2002 Annual

Thursday, 17 January 2002: 11:00 AM
Influence of land use on the regional climate of southwest Australia
Deepak K. Ray, Foretsry and Natural Resources, Purdue University, West Lafayette, Indiana; and U. S. Nair, R. M. Welch, W. Su, and T. Kikuchi
Poster PDF (103.9 kB)
Since the late 1800s native perennial vegetation in southwestern Australia has been replaced by seasonal winter growing wheat crop. The boundary between the areas cleared for agriculture and native vegetation is more than 700 km long and is easily visible from satellite imagery. The presence of large adjacent areas of differing vegetation types and relatively gentle topography makes this area ideal for investigating the effects of land use on regional climate. This study investigates the differences in top of the atmosphere radiation budget, surface energy budget and cumulus cloud formation between agricultural and native vegetation areas.

CERES (Clouds and Earth's Radiant Energy Budget Scanner) observations show that higher shortwave flux is reflected from agricultural areas. The difference in the amount of top of the atmosphere shortwave between the two vegetation types increases from approximately 30 Wm-2 to 60 Wm-2 from August 2000 to February 2001. However the differences in the values of the top of the atmosphere longwave radiation between agricultural areas and native vegetation is negligible. Thus the net top of the atmosphere radiation is higher over native vegetation compared to agricultural areas.

Using Geosynchronous Meteorological Satellite (GMS-5) data, the diurnal occurrence of cumulus clouds is derived using an automated cumulus detection algorithm for the months of January 1999 to January 2001. Results show that cumulus clouds occur more frequently over native perennial vegetation during the dry summer months but during the winter rainy season the frequency of occurrence is higher over agricultural areas.

Surface moisture availability and energy fluxes are determined using a Soil Vegetation Atmospheric Transfer (SVAT) model in conjunction with Advanced Spaceborne and Thermal Emission Radiometer (ASTER) images. NDVI (Normalized Difference Vegetation Index) derived from ASTER channel 2 (0.63 - 0.69 Ám) and channel 3 (0.76 - 0.86 Ám), and surface radiant temperature from ASTER channel 14 (10.95 - 11.65 Ám) are used for this purpose. Surface energy budget derived from ASTER scenes during the dry season month of November 2000, and January 2001, show higher latent heat and lower sensible heat over native vegetation areas. Field measurements from prior studies (Lyons et. al., 1993), show a reverse pattern during winter months, where higher sensible and lower latent heat fluxes are observed over native vegetation during the peak agricultural season (August). The results suggest that the preferential formation of cumulus clouds appears to be associated with regions of enhanced latent heat flux.

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