The impact of agricultural practices in China on land-atmosphere interactions

Human-induced land use changes and the resulting alterations in vegetation features are major but poorly recognized drivers of regional climatic patterns. In order to investigate the impacts of anthropogenically-induced seasonal vegetation cover changes on regional climate in China, harmonic analysis is applied to 1982-2000 National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVVHRR)-derived normalized difference vegetation index (NDVI) time series (ten day interval data). For two climatic divisions of South China, it is shown that the first harmonic term is in phase with air temperature, while the second and third harmonics are in phase with agricultural cultivation. The Penman-Monteith Equation and the Complementary Relationship Areal Evapotranspiration (CRAE) model suggest that monthly mean evapotranspiration is out of phase with temperature and precipitation in regions with significant second or third harmonics. Finally, seasonal vegetation cover changes associated with agricultural cultivation are identified: for cropped areas, the temperature and precipitation time series have a single maximum value, while the monthly evapotranspiration time series has a bimodal distribution. It is hypothesized that multi-cropping causes the land surface albedo to sharply increase during harvesting, thereby altering the energy distribution ratio and contributing to observed seasonal vegetation cover changes.