# Sustainable Urban Water Management in China: A Case Study from Guangzhou and Kunming
## 3 Case Study Cities in China  
Guangzhou, formerly known as Canton, is Guangdong's capital city, located in southern China near the South Sea on the east bank of the Pearl River. There are around 1300 rivers and 108 ecological parks, which include forest, wetland, and geology parks. Guangzhou, which measures 7434.4 km\({}^{2}\) and has a population of 15.31 million, is one of China's first-tier cities and the Pearl River Delta's commercial hub. Guangzhou's GDP is expected to reach 2.5 trillion Yuan by the year 2020 [29]. Guangzhou's entire wetland area is 86,178 ha, including 39,286.4 ha of wetland near the sea and beach, which accounts for 45.6% of the total. The river wetland area is 10,804.9 ha, accounting for 12.5% of the total. The lake wetland covers 154.3 hectares, whereas the pool wetland covers 35.933 hectares, respectively [30]. The salinity of Pearl River water has remained low [31]. Yuzhu Pier's yearly average salinity is greater than that of upstream Zhongda Pier, which is 0.22 [32]. From April to November every year, Guangzhou's old town floods as a result of typhoons that bring heavy rainfall and strong winds throughout the rainy season. According to the Guangzhou Meteorological Service, the city's average cumulative rainfall from 1 March to 8 May hit 791.6 mm, a record high that was 42.9 mm higher than the historical record of 748.7 mm set in 1980 over the same period. The most recent period of extreme rainfall occurred on 19 April 2019. It attained a speed of 75.9 mm/h. Additionally, the water level in the Pearl River increased from 3.07 m to 3.28 m with the passage of the most recent powerful typhoon, 'Super Typhoon Mangkhut, international no. 1822, on 17 November 2018 [33]. According to data from the national climate center, the chance of spring rainfall increased by 24% in Guangzhou [34]. In Guangzhou, sewage is primarily transferred to municipal sewage treatment plants for centralized treatment via the urban pipe network's collecting system and sewage interception system. The drainage system encompasses 7440 km\({}^{2}\) and collects and treats more than 95% of the sewage. In the year 2018, the separate sewage and rainfall systems covered only 42% of Guangzhou, making them the system's weakest link. Additionally, 83% of sewage pipes are constructed for a one-year return time of rainstorm events, whileother pipes in Guangzhou's central business district are only intended for a half-year return period, implying that the occurrence of severe rainfall easily results in floods [35]. Kunming is the provincial capital of Yunnan, and its beautiful tourist attraction is the Dian Lake. It features the characteristic low-latitude plateau mountain monsoon climate, in which the temperature is controlled not only by the season, but also by its elevation. The metropolitan region is located north of Dian Lake and is flanked on all sides by hills and mountains, transforming it into a flat ground [36]. Precipitation is concentrated in Kunming from May to October every year, with the majority of rainfall falling in the low elevation area [37]. The main urban region is prone to heavy rain and flooding due to the effect of the southwestern warm and humid airflow, mountain barriers, and uneven rainfall [38]. Dian Lake is a key supporter of economic development in Kunming, a well-known tourist destination. In the spring season, flocks of red-billed gulls flocks in from the northern seas to seek refuge from the chilly winds. In recent years, the favorable economic climate and inexpensive housing prices have attracted an increasing number of young talents. The overall population is >4.3 million in the year 2021, with a third of the population made up of migrating citizens, resulting in new environmental pressures. The Dian Lake is a 330 km\({}^{2}\) plateau based freshwater lake in China. It is also the confluence of 35 rivers. Dian Lake is positioned at the lowest elevation; hence, it receives the most of the water from the urban area. As a result, it is critical in resolving several urban water-related issues.