Abstract. With increasing crop water demands and drought threats, mapping and
monitoring of cropland evapotranspiration (ET) at high spatial and temporal
resolutions become increasingly critical for water management and
sustainability. However, estimating ET from satellites for precise water
resource management is still challenging due to the limitations in both
existing ET models and satellite input data. Specifically, the process of ET
is complex and difficult to model, and existing satellite remote-sensing data
could not fulfill high resolutions in both space and time. To address the
above two issues, this study presents a new high spatiotemporal resolution ET
mapping framework, i.e., BESS-STAIR, which integrates a satellite-driven
water–carbon–energy coupled biophysical model, BESS (Breathing Earth System
Simulator), with a generic and fully automated fusion algorithm, STAIR
(SaTallite dAta IntegRation). In this framework, STAIR provides daily 30 m
multispectral surface reflectance by fusing Landsat and MODIS satellite data
to derive a fine-resolution leaf area index and visible/near-infrared albedo,
all of which, along with coarse-resolution meteorological and CO2
data, are used to drive BESS to estimate gap-free 30 m resolution daily ET.
We applied BESS-STAIR from 2000 through 2017 in six areas across the US Corn
Belt and validated BESS-STAIR ET estimations using flux-tower measurements
over 12 sites (85 site years). Results showed that BESS-STAIR daily ET
achieved an overall R2=0.75, with root mean square error RMSE =0.93 mm d−1 and relative error RE =27.9 % when benchmarked
with the flux measurements. In addition, BESS-STAIR ET estimations captured
the spatial patterns, seasonal cycles, and interannual dynamics well in
different sub-regions. The high performance of the BESS-STAIR framework
primarily resulted from (1) the implementation of coupled constraints on
water, carbon, and energy in BESS, (2) high-quality daily 30 m data from the
STAIR fusion algorithm, and (3) BESS's applicability under all-sky
conditions. BESS-STAIR is calibration-free and has great potentials to be a
reliable tool for water resource management and precision agriculture
applications for the US Corn Belt and even worldwide given the global
coverage of its input data.