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Partitioning of evapotranspiration (ET) into soil evaporation (E) and plant transpiration (T) poses a significant challenge. This study proposed a novel approach that combines eddy covariance, micro-lysimeter, and high-resolution unmanned aerial vehicle (UAV) images within the flux footprint to optimize the canopy and soil resistances of the Shuttleworth-Wallace model (S-W) using a multi-objective optimization scheme. A two-year experiment was conducted at the Yucheng and Luancheng sites to investigate the effectiveness of the proposed method for the summer maize-wheat winter system in the North China Plain. Our results showed that the S-W model with multi-objective optimization by using high-resolution UAV images within the flux footprint significantly improved the estimation accuracy of ET components compared with the traditional one- and two-objective optimization schemes. The estimation of ET, T, and E of our method had an average root mean square error of 0.67 mm day−1, 0.66 mm day−1, and 0.28 mm day−1, respectively. The optimized S-W model using high-resolution UAV data within the flux footprint produced better ET partitioning than that optimized using Moderate Resolution Imaging Spectroradiometer (MODIS) data. We then applied the proposed method to estimate ET and ET components in the North China Plain. This study highlighted the importance of utilizing multi-source data (especially high-resolution UAV images) and multi-objective optimization for accurate ET partitioning.

The overexploitation of groundwater and the excessive application of nitrogen (N) fertilizer under the intensive double cropping system are responsible for the groundwater level decline and potential contamination in the North China Plain (NCP). Alternative cropping systems have the potential to alleviate current groundwater and N problems in the region, while there are limited studies simultaneously focusing on the impact of a change of cropping systems on crop yields, groundwater consumption, and N leaching. In this study, Field observed experiments of double-cropping system (i.e., winter wheat–summer maize) and mono-cropping system (early sowing maize) were used to calibrate and validate the Root Zone Water Quality Model (RZWQM2). Then, the validated RZWQM2 model was used to evaluate the long-term crop growth and environmental impact under the local winter wheat–summer maize rotation system with practical irrigation (WW-SM_pi) and auto-irrigation (WW-SM_ai), and three alternative cropping systems (single early maize, SEM; winter wheat–summer maize and single early maize, WW-SM-SEM; winter wheat-summer maize and double single early maize, WW-SM-2SEM). The net consumption of groundwater and N leaching under WW-SM_pi were 226.9 mm yr−1 and 79.7 kg ha−1 yr−1, respectively. Under the local rotation system, auto-irrigation could increase crop yields and N leaching. Compared with the WW-SM_ai, the alternative cropping systems, WW-SM-SEM, WW-SM-2SEM, and SEM, significantly decreased the net consumption of groundwater by 49.3%, 63.0%, and 97.8%, respectively (147.5–292.9 mm), and N leaching by 53.5%, 67.5%, and 89.6%, respectively (50.0–83.7 kg ha−1). However, the yields of the three alternative cropping systems were reduced by less than 30% (12.2%, 20.1%, and 29.7%, respectively). The simulated results indicated that appropriately decreasing the planting frequency of winter wheat is an effective approach to reduce groundwater overexploitation and N contamination with a relatively limited reduction in grain yields. The results could provide a scientific basis for cropping system adjustment in guaranteeing sustainable regional water and grain policy.

The Huang-Huai-Hai (3H) Plain is the major crop-producing region in China. Due to the long-term overexploitation of groundwater for irrigation, the groundwater funnel is constantly expanding and the scarcity of water resources is prominent in this region. In this study, Gravity Recovery and Climate Experiment (GRACE) and hydrological models were used to estimate the spatial-temporal changes of groundwater storage (GWS) and the driving factors of GWS variations were discussed in the 3H Plain. The results showed that GRACE-based GWS was depleted at a rate of −1.14 ± 0.89 cm/y in the 3H Plain during 2003 to 2015. The maximum negative anomaly occurred in spring due to agricultural irrigation activities. Spatially, the loss of GWS in the Haihe River Basin is more serious than that in the Huaihe River Basin, presenting a decreasing trend from south to north. Conversely, the blue water footprint (WFblue) of wheat exhibited an increasing trend from south to north. During the drought years of 2006, 2013, and 2014, more groundwater was extracted to offset the surface water shortage, leading to an accelerated decline in GWS. This study demonstrated that GWS depletion in the 3H Plain is well explained by reduced precipitation and groundwater abstraction due to anthropogenic irrigation activities.

