The North China Plain (NCP) is one of the three great plains in China and also serves as a vital region for grain, cotton, and oil production. Under the influence of regional hydrothermal changes, groundwater overexploitation, and seawater intrusion, the vegetation coverage is undergoing continuous alterations. However, a comprehensive assessment of impacts of precipitation, temperature, and groundwater on vegetation in marine sedimentary regions of the NCP is lacking. Heilonggang Basin (HB) is located in the low-lying plain area in the east of NCP, which is part of the NCP. In this study, the HB was chosen as a typical area of interest. We collected a series of data, including the Normalized Difference Vegetation Index (NDVI), precipitation, temperature, groundwater depth, and Total Dissolved Solids (TDS) from 2001 to 2020. Then the spatiotemporal variation in vegetation was analyzed, and the underlying driving mechanisms of vegetation variation were explored in this paper. The results show that NDVI experiences a rapid increase from 2001 to 2004, followed by stable fluctuations from 2004 to 2020. The vegetation in the HB has achieved an overall improvement in the past two decades, with 76% showing improvement, mainly in the central and eastern areas, and 24% exhibiting deterioration in other areas. From 2001 to 2020, NDVI correlates positively with precipitation, whereas its relationship with temperature fluctuates between positive and negative, and is not statistically significant. There is a threshold for the synergistic change of NDVI and groundwater depth. When the groundwater depth is lower than 3.8 m, NDVI increases sharply with groundwater depth. However, beyond this threshold, NDVI tends to stabilize and fluctuate. In the eastern coastal areas, NDVI exhibits a strong positive correlation with groundwater depth, influenced by the surface soil TDS controlled by groundwater depth. In the central regions, a strong negative correlation is observed, where NDVI is primarily impacted by soil moisture under the control of groundwater. In the west and south, a strong positive correlation exists, with NDVI primarily influenced by the intensity of groundwater exploitation. Thus, precipitation and groundwater are the primary driving forces behind the spatiotemporal variability of vegetation in the HB, while in contrast, the influence of temperature is uncertain. This study has elucidated the mechanism of vegetation response, providing a theoretical basis for mitigating adverse factors affecting vegetation growth and formulating rational water usage regulations in the NCP.

Background: root-zone water transport is crucial in the water transformation from precipitation to groundwater, directly influencing soil moisture distribution and resource acquisition for wetland plants. Methods: This study investigated the movement mechanism of root-zone (0–80 cm) soil water in the Poyang Lake wetland, China, during a dry year. Hydrological observation and stable isotopes (δ¹⁸O and δD) were utilized. Results: The root-zone soil water content was low (2.9–12.6%) at the high site covered by Artemisia capillaris, while it remained high (25.2–30.2%) at the median and low sites covered by Phragmites australis and Carex cinerascens, respectively. The isotopic values of shallow soil water (0–40 cm) in the A. capillaris site followed the seasonal pattern of rainfall isotopes, indicating predominantly rainfall recharge. Rainfall was primarily transported by piston flow, with an infiltration depth of approximately 60 cm. Conversely, depleted water isotopes measured at certain depths in P. australis and C. cinerascens sites closely resembled those of rainfall, suggesting that preferential flow dominated. The average groundwater contribution proportions in root-zone soil water were 65.5% and 57.4% in P. australis and C. cinerascens sites, respectively, while no contribution was detected in A. capillaris site. Conclusions: Preferential flow and groundwater recharge occurred in the P. australis and C. cinerascens sites. They enhance the hydrological connection at the profile scale and are useful for maintaining a favorable root-zone moisture environment for wetland ecosystems in dry years. However, the hydrological connectivity between root-zone soil and groundwater was found to be obstructed in the A. capillaris site. This might be the main reason for vegetation degradation at high elevations in the Poyang Lake wetland.

Revealing the spatiotemporal variation in baseflow and its underlying mechanisms is critical for preserving the health and ecological functions of alpine rivers, but this has rarely been conducted in the source region of the Yangtze River (SRYR). Our study employed the Soil and Water Assessment Tool (SWAT) model coupled with two-parameter digital filtering and geostatistical approaches to obtain a visual representation of the spatiotemporal heterogeneity characteristics of the baseflow and baseflow index (BFI) in the SRYR. The SWAT model and multiple linear regression model (MLR) were used to quantitatively estimate the contribution of climate change and human activities to baseflow and BFI changes. The results underscore the robust applicability of the SWAT model within the SRYR. Temporally, the precipitation, temperature, and baseflow exhibited significant upward trends, and the baseflow and BFI showed contrasting intra-annual distribution patterns, which were unimodal and bimodal distribution, respectively. Spatially, the baseflow increased from northwest to southeast, and from the watershed perspective, the Tongtian River exhibited higher baseflow values compared to other regions of the SRYR. The baseflow and BFI values of the Dangqu River were greater than those of other tributaries. More than 50% of the entire basin had an annual BFI value greater than 0.7, which indicates that baseflow was the major contributor to runoff generation. Moreover, the contributions of climate change and human activities to baseflow variability were 122% and −22%, and to BFI variability, 60% and 40%. Specifically, precipitation contributed 116% and 60% to the baseflow and BFI variations, while the temperature exhibited contributions of 6% and 8%, respectively. Overall, it was concluded that the spatiotemporal distributions of baseflow and the BFI are controlled by various factors, and climate change is the main factor of baseflow variation. Our study offers valuable insights for the management and quantitative assessment of groundwater resources within the SRYR amidst climate change.

The Surface Water and Ocean Topography (SWOT) mission provides reservoir water surface elevation (WSE), but converting absolute WSE to storage remains sensitive to the relative reference and shape of hypsometric curves. Here, we evaluate a site-specific vertical alignment parameter and a hydrostatic-constrained extension for truncated hypsometric curves using 14 reservoirs with concurrent in-situ records and two hypsometric curves: GRDL (Global reservoir dataset through deep learning) and REGEOM (geometric approximation). Under the reference assumption that the maximum observed SWOT WSE corresponds to full capacity, the median capacity-normalized root mean square error (RMSE) is 14.9%. The reservoir-specific full-record calibration reduces this value to 2.9%, showing that effective vertical alignment is a major sensitivity. GRDL yields lower capacity-normalized RMSE than REGEOM. Artificial-truncation experiments show that the constrained extension reproduces withheld portions of tabulated curves with median reconstruction errors below 1% across the tested distances. A chronological 60/40 holdout test supports temporal generalization after local calibration: for the 11 reservoirs, the median capacity-normalized RMSE is 0.026 in both calibration and validation periods. In contrast, leave-one-reservoir-out tests find no statistically significant improvement over the reference assumption. The results therefore support locally calibrated, sampled storage retrieval while showing that transfer of a single alignment parameter to fully ungauged reservoirs remains unresolved.