Estimating net irrigation across the North China Plain through dual
modelling of evapotranspiration
Abstract
Irrigation is the greatest human interference with the terrestrial water
cycle. Detailed knowledge on irrigation is required to better manage
water resources and to increase water use efficiency (WUE). This study
brings forward a novel framework to quantify net irrigation at monthly
timescale at a spatial resolution of 1 kmproviding unprecedented spatial
and temporal detail. Net irrigation refers to the evaporative loss of
irrigation water. The study is conducted in the Haihe River Basin (HRB)
in China encompassing the North China Plain (NCP), a global hotspot of
groundwater depletion. Net irrigation is estimated based on the
systematic evapotranspiration (ET) residuals between a remote sensing
based model and a hydrologic model that does not include an irrigation
scheme. The results suggest an average annual net irrigation of 126 mm
(15.2 km) for NCP and 108 mm (18.6 km) for HRB. It is found that net
irrigation can be estimated with higher fidelity for winter crops than
for summer crops. The simulated water balance of the HRB was evaluated
with GRACE data and it was found that the net irrigation estimates could
close the water balance gap. Annual winter wheat classifications reveal
an increasing crop area with a trend of 2200 km yr. This trend is not
accompanied by a likewise increasing trend in irrigation, which suggests
an increased WUE in the NCP. The proposed framework can easily be scaled
up or transferred to other regions and support decision makers to tackle
irrigation induced water crises and support sustainable water
management.