THE TEMPORAL AND SPATIAL DISTRIBUTION CHARACTERISTICS OF EVAPOTRANSPIRATION AND SENSIBLE HEAT FLUXES AND INFLUENCE FACTORS IN THE YANGTZE DELTA REGION

Evapotranspiration and sensible heat fluxes in Yangtze Delta Region(28-33°N, 118-123°E) are estimated for the past 40 years by modified Kotoda-Bortan(K-B) model and Newton diffusion method respectively. The temporal and spatial distribution characteristics of evapotranspiration and sensible heat fluxes are analyzed combined with land-using data, meteorological data such as air temperature, solar radiation, cloudiness, etc. The results show that the regional averaged evapot ranspiration has at endency of decreasing gradually during the past 40 years. The sensible heat fluxes show no obvious variation in this period. The main reasons for the decrease of evapot ranspiration are considered first to be the variation of cloudiness in this region, which induced the decrease of solar radiation arrived on the ground surface. The second reason is the change of the land use condition. Compared with 1980, the proportion of paddy field, farmland and water surface area were decreased by 1.353%, 4.42% and 2.597% respectively, but urban land non-agriculture area was increased by 3.345% in 1998. The dif ference of evapot ranspiration from various surfaces and the change of land use made the regional averaged evapot ranspiration be decreased.