Wednesday, 17 January 2007: 4:45 PM
Influences of urbanization on precipitation and water resources in the metropolitan Beijing area
213A (Henry B. Gonzalez Convention Center)
In this study, the analysis of long-term rainfall data collected in the metropolitan Beijing area reveals that the summer rainfall reduction in the northeast areas of Beijing, where the major reservoirs are located, from 1980-2003 is statistically correlated with rapidly urban development in Beijing since 1980. This may be the leading factor for the shortage of water resources in the Beijing area, which has increasingly become a serious factor constraining sustainable economic development. To understand the effects of urbanization on summer rainfall and the potential measures to mitigate such effects, a mesoscale weather/land-surface/urban coupled model and different urban land-use scenarios are used to conduct numerical simulations for a selected heavy summer rainfall event. Results show that urbanization produces less evaporation, higher surface temperatures, larger sensible heat fluxes, and a deeper boundary layer. These modified atmospheric conditions lead to less water vapor, more water-vapor mixing in the boundary layer and hence less convective available potential energy for triggering initiation of convection and rainfall formation. The combination of these factors induced by expanding urban surfaces, results in reduced precipitation for the Beijing area, in general, and for the Miyun reservoir area (the major source for the local water supply), in particular. Increasing the green vegetation coverage in the Beijing area would produce more rainfall, and model results show that planting grass is more effective than planting trees, in this regard. For the same vegetation planted, the rainfall difference from simulations using two green-planting layouts (annular and cuneiform) is small.