*Editorial* **A Summary of China's Water Security Status and Issues from a Special Issue**

**Qiting Zuo 1,2 , Fuqiang Wang 3 , Jiaqi Zhai 4 , Xiuyu Zhang 3 , Dunxian She 5 , Lei Zou 6 , Rong Gan 1 and Zengliang Luo 7,\***

Affected by global climate change and rapid socio-economic development, China faces serious water security issues, especially in terms of water shortages, flood disasters, and water-related ecological and environmental problems. These challenges associated with China's water issues have restricted the country's social and economic development, and attracted global attention. Due to the complexity of the water-related issues in China, the solution to these requires comprehensive research across different disciplines.

A series of academic exchanges have been carried out to discuss China's water issues, including the well-known "China Water Forum", which focuses on discussing solutions to China's water issues, the "Water Science Development Forum", which focuses on promoting the multidisciplinary integration of water science and other relevant disciplines to discuss water issues in China, and the "Water Science Lectures", which is an open, shared and non-profit public welfare lecture.

In order to better discuss China's water issues, the Editorial Department of *Water* cooperated with "China Water Forum", "Water Science Development Forum", and "Water Science Lectures" to set up a series of columns. At least one column is planned each year currently. The column established in 2022, "China Water Forum 2022", has ended and the new column set up in 2023, namely "China Water Forum 2023", has begun. A total of 11 papers were accepted in the column "China Water Forum 2022". According to the papers published in the column, we summarize China's water security status and issues to help readers understand the relevant research progress.

Four themes are designed in "China Water Forum 2022", as follows:

The eleven papers published in this Special Issue discuss China's water issues from different aspects. They were divided into three categories based on their research themes, including Category A: "the groundwater issues in parts of China" [1,2], Category B: "the water ecological and environmental issues of rivers and lakes" [3–6], and Category C: "the sustainable utilization of water resources and human–water sustainable development" [7–11].

For Category A, "The groundwater issues in parts of China", Wang et al. [1] set up a numerical model to simulate the saltwater upconing and recovery process in a small coral

**Citation:** Zuo, Q.; Wang, F.; Zhai, J.; Zhang, X.; She, D.; Zou, L.; Gan, R.; Luo, Z. A Summary of China's Water Security Status and Issues from a Special Issue. *Water* **2023**, *15*, 1628. https://doi.org/10.3390/w15081628

Received: 28 March 2023 Accepted: 5 April 2023 Published: 21 April 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

island located on the Xisha Islands in the South China Sea to determine the exploitable coefficient of the freshwater lens in the island. They concluded that the exploitable coefficient of the freshwater lens in the small coral island is smaller than that in inland areas. Wu et al. [2] compared the performance of data-driven models to predict groundwater level with Hebei Plain as a case study. Their results showed that the gated recurrent unit model performed better than other data-driven models such as the support vector machine, long-short term memory, and multi-layer perceptron. Therefore, the determination of ground water level is worth exploring further in the future. The combination of data-driven and physics-based models may help to achieve better results.

For Category B, "The water ecological and environmental issues of rivers and lakes", Lu et al. [3] calculated the minimum lake water demand in East Juyan Lake, an inland desert terminal lake of the Heihe River in northwest China. They found that the area of the lake has increased over the past 15 years due to artificially ecological water diversion. A minimum annual water demand of 54 × 106 m3/year was suggested for the lake; however, it is not currently satisfied. The results of Gao et al. [4] showed that silt contributes the most to lake sediment in the Hulun Lake, China, followed by sand. Zhang et al. [5] investigated the characterization of dissolved organic matter of sediments in streams of the Wuhan City. They showed a considerable impact of heavy metals on the characterization of dissolved organic matter concentrations and components. Liu et al. [6] proved an annual production flow reduction of about −28.2% in the Songhua River Basin under climate change and water use. The contribution of climate change and water use to annual runoff reduction is 77.0% and 23.0%, respectively. They also found that groundwater recharge increased by 9.2% and 4.1% during the freezing and thawing periods in the Songhua River Basin. According to the published papers, water ecological and environmental issues in rivers and lakes of China are still urgent problems to be solved. In detail, the most popular topics of discussion are ecological water demand, water pollutions, and streamflow alteration induced by climate change and human activities.

With regard to Category C, "The sustainable utilization of water resources and humanwater sustainable development", Zuo et al. [7] proposed a carbon dioxide emission equivalent analysis method to quantify the carbon dioxide emission equivalent in 31 provinces in China. The results showed that reservoir storage, tap water allocation, and wastewater treatment are the main contributors to carbon dioxide emissions equivalent for water resource development, allocation, and protection behaviors, respectively. They suggest that increasing the proportion of hydroelectric power generation, improving ecological water security capacity, and strengthening the level of wastewater treatment and reclaimed water reuse are effective measures to promote carbon neutrality. Liang et al. [8] established a green development-level evaluation system to assess the green development of the Chengdu–Chongqing City Group. They showed that the overall green development level of the Chengdu–Chongqing City Group is on an upward trend. Li et al. [9] assessed the harmony degree and adaptive utilization capacity of water resources for sub-systems of water resources, economy, society, and ecology in the Tarim River Basin. They showed that the main factors affecting the harmony development and the adaptive utilization of water resources are per capita GDP, the proportion of non-agricultural output value in GDP, and the per capita net income of rural residents. Zhang et al. [10] analyzed the water-saving level in 31 provinces in China using support vector machine model and found that the water-saving level is high in Beijing City, Henan Province and Zhejiang Province. Overall, the water-saving level in North China, Central China and Southeast China was higher than that in Northwest China, Southwest China and Northeast China. Ju et al. [11] discussed the concept of a happy river. They posit that a happy river should be able to maintain its own health, support high-quality economic and social development in the river basin and the region, reflect harmony between humans and water, and provide people in the river basin with a high sense of security and the ability to gain satisfaction. They further analyzed the meaning of happy rivers from five levels, including water security, water resources, water environment, water ecology, and water culture.

**Author Contributions:** Conceptualization and Writing—Original Draft, Q.Z. and Z.L.; Writing— Review & Editing, F.W., J.Z., X.Z., D.S., L.Z. and R.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Natural Sciences Foundation of China (No. 52279027), and the National Key Research and Development Program of China (No. 2021YFC3200201); Henan International Joint Laboratory of Water Cycle Simulation and Environmental Protection, and Zhengzhou Key Laboratory of Water Resource and Environment.

**Acknowledgments:** The authors acknowledge the contributions of all authors of the eleven papers in this Special Issue.

**Conflicts of Interest:** The authors declare no known conflict of interest.

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