Correlation Analysis Between Groundwater Decline Trend and Human-Induced Factors in Bashang Region

Revegetation projects significantly improved ecosystem service values in the agro-pastoral ecotone of northern China in recent 20 years

Revegetation is a conventional approach used for ecological protection and restoration projects, especially in the agro-pastoral ecotone of northern China (AENC). However, for this ecologically vulnerable area, the changes in land use and ecosystem service values (ESV) resulting from revegetation projects have received little attention and have not been fully elucidated. In this study, based on a rapid valuation tool-the benefit transfer method modified by the biomass factor (net primary productivity, NPP)-we assessed the ESV of the AENC at multiple-time scales by designing land scenarios related to local revegetation projects. The results showed that forestland expansion (+697 thousand ha) and grassland shrinkage (-650 thousand ha) dominated the land use change in the AENC in 2000-2018 and indirectly resulted in a net increase of US$8.18 billion in total ESV, in which revegetation projects generated nearly 1.5 million ha of new vegetated land and a corresponding US$6.86 billion in ESV (83.83% of the total increase). For future revegetation, the returning-farmland-to-forestland scenario exhibited a greater potential with increases of 5.66 million ha of forestland and US$65.20 billion in ESV to be provided. Overall, revegetation projects improved the ESV of the AENC in the last two decades because of the pronounced expansion in forestland of high ESV at the expense of the reductions in farmland and grassland, and this trend will be led continually by the Grain for Green Project in the future through the rapid assessment based on the modified benefit transfer method. Specifically, more investments and attention must be directed to the protection and restoration of grassland and wetland ecosystems.

Monitoring Terrestrial Water Storage Changes with the Tongji-Grace2018 Model in the Nine Major River Basins of the Chinese Mainland

Data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission can be used to monitor changes in terrestrial water storage (TWS). In this study, we exploit the TWS observations from a new temporal gravity field model, Tongji-Grace2018, which was developed using an optimized short-arc approach at Tongji University. We analyzed the changes in the TWS and groundwater storage (GWS) in each of the nine major river basins of the Chinese mainland from April 2002 to August 2016, using Tongji-Grace2018, the Global Land Data Assimilation System (GLDAS) hydrological model, in situ observations, and additional auxiliary data (such as precipitation and temperature). Our results indicate that the TWS of the Songliao, Yangtze, Pearl, and Southeastern River Basins are all increasing, with the most drastic TWS growth occurring in the Southeastern River Basin. The TWS of the Yellow, Haihe, Huaihe, and Southwestern River Basins are all decreasing, with the most drastic TWS loss occurring in the Haihe River Basin. The Continental River Basin TWS has remained largely unchanged over time. With the exception of the Songliao and Pearl River Basins, the GWS results produced by the Tongji-Grace2018 model are consistent with the in situ observations of these basins. The correlation coefficients for the Tongji-Grace2018 model results and the in situ observations for the Yellow, Huaihe, Yangtze, Southwestern, and Continental River Basins are higher than 0.710. Overall, the GWS results for the Songliao, Yellow, Haihe, Huaihe, Southwestern, and Continental River Basins all exhibit a downward trend, with the most severe groundwater loss occurring in the Haihe and Huaihe River Basins. However, the Yangtze and Southeastern River Basins both have upward-trending modeled and measured GWS values. This study demonstrates the effectiveness of the Tongji-Grace2018 model for the reliable estimation of TWS and GWS changes on the Chinese mainland, and may contribute to the management of available water resources.

The Impact of Land Use Change on Water-Related Ecosystem Services in the Bashang Area of Hebei Province, China

Land use change is an important scientific issue recognized for its potential to alter ecosystem services (ESs), especially water-related ecosystem services (WRESs). Using the integrated valuation of ecosystem services and trade-offs (InVEST) model, this study quantified and mapped spatiotemporal variations in land use and corresponding WRESs in the Bashang area of Hebei Province, China (BAHP) to investigate how land use change impacted WRESs by means of scenario analysis, especially, in which a new evaluation indicator, average ecology effect (AEE) was proposed and well applied. The results indicated that woodland expansion (+602.61 km2) and grassland shrinkage (−500.57 km2) dominated the land use change in the BAHP in 2000–2018, which altered local WRESs, including the moderate declines in water purification and water yield, as well as a significant enhancement in soil conservation. In scenario analysis, compared to baseline levels, riparian woodland buffer and planting trees scenarios slightly decreased water yield but strengthened water purification and soil conservation; reclaiming wasteland and integrated development scenarios significantly enhanced soil conservation but lowered water yield and water purification; fertilizer reduction scenario effectively mitigated water deterioration. According to AEE, the riparian woodland buffer (RWB) scenario performed greater than the planting trees (PT) scenario on variations of WRESs per unit area, which differed completely from the results based on total variations. Overall, a multiple-scale indicator for a comprehensive evaluation of ESs should receive more attention.

