When and where does storage matter for plants: the effect of root zone
water storage capacity on evapotranspiration
Abstract
Root zone water storage capacity (SR) plays a fundamental role in
determining the magnitude of evapotranspiration (ET) during both average
and extreme climatic conditions. While methods exist to estimate SR
globally at relatively fine spatial scales, the effects of uncertainty
in these broad-scale estimates on evapotranspiration are largely
unknown. We present a new method to efficiently describe the
relationships between SR and evapotranspiration across all possible
values of SR, for a given climate. This approach replaces
computationally expensive model sensitivity analyses and provides a
means for characterizing the importance of uncertainty and spatial
variability in SR across various climates and timescales. To demonstrate
the utility of our framework, we apply our approach to nine sites across
the United States that vary in their seasonal climatology. In doing so,
we show that evapotranspiration can be dramatically different between
sites even with the same SR. For example, a very shallow SR (15 mm)
would limit evapotranspiration to 27% of its maximum value (given no
storage limitation) in some sites but to only 68% in others.
Furthermore, if SR was estimated to be 250 mm with an uncertainty of +-
20%, the effect on estimated evapotranspiration in Eel (a site in
Northern California) would be significant (+- 10%) but negligible in
Boulder (a site in the Colorado Rockies). Furthermore, we find distinct
site-specific SR–ET relationships that substantially impact how
uncertainty and spatial variability in landscape distributions of
SRaffect evapotranspiration patterns.