Hang Zhou

Groundwater is a vital resource for human activities, and its level changes influence the depth design and operation of wells. This study analyzed the Hebei Plain using 1127 boreholes to delineate aquifers I–IV via Kriging interpolation. Groundwater and wells were classified. Utilizing over 120,000 wells, this study analyzed depth trends for shallow/deep wells, developed well-depth models, and examined type correlation, while evaluating adjustments in new well depths in response to groundwater level changes. The results reveal shallow groundwater depth decreased by 0.29 m/yr from 2005 to 2019, reaching 73.84 m, and then rebounded 1.22 m/yr during 2019–2021 to 15.27 m; deep groundwater depth declined continuously at 0.78 m/yr over 2005–2021, reaching 105.82 m. Well-depth models show shallow well depths increased over time (peaking at 77.26 m) but project future declines, while deep wells exhibited continuous depth reduction (minimum 180.33 m) with ongoing decrease expected. The sensitivity of newly constructed well depths to groundwater fluctuations had the following order: rural domestic > agricultural > industrial for shallow wells, and agricultural > rural domestic > industrial for deep wells. This study informs future well-depth planning near overexploited zones and supports well optimization, irrigation management, strategy adjustment, and groundwater conservation.

Extreme climate events are occurring frequently under global warming. Previous studies primarily focused on isolated extreme climate events, whereas research on the synergistic changes between extreme cold (EC) and extreme warm (EW) events remains limited. This study conducted trend, correlation, and dispersion analyses on EC and EW, as well as their synergistic changes, in the Sanjiang Plain from 1960 to 2019, using inverse distance weighting, statistical methods, and the Mann–Kendall test. The results indicated that cold-to-warm (C2W) and warm-to-cold (W2C) events were significantly and positively correlated with elevation, with correlation coefficients (r) of 0.76 and 0.84, respectively. Meanwhile, C2W showed a significant negative correlation with latitude (r = −0.55), while W2C also exhibited a significant negative correlation with latitude (r = −0.71). However, there was a significant positive correlation between (EC) and latitude (r = 0.65). After 1980, both the declining trend of EC and the increasing trend of EW slowed down, and the trends in C2W and W2C changed from decline to increase. The dispersion of EC and EW shows an increasing trend, while the dispersion of C2W and W2C exhibits a decreasing trend. This study provides important references for studying temperature fluctuations and addressing extreme climate changes.