Urban flood information enables managers to rapidly synthesize comprehensive flood event profiles, serving as critical evidence for flood control decision making. Compared with traditional methods, public data offer unprecedented spatiotemporal granularity due to its high volume, multidimensionality, and real-time nature. In this paper, we investigated public data’s usefulness and generalizability of spatial feature differences using multi-source social media data as an entry point. We selected rainstorm events that occurred in three cities located in the North China Plain, the Southeast Coastal Region, and the Western Region of China, with vastly different developmental statuses in 2023. Then, multi-platform data from the events were collected and analyzed through crawling and topic mining. The results indicate that: (1) social media data from different sources are complementary to each other and can collectively extract plenty of neglected waterlogging points to supplement official data, with a supplementary rate reaching 171% on average; and (2) social media data has significant value in spatial characterization, which means that its availability remains constant despite geographical differences and can self-adapt to local geography, inhabitant profiles and social development levels. To address the issues of limited available data and essential information lacking during the analysis process, we propose recommendations for data processing and city managers to enhance the scientific value of social media data utilized in practice.

Nitrate pollution in groundwater has become a global concern as it can affect the drinking water quality and human health. In this paper, an extensive hydrochemical investigation and health risk were performed in the Subei Lake basin where shallow groundwater is the main available drinking water resource for residents. The prevalent pollutant, nitrate (NO₃^-), has been identified based on descriptive statistical method and box and whisker plots, and most of the other parameters of groundwater samples meet water standards and can be used for drinking purpose. Nearly 23.53% of groundwater samples had the NO₃^- concentrations higher than the limit of 50 mg/L recommended by the World Health Organization, and the extremely high nitrate content (199 mg/L) was distributed around the Mukai Lake. Piper triangle diagram proposed that the dominated anions of hydrochemical types were observed with a gradual evolving trend from HCO₃^- to SO₄^2- and Cl^- with the increase of nitrate content. The results of correspondence analysis showed that agricultural activities were the most the possible source of nitrate contamination, while the higher content of other parameters in individual groundwater samples may be controlled by natural factors. The impacts of pollutant NO₃^- on human health were quantified using health risk assessment model, and results showed that the order of non-carcinogenic health risk values from oral exposure was Infants＞Children＞Adult males＞Adult females, corresponding to 65%, 53%, 41% and 35% of samples exceeding the accepted limit for nitrate associated health risk (HQ＞1), respectively. The detailed knowledge on groundwater quality characteristics obtained from this study can provide valuable reference for drinking water safety and groundwater pollution prevention.