Oversnow vehicle recreation contributes to rural
economies but requires a minimum snow depth to mitigate negative impacts on
the environment. Daily snow water equivalent (SWE) observations from weather
stations in the Lake Tahoe region (western USA) and a SWE reanalysis product
are used to estimate the onset dates of SWE corresponding to
Ongoing and projected climate change is accelerating the warming of the cryosphere throughout Earth's mountain regions (Huss et al., 2017). Reductions in winter season snow, ice, and permafrost cover and volume primarily result from rising air temperatures (Brown and Mote, 2009) and shifts in precipitation from snow to rain (McCabe et al., 2018). These changes have cascading effects from mountains to lowlands with wide-ranging socioeconomic and ecologic impacts (Huss et al., 2017). In mountain regions of the United States, Europe, and Canada, winter recreation and tourism are central to economic activity. The economic benefits from winter recreation are projected to decline as a result of continued climate change that reduces season length and makes access to reliable snow more difficult (McBoyle et al., 2007; Scott et al., 2008; Wobus et al., 2017; Steiger et al., 2017).
Most winter tourism-based climate change impact studies have focused on ski-resort-related activity (Steiger et al., 2017), although research has begun
to address how other recreation-based components of the winter economy may
be affected (McBoyle et al., 2007; Scott et al., 2008; Tercek and Rodman,
2016; Wobus et al., 2017, Hagenstad et al. 2018). Skier visits are
positively correlated to snowfall (Hagenstad et al., 2018) and we assume
that such a correlation is consistent across winter recreation activities.
Due to the dependence on natural snowfall and reduced adaptive capacity
compared to the ski community, which can use cost-effective snowmaking to
augment the natural snowpack, oversnow vehicle (OSV) recreation is highly
vulnerable to climate variability and change (McBoyle et al., 2007; Scott et
al., 2008). Climate change projections for Canada and the northeastern
US under an aggressive greenhouse gas emissions scenario suggest
that by the mid-21st century, OSV season lengths will be reduced by
50 %–100 % in most areas (McBoyle et al., 2007; Scott et al., 2008). A survey
of the OSV community in Vermont found that reductions in the length of the
winter season with sufficient snow coverage for OSV use were observed by
45 % of respondents, with 74 % of respondents decreasing their OSV use
in response to low snow conditions (Perry et al., 2018). This survey also
found that encounters with other recreationists, including OSV users,
detracted from a high-quality recreation experience. The net effects of
reduced season length, more congestion, and lower-quality experiences result
in lower economic benefits from consumer surplus, or the amount a person is
willing to pay over the amount actually spent. For OSVs, consumer surplus is
estimated to be approximately USD 61 person
In the Lake Tahoe region of California (Fig. 1a), and many other rural mountain areas of the western US, OSV use is a regionally significant component of winter season recreation. Estimates of annual economic impact from OSV recreation in the United States range between USD 7 and 26 billion (Fassnacht et al., 2018). As a result, OSV recreation has an appreciable economic impact on rural counties within the northern Sierra Nevada, many of which have a greater dependence on tourism-related employment than elsewhere in California (United States Census, 2016).
The proximity of the Lake Tahoe region to large population centers creates demand for OSV recreation over a limited and ecologically sensitive area. In order to limit potential negative impacts on natural resources (e.g., Keddy et al., 1979) during OSV operation, a minimum snow depth must be present. Minimum snow depth restrictions have been proposed by several forests undergoing winter travel management planning across the Sierra Nevada. This restriction is usually proposed as a minimum depth of 30 cm of un-compacted snow (USFS, 2013). Few forests have such a requirement at this time, but several are currently engaging in the process of winter travel management planning in response to a 2015 US federal court ruling (Federal Register, 2015). The Eldorado National Forest in northern California (located in the southwestern quadrant of the study area) currently requires a minimum snow depth of approximately 30 cm for off-trail OSV use.
To our knowledge, no precise value of this minimum depth has been established through comprehensive studies quantifying OSV use and impacts or disturbance. Nonetheless, evidence indicates that OSV use can alter the landscape when a shallow snowpack is present. Keddy et al. (1979) observed that OSV use on very shallow snow (10–20 cm deep) doubled snow density and compressed underlying vegetation. When OSV use began under a deeper snowpack, less difference in snow density and hardness was observed compared to a control (no-OSV use) snowpack (Fassnacht et al., 2018). Further complicating the minimum depth requirement is the dependence of snow depth on the density of the snow, which varies seasonally and as a function of weather conditions that drive snowpack metamorphism processes (Sturm et al., 2010).
Resource managers tasked with day-to-day operations such as opening and closing OSV trailheads over large, diverse areas may not have the resources to visit trailheads to obtain snow depth and density measurements. Instead, they often rely on subjectively based qualitative assessments of what is deemed sufficient snow. Managers often do not set a specific OSV season, leaving it to user discretion to determine when OSV use is appropriate. This can potentially cause conflict with other uses during the start and end to the winter season and can allow opportunities for inadvertent damage to natural resources due to insufficient snow depth. Here, we estimate the median timing of achieving sufficient snow depths for OSV operation and their trends during the past 34 years using observations of snow water equivalent (SWE) and a reasonable assumption of snow density. We focus on the initial timing of sufficient snow depth since the greatest demands for OSV recreation and potential ecological impacts occur between early and middle winter. The proximal causes of the identified increasingly later onset of achieving a minimum SWE value are further investigated. Because the trend towards later onset is not expected to reverse under continued regional warming, we provide adaptation strategies to cope with diminishing early season snowpack resources that can be included in forest travel management plans. The techniques can be extended to other regions where OSV recreation is an important component of economic activity and where early winter snowpack losses may be impacting seasonal recreation.
