Water in the Balance: Interpreting Climate Change Impacts Using a Water Balance Model

Thoma, David; Rodman, Ann; Tercek, Mike

In Yellowstone, the margin of life is thin but organisms adapted to the mountain environments survive. Long winters and short summers affect resource availability, and disturbances like fire pose other challenges to the persistence of Northern Range species like sagebrush, whitebark pine on Electric Peak, and boreal chorus frogs in a Mount Everts pond. Weather and climate are primary factors tipping the balance between the prosperity and demise of every species. These interactions have played out over thousands of years across a complex landscape and shape the remarkable patterns of floral and faunal biodiversity in Yellowstone today. But the climate is changing. Specifically, spatial and temporal patterns in temperature (T) and precipitation (P) are changing, but they are not changing the same way everywhere. Further complicating changes in climate are topographic factors like soil type and slope aspect that may buffer change at some locations but exacerbate change elsewhere. Additionally, effects are complicated by the different tolerances among species to extreme cold or drought conditions; survival and reproduction of sagebrush may be limited by moisture, whitebark pine may be limited by cold temperatures, and chorus frogs may be limited by both. In the first issue of Yellowstone Science, Bill Romme and Monica Turner (Romme and Turner 1992) discussed possible influences of climate change on Yellowstone vegetation. They noted several future scenarios including hotter-drier, hotter-similar precipitation, and hotterwetter conditions, and described how such changes could affect vegetation, fire regimes, and wildlife in Yellowstone. They used the terms “evapotranspiration,” “water use efficiency,” and “drought stress” in describing the forces that might affect vegetation, wildlife, and fire regimes. Now, more than 22 years later, with an increasing awareness and growing need to understand the impacts of climate change, we use new data sets to explore the effects of changes in T and P on the Northern Range. Our research evaluated the interactions between T and P affecting timing and abundance of water in the environment and the biological communities that depend on water. Romme and Turner’s prescient long-range scenarios covered a range of possible influences, all of which we cannot comment on here. By focusing on the interaction of temperature and precipitation in this article we: 1) describe changes in P and T over the past few decades across the Northern Range, 2) explain how a water balance model integrates T and P in biophysically relevant ways, and 3) run the water balance model and discuss insights gained from exploring the interactions of T and P affecting timing, abundance, and fate of water in the environment with emphasis on evapotranspiration, drought stress, surface runoff, and growing degree days.

Water in the Balance: Interpreting Climate Change Impacts Using a Water Balance Model

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