Velocity of Climate Change and the Vulnerability of Mountain Lake Landscapes

Freshwater ecosystems in mountain landscapes are threatened
by
climate change. Accumulated heat can result in lethal short-term heat
exposure, while velocity of change governs severity and rates of long-term
heat exposure. Here, we novelly integrate heat accumulation and velocity
of change approaches to classify climate-vulnerable USA mountain watersheds.
We combine watershed position and air temperature data to calculate
degree-days. We then calculate the current velocity of this change
and used discriminant function analyses to classify watershed vulnerability
through 2100. Our results demonstrate how rates of heat accumulation
are increasing across mountain landscapes. We estimate 19% of watersheds
are at greatest vulnerability to accumulated heat, and this will increase
to 33% by 2100. Further, mean killing degree days (i.e., region-specific
mean number of days above 90th temperature percentile) are projected
to increase 215–254% (mean = 236%) over this same time frame.
Together, results indicate heat accumulation will increase substantially
over the next 75 years; changes are projected to be most severe in
lower elevation landscapes and those with greatest historical velocity
of change. These changes will likely restructure species’ distributions.
Decision-makers can use these classifications to better understand
landscapes, species’ needs, and ecosystem services, thereby
enabling effective allocation of conservation resources.