An assessment of satellite remotely-sensed land cover parameters in quantitatively describing the climatic effect of urbanization
The regional-scale climatic impact of urbanization is examined using two land cover parameters, fractional vegetation cover (Fr) and surface moisture availability (M0). The parameters are hypothesized to decrease as surface radiant temperature (T0) increases, forced by vegetation removal and the introduction of non-transpiring, reduced evaporating urban surfaces. Fr and M0 were derived from vegetation index and T0 data computed from the Advanced Very High Resolution Radiometer (AVHRR), and then correlated to a percentage of urban land cover obtained from a supervised classification of Landsat TM imagery. Data from 1985 through 1994 for an area near State College, PA, USA, was utilized. Urban land cover change (at the rate of 3 per cent perkm2 per year) was statistically significant when related to a decrease in normalized values of Fr and increase in normalized values of T0. The relationship between urbanization and M0, however, was ill-defined due to variations in the composition of urban vegetation. From a nomogram of values of Fr and T0, a Land Cover Index (LCI) is proposed, which incorporates the influence of local land cover surrounding urbanized pixels. Such an index could allow changes in land use at neighbourhoodscale to be input in the initialization of atmospheric and hydrological models, as well as provide a new approach for urban heat island analyses. Furthermore, the nomogram can be used to qualify urbanization effects on evapotranspiration rates.
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