Lessons learned from &ldquoEffects of Land Use Change (LUC) on the Energy and Water Balance of the Semi-Arid Region of Inner Mongolia, China&rdquo
Burkhard
Wilske, University of Toledo, Dept. Environmental Sciences, burkhard.wilske@utoledo.edu
(Presenting)
Nan
Lu, University of Toledo, Dept. Environmental Sciences, nan.lu@utoledo.edu
Ranjeet
John, University of Toledo, Dept. Environmental Sciences, rjohn@utnet.utoledo.edu
Jiquan
Chen, University of Toledo, Dept. Environmental Sciences, jiquan.chen@utoledo.edu
Inner Mongolia, in northern China, encompasses 1.18 million km2 with about 41% being semiarid grasslands. Accelerated land use and land cover changes (LULCC) have dramatically changed the water and energy balances of the region. The primary land use includes overgrazing, agriculture and afforestation. We investigated the biophysical effects of different LUC on water and energy fluxes from eddy-covariance measurements at eight sites. Cultivation decreased ecosystem evapotranspiration (ET) by 15% and 7% during wet and dry years, respectively. Grazing decreased ET by 13% and 0% during wet and dry years, respectively. Reductions in ET were apparently associated with changes in canopy surface conductance, soil water holding capacity and reduced soil moisture. In contrast, large-scale poplar plantations maintained through irrigation or with trees tapping groundwater, increased ET as compared with native shrublands. Water consumption of plantations along the Yellow River may equal 6.5-15% of the mean stream flow and can significantly reduce groundwater levels in the area. Seasonal changes in net radiation (Rn), latent heat (LE), sensible heat (H) and soil heat (G) at cultivated, overgrazed and natural steppe ecosystems showed similar seasonal changes. However, a large decrease in stomatal conductance (gc) obviously limited the LE partitioning of available energy (Rn-G) in these semi-arid ecosystems, with human-disturbed ecosystems showing a decreased LE fraction within a shorter phenological period. Reductions in gc and the decoupling factor (Ω) in the cropland and the degraded steppe suggested that land use could depress latent flux fraction and increases its sensitivity to air and soil drought.
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