changes in downhill ski-season length.  These are averages from the climate model projections and attempt to account for snowmaking.  Not surprisingly, there is a decline in ski season length at most ski areas that increases through the 21st century and is largest for the continued high greenhouse gas emissions growth scenario (RCP8.5).  In general, declines in season length are largest in the Northeast and midwest, and smallest in high-elevation regions of the interior west.  There are a few ski areas, mainly that show increases in season length through 2050 under both scenarios and under the RCP4.5 scenario through 2090.

Source: Wobus et al. (2017)
These regional results are generally in line with my expectations.  Vulnerability of snow and skiing to climate change is greatest in the northeast and warmer regions and elevations of the west.  The greatest resiliency is at colder, high-altitude locations Colorado, Utah, and Wyoming.   This means, for example, that Utah's ski industry has more resiliency than Washington's, but also that Alta and Brighton have more resiliency Sundance.

For those of you who want to know what they found for your ski area, the authors include this information in a supplemental file with the paper online.  For kicks, I decided to check out what they found for Utah and got a bit of a chuckle.  Amongst the ski areas were "Park City Ski Area" and "Park City West Ski Area."  Apparently they are using a database that is quite old for ski area information.  But who can blame them for confusion on what to call Park Wolf Canyon City Mountain Resort?  In addition, Alta was not included.  No worries.  God has ensured that great skiing will continue there even in a warming climate.

I would caution, however, in using these numbers quantitatively.  It is my view that this study is most useful in providing qualitative guidance for how ski regions might fare under climate change.  Predictions for specific ski areas should be used cautiously for several reasons.  First, validation of their technique for season length during past years (2004-2010) shows some ability to predict season length geographically, but the scatter for individual stations is fairly large.
Source: Wobus et al. (2017)
Second, they provide only an average, and there are variations in season length amongst the various climate model projections and uncertainties in both the rate of change of temperature and precipitation that must be considered and ultimately mean a range of possible outcomes must be considered.  There is strong consensus amongst scientists and models that temperature will increase in the coming decades, but no real consensus concerning precipitation.  For example, some locations may be able to offset declines in season length due to increasing temperature if precipitation and snowfall increases, but season length will suffer even further if snowfall decreases.

Even with the various warts and caveats that any study of this type has inevitably, the long-term big picture is one of concern for snow lovers.  I see a future in which the differences between the haves and have nots grows.  The decline of snow will be faster in regions and locations that already have marginal conditions and slower in those areas that generally have good conditions.

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