GIS-based estimation of potential amount of rainwater for utilization in Xi'an City.

With the acceleration of urbanization,surface water has heavily been polluted and groundwater has been over-exploited,the situation of water shortage becomes very serious for most cities in northwest China.Rainwater utilization has been playing a great role in water resource development.Urban rainwater utilization has been caused great attention and well studied by researchers,which has been regarded as the most direct and effective way to supply water resources for urban demand.Xi'an,as the capital of Shaanxi Province,is one of the developed cities in northwest China.However,its development has seriously been affected by the lack of water resources.Analysis of potential amount of rainwater for utilization is of great importance in the sustainable development for Xi'an City.In this study,using GIS method,the potential volume of rainwater for utilization in Xi'an City is estimated.Firstly,the whole land area of Xi'an City is divided into nine land types,which include dry land,road,water area,village,school district,business district,garden land,residential district and resort area.Secondly,the area of each land type is calculated.The total area for the nine land types is 47 245×104 m2.Moreover,according to the related references,the runoff coefficient for each land type is determined,which ranges from 0.2 to 1.0.Finally,on the basis of the precipitation data collected from gauging stations in Xi'an City from 1961 to 2005,the theoretical and actual volume of available rainwater for utilization in a year with the probability 50% of occurrence(p=50%) and that in a year with the probability 75% of occurrence(p=75%) are determined,respectively.The results show that the theoretical volume of available rainwater for utilization in a year with p=50% is 1.6×108 m3 and that in a year with p=75% is 1.3×108 m3.While the actual volume of available rainwater for utilization in a year with p=50% is 1.11×108 m3 and that in a year with p=75% is 0.93×108 m3.Obviously,the available rainwater for utilization in a year with p=50% and a year with p=75% approximately equals to 9.7% and 8.1% of the total amount of water consumption in Xi'an City of 2005,respectively.Among nine types of land,the largest volume of available rainwater for utilization mainly comes from dry land,road and business district.The ratio of the available rainwater for utilization from dry land,road and business district to the total available volume of rainwater is more than 75% in either a year with p=50% or a year with p=75%.It is can be concluded that the potential volume of rainwater for utilization in Xi'an City is very considerable,and its use should be taken into account by government and put into effect.This study provides theoretical reference for the urban rainwater utilization in Xi'an City even in other cities of northwest China.