Abstract
Climate warming is projected to affect forest water yields but the effects are expected to vary. We investigated how forest type and age affect water yield resilience to climate warming. To answer this question, we examined the variability in historical water yields at long-term experimental catchments across Canada and the United States over 5-year cool and warm periods. Using the theoretical framework of the Budyko curve, we calculated the effects of climate warming on the annual partitioning of precipitation (P) into evapotranspiration (ET) and water yield. Deviation (d) was defined as a catchment's change in actual ET divided by P [AET/P; evaporative index (EI)] coincident with a shift from a cool to a warm period – a positive d indicates an upward shift in EI and smaller than expected water yields, and a negative d indicates a downward shift in EI and larger than expected water yields. Elasticity was defined as the ratio of interannual variation in potential ET divided by P (PET/P; dryness index) to interannual variation in the EI – high elasticity indicates low d despite large range in drying index (i.e., resilient water yields), low elasticity indicates high d despite small range in drying index (i.e., nonresilient water yields). Although the data needed to fully evaluate ecosystems based on these metrics are limited, we were able to identify some characteristics of response among forest types. Alpine sites showed the greatest sensitivity to climate warming with any warming leading to increased water yields. Conifer forests included catchments with lowest elasticity and stable to larger water yields. Deciduous forests included catchments with intermediate elasticity and stable to smaller water yields. Mixed coniferous/deciduous forests included catchments with highest elasticity and stable water yields. Forest type appeared to influence the resilience of catchment water yields to climate warming, with conifer and deciduous catchments more susceptible to climate warming than the more diverse mixed forest catchments.
Highlights
Since the Industrial Revolution, warmer air temperatures have been observed at continental scales (Jansen et al, 2007)
The main difference is that engineering resilience implies a single state, whereas ecological resilience implies a system flip among two or more stable states, all of which reside in a landscape of possible alternatives, and different disciplines have adopted different definitions to describe resilience (Brand & Jax, 2007)
Catchment points falling in close proximity to the curve (|s| < 0.05) indicated prewarming water yields that were consistent with the theoretical predictions of the Budyko curve
Summary
Since the Industrial Revolution, warmer air temperatures have been observed at continental scales (Jansen et al, 2007). Long-term meteorological and hydrological records in headwater catchments, initiated to investigate management effects on hydrological fluxes in the early 20th century, are increasingly valuable for exploration of the effects of climate warming on water supplies. These data indicate that water yield response to climate warming varies among biomes (Jones et al, 2012). Engineering resilience suggests that a system may exist in only one stable equilibrium state; to measure such a system’s resilience, one must determine its resistance to change and the time needed to return to the equilibrium state. The main difference is that engineering resilience implies a single state (the system may be displaced from that state but if it is resilient, it will return to it), whereas ecological resilience implies a system flip among two or more stable states, all of which reside in a landscape of possible alternatives, and different disciplines have adopted different definitions to describe resilience (Brand & Jax, 2007)
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