Xi'an Rainwater Harvesting Potential And The Utilization Mode

With the acceleration of urbanization and the rapid growth of population, the situation of water deficiency has become very serious for most cities in China. At the same time, flood disasters frequently occur. It is, therefore, necessary to solve water problems through urban rainfall utilization.On the basis of overview of urban rainfall utilization at home and abroad, the potential volume of rainfall for utilization in Xi'an city is estimated, the way and measurements for urban rainfall utilization are also suggested. The main results of this study are summarized as follows:(1) Based on the analyses of characteristics of urban rainfall resources and the relationship between urban water and other forms of water resources, the concept of the regional urban rainfall utilization are proposed and discussed. And the measures for urban rainfall utilization in the center district and surrounding area of a city are put forward, respectively.(2) According to precipitation data from seven gauging stations around Xi'an city during the period 1961-2005, the temporal and spatial distributions of precipitation in Xi'an region are analyzed. The annual and seasonal variations of precipitation are determined using the Mann-Kendall test. The results show that the temporal and spatial distributions of precipitation was uneven and the mean annual precipitation had a decreasing trend from 1961 to 2005, which mainly resulted from the large variation of precipitation during the seasons of spring and autumn, especially during spring, during which the slope is-1.98mm/a. While in the seasons summer and winter, the precipitation exhibited an increasing trend. The rainy season is concentrated during the seasons of summer and autumn of each year, and the rainfall during the period from May to October occupies 79% of the total annual precipitation. Moreover, according to the document of Overall Planning of Land Uses for Xi'an (from 1996 to 2010), the potential amount of rainfall harvesting per capita of Xi'an in a typical year with the probability of 75%(p=75%) is estimated to be 0.93 billion m3. The potential amount of rainfall for utilization in an area within the city ring expressway of Xi'an is estimated on the basis of GIS. It is found that the potential amount of rainfall utilization is 1.14 billion m3, which accounts for 8.1% of the total amount of water consumption in the year of 2005.(3) From analyses of the special characteristic on the rainfall utilization for the different type of city land, an integrated allocation model for the regional urban rainfall utilization is proposed. And the assessment indicator for the effective utilization of the regional urban rainfall resources is introduced as well. Furthermore, the ecological, social and economic values which can be derived from rainfall utilization are estimated. Finally, on the basis of analyses of the correlation of rainfall resources for all type of land and their comprehensive utilization, an effective model for regional rainfall utilization in Xi'an City is suggested.