Hydrological response of a headwater catchment in southeastern Brazil
Part II: Estimate of evapotranspiration with micrometeorological and
water budget methods
Abstract
We estimated the seasonal patterns of evapotranspiration (ET) using
measured field data in a typical headwater basin and four sub-basins, in
subtropical climate region of Serra da Mantiqueira/South-East Brazil,
with a multi-instrument hydrometeorological set (standard weather
station variables, discharge, soil moisture, and surface-atmosphere
turbulent fluxes), towards providing regional data, to our knowledge,
hitherto non-existent, of independent ET from micrometeorological
methods (eddy covariance EC and Bowen ratio BR), energy balance closure
corrections, and water budget based modelling, to discuss the magnitude
and seasonality of the most accurate ET possible to be obtained. We had
an unsatisfactory closure of the energy balance for the EC method, and
the BR method likely also did not meet satisfactory estimates, as both
suffered from the non-ideal conditions of the experimental site imposed
by secondary atmospheric circulations. The comparison of the mean annual
ET among 3 correction methods with the water budget showed an agreement
in the range from 2.6 to 2.9 mm d −1, that was
particularly met by the approaches of Mauder et al. (2013) and Twine et
al. (2001), of 2.8 mm d −1. These corrections
respected upper limits of potential evapotranspiration. Nighttime
corrections were not applied, that possibly explains how daily totals of
the H + LE sum overestimated about 9% of the available energy, that led
to an overestimated ET of roughly less than 5% by those corrections.
The seasonal variability of ET ranged from the minimum of 1.3 mm d-1 in
July, and high fluxes in the wet season of about 3.5 mm d-1. The maximum
H flux in September indicated how the onset of rainfall and the quick
response of soil moisture recovery prevented H to increase onwards on
the rhythm of radiation. Soil moisture appeared to play a key role in
not only ET but in controlling the energy partition.