Feasibility study on roof rainwater utilization in seven geographical areas of China based on the precipitation data in recent 40 years

Rainwater utilization is an effective way to solve urban water resources crisis and alleviate urban waterlogging. Precipitation characteristics and rainwater utilization reliability are key indicators to measure the feasibility of rainwater utilization projects. Based on the rainfall data (from 1980 to 2020) from various monitoring stations in China, the precipitation characteristics of 7 geographical regions were analyzed. Using the principle of water balance, a daily precipitation-water consumption balance model was established, the influencing factors of roof rainwater utilization was discussed and the rainwater utilization feasibility of 7 typical cities in 7 geographical regions was analyzed. The results showed that: 1) the average annual rainfall depth decreased gradually from southeast to northwest in China due to the impact of terrain and climate differences. The spatial distribution trend of seasonal and annual rainfall depth was consistent. The seasonal rainfall was the highest in summer, followed by spring and autumn. The distribution characteristics of rainfall concentration were different from that of rainfall, and rainfall was more concentrated in areas with less annual rainfall depth. 2) Precipitation characteristics, rainwater harvesting tank volume, rainwater harvesting area, daily water demand, water saving efficiency and overflow rate had significant influence on the reliability of rainwater utilization in different areas. The greater the rainfall depth, the higher the reliability. The reliability order of the seven typical cities was Guangzhou > Wuhan > Nanjing > Kunming > Harbin > Beijing > Xining, but the reliability of each city could not reach 100%. 3) With the increase of the rainwater harvesting tank volume, the reliability of rainwater utilization increased. However, when the volume of rainwater harvesting tank reached 10 m³, the increase in reliability significantly slowed down. The reliability of rainwater utilization was directly proportional to rainwater collection area and inversely proportional to daily water demand. The curve trend change of water saving efficiency was accordant with that of reliability, but the value was higher than that of reliability. Reasonable control of overflow rate can improve the efficiency of rainwater utilization. In practical applications, both reliability and overflow rate should be considered to determine the optimal size of rainwater harvesting tanks. In general, the feasibility of rainwater utilization is higher in South China, East China and Southwest China, followed by Northeast China and North China, and the lowest in Northwest China.