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Abstract:
The land surface energy and water balances are
tightly coupled by the partitioning of absorbed solar radiation
into terrestrial radiation and the turbulent fluxes of sensible
and latent heat, as well as the partitioning of precipitation
into evaporation and runoff. Evaporation forms the critical
link between these two balances. Its rate is strongly affected
by turbulent exchange as it provides the means to efficiently
exchange moisture between the heated, moist surface and the
cooled, dry atmosphere. Here, we use the constraint that this
mass exchange operates at the thermodynamic limit of maximum
power to derive analytical expressions for the partitioning
of the surface energy and water balances on land.We
use satellite-derived forcing of absorbed solar radiation, surface
temperature and precipitation to derive simple spatial
estimates for the annual mean fluxes of sensible and latent
heat and evaluate these estimates with the ERA-Interim reanalysis
data set and observations of the discharge of large
river basins. Given the extremely simple approach, we find
that our estimates explain the climatic mean variations in net
radiation, evaporation, and river discharge reasonably well.
We conclude that our analytical, minimum approach provides
adequate first order estimates of the surface energy
and water balance on land and that the thermodynamic limit
of maximum power provides a useful closure assumption to constrain the energy partitioning at the land surface.
