Author(s): Jia Y.; N. Tamai; Q. Luo; And N. Tanaka
Linked Author(s): Nobuyuki Tamai
Keywords: Urbanization; Water budget; Heat environment; Subgrid heterogeneity; Penman-Monteith equation; Green-Ampt model; Force-Restore method
Abstract: A distributed model of water and heat transfers is described at first. The subgrid heterogeneity of land use is taken into consideration by using a mosaic method. Evapotranspiration and latent heat flux are computed by the Penman-Monteith equation, infiltration excess during heavy rains is simulated by a generalized GreenAmpt model whereas saturation excess during the remaining periods is obtained by balance analysis in unsaturated soil layers. Surface temperature is solved by the Force-Restore method. Then water and heat budgets in 1993 in the Tokyo Metropolitan Area of about 7800km 2 are studied by using the distributed model in a time step of 1 hour and in a grid size of 1km. The land use data and DEM are based on the Fine Digital Information (100m by 100m mesh) of Japan Geography Institute. The meteorological data are based on the 46 AMe DAS stations in the area. Impacts of urbanization on water budgets and heat environment are analyzed by comparison of simulation result of present land use with that of natural land use (approximately 100 years ago). It is found that urbanization gives big impacts on water budgets and heat environment in the study area. For example, annual evapotranspiration decreased to 568mm in present land use from 706mm in past natural land use, the Bowen ratio increased to present 0. 36 from past 0. 12 and surface temperature showed 3~5°C higher in central urban area than in surrounding natural area. In addition, Influences of subgrid heterogeneity of land use on simulation results are also studied by comparison of simulation result of uniform land use scheme with that of mosaic land use scheme. It is found that subgrid heterogeneity of land use gives a quite strong influence on annual water and heat budgets in urbanized area.