Assessing The Impact Of Land Use/Cover Change On Water And Heat Fluxes

Terrestrial ecosystems are influenced by the atmosphere and feedback to the atmosphere,which dynamically maintains the system’s balance by water, heat, momentum and massexchanges. The impacts from human activities on terrestrial ecosystems and globalenvironment are becoming more and more grievous. Landuse and landcover change （LUCC） isan assignable way impacting terrestrial ecosystems and regional environments, which may bealter the distribution of the land surface water and heat flux for the changes from surfacebiophysical properties parameters, such as albedo, leaf area index. To discover the relationsbetween LUCC and the flux of water and heat is the foundation to understand the influencemechanisms of LUCC on ecolosystems. Meanwhile it is important and meaningful tosustainably utilize and manage the regional land and water resources and the relative scientificdecision-making.The geographic information system （GIS） and remote sensing （RS） techniques wereapplied to prepare and analysis the data. An ecosystem process model, GLOPEM-CEVSA wasdriven to simulate the land surface net radiation, evapotranspiration, Bowen ratio and otherhydrothermal parameters. Jiangxi Province, experienced an extensive afforestation andreforestation, was selected as the study area. The purpose of this research is to discover thedifference of the hydrothermal parameters of the varieties of land use types, so as to confirmthe mechanism of LUCC to influence the water and heat fluxes of land surface. The mainresults and conclusions are as follows.Firstly, the meteorological data was interpolated and the land use and cover was mergered.The meteorological data from80stations was interpolated to spatial grid through ANUSPLINsoftware and the data included temperature, precipitation, wind speed and sunshine. The landuse/cover data interpreted from Landsat remote sensing was mergered with the land use/coverproduct （MOD12） of the moderate-resolution imaging spectrometer （MODIS）. The both datawere used to drive the model, GLOPEM-CEVSA. Secondly, the GLOPEM-CEVSA model was ran and outputed the net radiation（Rn）,evapotranspiration（ET）, latent heat （LE）,sensible heat（H） and Bowen ratio（β） for the furtheranalysis after the model was tested with the observed data on the eddy covariance tower in theever-green needle leaf platation at Qianyanzhou station.Thirdly, the sensibility of the model was analized to test the response of Rn and ET to theone of themain biophysical parameters, surface albedo, onsite and regional scale. The albedowas varied as±20%and±10%to simulate the variability of Rn and ET. The results showed ifthe albedo decreased or increased10%, the annual ET will increase15.8mm（2%） and decrease16.8mm（2.12%）, and the annual Rn will increase79.9MJm^-2（2.42%） and decrease81.1MJm^-2（2.46%） on the site scale. If the albedo respectively decreased and increased20%, the annualET will increase25.5mm（3.21%） and decrease16.3mm（3.36%）,and the annual Rn willincrease189.4MJm^-2（5.74%） and decrease195.0MJm^-2（5.91%） on the site scale. On theregional scale, the net radiation （Rn） and the evaportranspitation （ET） showed very differentspatial various under the±20%changes from the albedo.Fourthly, the evaportranspitation （ET） of the different land cover type showed somedifference, however, evergreen broad-leaved forest has the maximum ET （838.0mm） followedby evergreen coniferous forest（830.8mm）, the mixed coniferous （805.3mm）, shrub （802.7mm）,crop （750.9mm） and grass （720.6mm）. The dryness index, the ratio of ET to precipitation, ofdifferent land cover type was statisted according to the area with the less, normal and moreprecipitation amount. And the dryness where evergreen broadleaf forest is planted was highestand followed crop and grass area. The latent heat （LE） and sensible heat （H） of the differentvegetation types showed the same distribution. The Bowen ratio （） presentes the maximum inwoodland, the next is crop and the minimum in grass land. We concluded that woodland ismore conducive to hydrothermal circulation between land and atmosphere, while grassland ismore conducive to warm local climate.Finally, the effects of afforestation, one of major activity related to land use and landcover （LUCC）, was analyzed with the LUCC data in two periods and the model. Theforestation, that is, land cover changed from grass or crop to forest, results the lower albedothan the before land surface and reflects the less solar energy to atmosphere. By higher leafarea index, forest has higher evaportranspitation and makes more moisture local environment, which was quantified in this research.