Spring snowpack influences in the volume and timing of spring and peak season overnight visitation to Yosemite Wilderness

Abstract

Wilderness visitation, particularly overnight use, is reactive to climate variability as backpackers face greater exposure to and dependence on environmental conditions. This study examines the effect that spring snowpack has on the timing and volume of permits issued for overnight use of the Yosemite Wilderness during peak and shoulder season months (April-October) from 2002-2019. We categorize April 1st snowpack at Tuolumne Meadows into snow drought (<75%), high snowpack (>125%), and near average snowpack (75-125%). Results confirm Wilderness-wide differences between snowpack categories, including change in spring overnight visitors (April-June: +20% snow drought, −28% high snowpack). Our findings confirm that snow drought allows for more access to high elevation trailheads when seasonal roads are open earlier in spring (May-June: +74% Tioga Road, +81% Tuolumne Meadows). Mid-to-high elevation trailheads experience a sustained increase in use during high snowpack years (June-October: +12% Yosemite Valley and Big Oak Flat, +15% Glacier Point Road and Wawona; +32% Hetch Hetchy) as a narrower seasonal access window leads to filled permit quotas in the high country and displaces use to lower elevation trailheads. These findings have implications for wilderness stewards, including biophysical and experiential impacts to wilderness character from earlier and longer seasons, especially at higher elevation and fragile alpine and sub-alpine areas, as snow drought in mountain protected areas becomes more common. Recommendations to address greater early season use and its attendant impacts include adaptively managing permits for different types of snowpack years, including potential changes in the number, timing, and destination of select trailhead quotas.