Divergent Trends of Water Storage Observed via Gravity Satellite across Distinct Areas in China

Knowledge of the spatiotemporal variations of terrestrial water storage (TWS) is critical for the sustainable management of water resources in China. However, this knowledge has not been quantified and compared for the different climate types and underlying surface characteristics. Here, we present observational evidence for the spatiotemporal dynamics of water storage based on the products from the Gravity Recovery and Climate Experiment (GRACE) and the Global Land Data Assimilation System (GLDAS) in China over 2003–2016. Our results were the following: (1) gravity satellite dataset showed divergent trends of TWS across distinct areas due to human factors and climate factors. The overall changing trend of water storage is that the north experiences a loss of water and the south gains in water, which aggravates the uneven spatial distribution of water resources in China. (2) In the eastern monsoon area, the depletion of water storage in North China (NC) was found to be mostly due to anthropogenic disturbance through groundwater pumping in plain areas. However, precipitation was shown to be a key driver for the increase of water storage in South China (SC). Increasing precipitation in SC was linked to atmospheric circulation enhancement and Pacific Ocean warming, meaning an unrecognized teleconnection between circulation anomalies and water storage. (3) At high altitudes in the west, the change of water storage was affected by the melting of ice and snow due to the rising temperatures, yet the topography determines the trend of water storage. We found that the mountainous terrain led to the loss of water storage in Tianshan Mountain (TSM), while the closed basin topography gathered the melted water in the interior of the Tibetan Plateau (ITP). This study highlights the impacts of the local climate and topography on terrestrial water storage, and has reference value for the government and the public to address the crisis of water resources in China.

Effects of Urbanization on Watershed Evapotranspiration and Its Components in Southern China

Understanding the effects of land use change on evapotranspiration (ET) and its partitioning to transpiration and evaporation is important for accurately evaluating the likely environmental impacts on watershed water supply, climate moderation, and other ecosystem services (e.g., carbon sequestration and biodiversity). This study used a distributed hydrologic model, MIKE SHE, to partition evapotranspiration into soil evaporation, transpiration, ponded water evaporation, and interception, and examined how the ET partitions affected the water balance in the Qinhuai River Basin from 2000 to 2013. Simulated daily ET was compared to measurements at an eddy flux research site during 2016–2017 (R2 = 0.72). Degradation in rice-wheat rotation fields and expansion of impervious surfaces impacted not only total watershed evapotranspiration, which showed a significant downward trend (p < 0.05), but also its partitioning. A significant (p < 0.01) decrease in transpiration was detected. Ponded water evaporation was the only ET partition that exhibited a significant positive trend (p < 0.05). We concluded that the reduced transpiration as a result of land use and land cover change was the primary factor driving the variation of watershed scale evapotranspiration. In addition, there was an increase in annual water yield (23%) as a response to significant reduction in ET (7%) due to a 175% expansion of urban area in the study watershed. Our study provided insights to the mechanisms of land surface–water cycle interaction and better understanding of the effects of land use change on urban micro-climate such as “urban dry island” and “urban heat island” effects.

Detecting Winter Wheat Irrigation Signals Using SMAP Gridded Soil Moisture Data

The southern part of the Hebei Province is one of China’s major crop-producing regions. Due to the continuous decline in groundwater level, agricultural water use is facing significant challenges. Precision agricultural irrigation management is undoubtedly an effective way to solve this problem. Based on multisource data (time series soil moisture active passive (SMAP) data, Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and evapotranspiration (ET), and meteorological station precipitation), the irrigation signal (frequency, timing and area) is detected in the southern part of the Hebei Province. The SMAP data was processed by the 5-point moving average method to reduce the error caused by the uncertainty of the microwave data derived SM. Irrigation signals can be detected by removing the precipitation effect and setting the SM change threshold. Based on the validation results, the overall accuracy of the irrigation signal detection is 77.08%. Simultaneously, considering the spatial resolution limitation of SMAP pixels, the SMAP irrigation area was downscaled using the winter wheat area extracted from MODIS NDVI. The analytical results of 55 winter wheat samples (5 samples in a group) showed that winter wheat covered by one SMAP pixel had an 82.72% growth consistency in surface water irrigation period, which can indicate a downscaling effectiveness. According to the above statistical analysis, this paper considers that although the spatial resolution of SMAP data is insufficient, it can reflect the change of SM more sensitively. In areas where the crop pattern is relatively uniform, the introduction of high-resolution crop pattern distribution can be used not only to detect irrigation signals but also to validate the effectiveness of irrigation signal detection by analyzing crop growth consistency. Therefore, the downscaling results can indicate the true winter wheat irrigation timing, area and frequency in the study area.