Examining the relationship between intermediate-scale soil moisture and terrestrial evaporation within a semi-arid grassland
Interactions between soil moisture and terrestrial evaporation affect water cycle behaviour and responses between the land surface and the atmosphere across scales. With strong heterogeneities at the land surface, the inherent spatial variability in soil moisture makes its representation via poin...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-09-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/20/3987/2016/hess-20-3987-2016.pdf |
| Summary: | Interactions between soil moisture and terrestrial evaporation affect water
cycle behaviour and responses between the land surface and the atmosphere
across scales. With strong heterogeneities at the land surface, the inherent
spatial variability in soil moisture makes its representation via point-scale
measurements challenging, resulting in scale mismatch when compared to
coarser-resolution satellite-based soil moisture or evaporation estimates.
The Cosmic Ray Neutron Probe (CRNP) was developed to address such issues in
the measurement and representation of soil moisture at intermediate scales.
Here, we present a study to assess the utility of CRNP soil moisture
observations in validating model evaporation estimates. The CRNP soil
moisture product from a pasture in the semi-arid central west region of New
South Wales, Australia, was compared to evaporation derived from three
distinct approaches, including the Priestley–Taylor (PT-JPL), Penman–Monteith
(PM-Mu), and Surface Energy Balance System (SEBS) models, driven by forcing
data from local meteorological station data and remote sensing retrievals
from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor.
Pearson's correlations, quantile–quantile (Q–Q) plots, and analysis of
variance (ANOVA) were used to qualitatively and quantitatively evaluate the
temporal distributions of soil moisture and evaporation over the study site.
The relationships were examined against nearly 2 years of observation data,
as well as for different seasons and for defined periods of analysis. Results
highlight that while direct correlations of raw data were not particularly
instructive, the Q–Q plots and ANOVA illustrate that the root-zone soil
moisture represented by the CRNP measurements and the modelled evaporation
estimates reflect similar distributions under most meteorological conditions.
The PT-JPL and PM-Mu model estimates performed contrary to expectation when
high soil moisture and cold temperatures were present, while SEBS model
estimates displayed a disconnect from the soil moisture distribution in
summers with long dry spells. Importantly, no single evaporation model
matched the statistical distribution of the measured soil moisture for the
entire period, highlighting the challenges in effectively capturing
evaporative flux response within changing landscapes. One of the outcomes of
this work is that the analysis points to the feasibility of using
intermediate-scale soil moisture measurements to evaluate gridded estimates
of evaporation, exploiting the independent, yet physically linked nature of
these hydrological variables. |
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| ISSN: | 1027-5606 1607-7938 |