Land Use Change Impacts on Regional Evapotranspiration and Water Availability
DOI:
https://doi.org/10.5281/zenodo.22815078Keywords:
evapotranspiration, land use change, deforestation, agricultural expansion, water yield, remote sensing, MODIS, Amazon-Cerrado transition, catchment hydrology, water balanceAbstract
Land use change alters the partitioning of precipitation between evapotranspiration (ET) and runoff, with
consequences for downstream water availability that remain incompletely quantified at catchment scale in actively
converting agricultural frontiers. We combined 23 years (2001-2023) of MODIS-based actual evapotranspiration
(MOD16A2, cross-checked against a Priestley-Taylor Jet Propulsion Laboratory estimate), annual MapBiomas
land-cover classifications, and daily discharge records from 34 gauged tributary catchments (820-9,460 km2)
spanning a gradient of forest loss across the southern Amazon-Cerrado agricultural frontier in Mato Grosso, Brazil,
to quantify how forest-to-cropland and forest-to-pasture conversion has altered regional ET and catchment-scale
water availability, including dry-season low flows. Catchments with more than 40 percent forest loss since 2001
showed 14 percent lower mean annual ET (1,042 versus 1,210 mm yr-1) and a 9-percentage-point higher annual
runoff ratio than catchments retaining more than 90 percent forest cover, consistent with reduced canopy
interception and rooting depth following conversion. However, dry-season (June-September) streamflow in
high-conversion catchments declined by an average of 18 percent relative to their own pre-conversion baseline and
to precipitation-matched reference catchments, a pattern not predicted by the annual water balance alone and
attributable to a measurable reduction in dry-season precipitation and delayed wet-season onset associated with
diminished forest-driven moisture recycling. The magnitude of both the annual ET decline and the dry-season flow
deficit depended strongly on the post-conversion land cover: catchments converted to pasture showed a 19 percent
ET decline and a 24 percent dry-season flow reduction, whereas catchments converted to double-cropped
soybean-maize systems, which maintain canopy cover for a longer fraction of the year, showed a smaller 6 percent
ET decline and an 8 percent dry-season flow reduction. A mixed-effects regression confirmed forest-loss fraction
and post-conversion cropping intensity as the two strongest predictors of catchment ET anomaly, together
explaining 61 percent of variance. These findings indicate that agricultural expansion in this region increases
short-term annual water yield through reduced evapotranspiration but simultaneously threatens dry-season water
security through a regional precipitation feedback, and that cropping-system choice, particularly cropping intensity,
is a tractable lever for moderating this trade-off.
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