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With the rapid development of urbanization, more and more cities are facing the risk of flood disasters and the threat of water environment safety during the rainy season. Sponge City, as a new urban water resources management method, has attracted extensive attention in the academic circle. In order to promote the development of Sponge City, a bibliometric analysis method based on Web of Science (WoS) database and Bibliometrix tool is proposed in this study. After refining the retrieved 26,383 papers, 1456 papers were obtained. All the article information including author, keywords and publication time was downloaded. The bibliometric analysis model was established to analyse and discuss the development of Sponge City and related researches during the period 1998-020 (data up to 15 August 2020). Research performance, research focus and development trend were displayed by bibliometric measurement indicators and visual graphics. The results show that the number of research papers on Sponge City has been increased year by year in the past 10 years (2010-2020). Sponge City and related research are increasing rapidly, and the top five countries in terms of research volume are China, the United States, the United Kingdom, South Korea and Canada. China, the United States, the United Kingdom and Australia are the countries with the most extensive international cooperation in the field of Sponge City. Keywords such as 'Sponge City', 'LID (Low Impact Development)' and 'SWMM (Storm Water Management Model)' appeared frequently. In our opinions, interdisciplinary research methods, digital information management technology and comprehensive performance evaluation are the hot research directions for Sponge City in the future. This study aims to provide directions for future research on Sponge City, as well as scientific guidance and reference for government decision makers on Sponge City.

Although the scienti c investigation into ood hazard assessment (FHA) has increased in recent years, a global analysis of FHA-related studies is still rare. This research aims to elucidate trends in FHA-related scienti c inquiry from a quantitative perspective. A bibliometric analysis was conducted to analyze a sample of 723 articles published in the period 2000-2020 from the Web of Science databases (WoS). Bibliometrix R-Tool was used to explore the trends and themes in this eld by analyzing substantial documents, sources, and authors. Results show a growing number of scienti c publications during the past two decades and a poor collaboration network between countries in this eld. Keyword analysis shows that the themes of this research domain were focused on modeling. The main nding is that FHA remains an under-investigation eld of study that focuses on speci c geographical areas. Nevertheless, international collaborations present an increasing trend in FHArelated research, and a growing number of scholars have signi cant interests in FHA, whose topics are gradually systematized. These ndings offer a comprehensive picture of FHA-related research and suggest the need for and bene ts of collaboration across geographical study areas.

As an essential part of the hydrological cycle, precipitation is usually associated with floods and droughts and is increasingly being paid attention to in the context of global warming. Analyzing the change trends and correlation of temperature and extreme precipitation indicators can effectively identify natural disasters. This study aimed to detect the correlation and change trends of temperature and extreme precipitation indicators in Inner Mongolia from 1960 to 2019. Panel vector autoregression (PVAR) models based on Stata software were used to detect the correlation between temperature and extreme precipitation indicators at 35 climatological stations throughout Inner Mongolia. The temperature and extreme precipitation indicator trends were analyzed using the Mann–Kendall test and Sen’s slope method. The spatial distribution characteristics of the annual precipitation and rainfall intensity were more significant in the southeast and more minor in the northwest, while an increase in the annual wet days was noticeable to the northeast. The Granger cause tests of the temperature and the extreme precipitation indicators showed a correlation between each indicator and temperature at the significance level of 1%. The temperature positively correlated with only the rainfall intensity while negatively correlating with the remaining indicators. There is no doubt that trend analysis showed significant increasing trends in rainfall intensity at all stations, which means increased risk in extreme precipitation events. By contrast, the annual precipitation and annual wet days showed significant decreasing trends, which means that the precipitation is concentrated, and it is easier to form extreme precipitation events. The study can provide a basis for decision-making in water resources and drought/flood risk management in Inner Mongolia, China.

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