The study area is the Lake Tahoe region of the western US, a
coastal moderate-elevation snow-dominated mountain range (Fig. 1a). Daily
maximum and minimum temperature, SWE, and precipitation were acquired for 16
SNOTEL stations from the Natural Resources Conservation Service (
No accepted value of a minimum snow depth exists for OSV operation.
Anecdotal values used by managers vary between 15 and 45 cm depending on
compaction (USFS, 2013), but these do not take into account variability in
snow density. To provide a conservative and reasonable estimate of
sufficient snow depth for what is assumed to be required for non-intrusive
OSV operation, we specified 90 mm SWE (hereafter SWE
To explore possible processes controlling the onset date of SWE
For all data, linear fits were estimated using a Theil–Sen slope and we report Spearman rank correlations. Statistical significance was tested using a modified Mann–Kendall test that accounts for serial correlation (see Hatchett et al., 2017, and references therein).
Adaptation strategies to address loss of early winter snowpack for OSV recreation.
Median timing of achieving SWE
The increasingly later onset of SWE
Due to its moderate elevation, the Lake Tahoe region is susceptible to
climate-change-induced warming (Walton et al., 2017). Our results provide
another metric (later onset date of SWE
Developing a suite of adaptive management strategies is essential if land managers are to meet legal obligations to manage OSV recreation in a manner that minimizes impacts to natural resources, wildlife, and conflict among uses (Federal Register, 2015). As snow seasons become more variable and less dependable overall, it will be necessary to utilize several complementary management strategies if land managers want to continue to provide high-quality opportunities for all forms of winter recreation. For example, setting season dates that encompass the general times of the year when OSV use is appropriate, paired with a minimum SWE (or snow depth, depending on data availability), and allowing for OSV use on certain routes with a lower snowpack to provide access to higher-elevation areas may help to extend the OSV season. Likewise, it may be necessary to relocate winter trailheads to higher elevations as areas with consistent snowpack become shifted upwards in elevation. As the strategies in Table 1 show, however, there are trade-offs with any strategy and OSV recreation is not the sole use of public lands in winter. Managing OSV recreation must occur in concert with managing other forms of winter recreation and protecting wildlife and natural resources (Federal Register, 2015). There is no one-size-fits-all strategy that will work for every national forest. It is essential that land managers work with public and agency stakeholders to craft locally appropriate and equitable adaptation measures, taking into account potential impacts on and conflicts with other recreation uses, wildlife, natural resources, and other land management goals. It may also be necessary to accept that in the future, OSV and other forms of winter recreation (e.g., backcountry skiing and snowshoeing) will not be supported across all of the areas where it historically occurred. Winter travel planning is thus an excellent opportunity for land managers, particularly the US Forest Service, to proactively address OSV management and consider how climate change is affecting OSV activities in national forests in order to maintain the opportunity for this form of winter recreation and its positive economic impact.
Using snow water equivalent and a density assumption as a proxy for depth, we have presented a pilot study aimed at a better understanding of when the Lake Tahoe region attains sufficient snowpack depth to allow safe oversnow vehicle (OSV) usage. A station-based analysis of 16 remote weather stations in the region and a spatially distributed SWE reanalysis product indicated that the median timing of achieving sufficient depth varies with elevation from early November to late December. The median timing of sufficient depth has increased by approximately 2 weeks during the past 3 decades with significant changes on the order of 3 weeks. The proximal causes for this shift towards later onset appear to be due to both a shift from snowfall to rainfall and increases in dry day frequency and temperature during the early winter season. However, further research is needed to estimate specific contributions from each cause and constrain the role of surface-albedo and/or humidity feedbacks at various elevations throughout the region (Patterson, 2016; Walton et al., 2017).
A primary limitation of our study is the lack of an established snow depth to avoid negative impacts of OSV operation as a function of land cover type and snow density. The work of Fassnacht et al. (2018) represents an important advance towards achieving this value, which can be used to guide winter travel management planning, although the US Forest Service has begun to recommend a snow depth (USFS, 2013). Additional studies on achieving regionally relevant minimum snow depths and better quantification of economic and ecological impacts from reduced-snow-cover area and duration will guide more robust travel management plans in national forests. They can also help prioritize pragmatic adaptation strategies for specific regions. Given the economic impact of OSV recreation and likely reduction in land available for OSV or other human-powered recreation uses (McBoyle et al., 2007; Scott et al., 2008; Tercek and Rodman, 2016; Hagenstad et al., 2018), combined with increasing numbers of winter recreation participants (Fassnacht et al., 2018), achieving winter travel management plans that are adaptive to varying snowpack conditions while minimizing user conflicts will be a key step towards sustainable mountain recreation.
Data from the SNOTEL network are available via the US Natural Resources and Conservation Service website:
BJH and HGE conceived and designed the study, interpreted the results, and wrote the paper. BJH acquired data and performed the analysis.
Hilary G. Eisen is employed by the Winter Wildlands Alliance (WWA). Benjamin J. Hatchett has consulted for the WWA.
The project described in this publication was supported by grant number G14AP0076 from the US Geological Survey (USGS). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USGS. This paper was submitted for publication with the understanding that the US Government is authorized to reproduce and distribute reprints for governmental purposes. We greatly appreciate the constructive review comments by Glenn Patterson, Daniel Scott, and Editor Ross Brown that helped us improve the quality of this paper. Edited by: Ross Brown Reviewed by: Glenn Patterson and Daniel Scott