The Luancheng Agro-Ecosystem Experimental Station, the Chinese Academy of Sciences, is located in the piedmont plain area of North China Plain and the middle section of the Taihang Mountain alluvial plain. It is a typical representative of the high-yield agricultural eco-system in the groundwater irrigation area. Due to the large-scale and high-intensity agricultural production in recent decades, the regional groundwater has been seriously over exploited, and the risk of groundwater pollution has increased. However, the surface agro-ecosystem and aquifer are separated by thick vadose zones, hence the mechanism of the impact of surface agricultural activities on the quantity and quality of groundwater is still unclear. The in-situ monitoring throughout the entire vadose zone is the only method to reveal the mechanism of this process. Therefore, the establishment of a large-scale critical zone observatory is the most important requisite for conducting research on the relationship between agriculture and groundwater. With the support of the cornerstone research infrastructure project for the field station network of the Chinese Academy of Sciences, Luancheng Station began to construct the "Water and Solute Cycle Observation Platform in Groundwater-Soil-Crop System" in 2016, and the construction was completed in November 2020. An observatory caisson with a depth of 48 m and an inner diameter of 2.8 m has been built. The platform was officially named 'Luancheng Critical Zone Observatory' (LC-CZO). LC-CZO can measure the key variables such as soil water content, matric potential, soil temperature, and solute concentration in the root zone-deep vadose zone-saturated zone. The monitoring results enable the study on the patterns of the transport and transformation of water, solutes and pollutants in the thick vadose zone reveal the hydrological process of the saturated-unsaturated transition zone and its relationship with groundwater replenishment, explain the migration and transformation of nitrogen applied in farmland and its impact on groundwater quality, and provide experimental platform support for exploring the impact mechanism of land surface process on the groundwater quantity and quality. [ABSTRACT FROM AUTHOR]

The north-south trending basin of Ejina in Inner Mongolia of northernwestern China, Central Asia is located at the lower reaches of the Heihe River watersheds and is a regional tectonic depression limited to the west part of the Alashan Plateau. Though neotectonic activity is believed to be the major factor in the evolution of the topography, detailed documentation and analysis of climatic landscape features like alluvial fans, desert plains, aeolian dunes and bedrock gorges and their environmental implications are lacking. The present study is a site-specific documentation of landforms developed in the wide part of the Ejina Basin, with the aim to identify the climatic landforms based on the method of climatic geomorphology and to evaluate its landscape evolution and response to palaeoclimate changes. The morphodynamics of older landscapes are recognized by making comparison with the present climate and its corresponding landscapes. Occurrence of desert plains and aeolian dunes in the central basin is inferred to be the products of modern hyper-arid climate. No active geomorphoclimatic dynamics for development of desert bedrock gorges and pediments is observed at the margins in the present day conditions, thus we infer an obvious linkage of these landforms to the humid phases, which provided high energy runoff for the formation of landforms associated erosional features. Clear evidences testifying the basin-scale shifting and transformation of different morphoclimatic zones in the Ejina basin are observed, which prove that the main geomorphic unit is changed from an alluvial-lacustrine plain to a desert plain. Pediments and desert gorges are both relict landforms associated with more humid and colder climate during the last glacial period. However, the coexistence of diverse landscapes and the consequent geomorphodiversity in the basin should be a compound result of surficial processes other than glaciations. Fluvial/alluvial actions, aeolian, abrasion/deflation, aggradation and degradation processes together with climatic changes have conjunctionally played important role. The climate and hydrological conditions of the basin during the last glaciation and during the Early Holocene were much better than at present, possibly having an average annual precipitation ranged between 60~350 mm on the margins of the basin and being characterized in the central basin by high lake levels during ca. 39-23 ka BP but great fluctuations during Holocene. Because the Asian summer monsoon was quite weak during the glacial times, the periods of lower aridity during the late Pleistocene in the Ejina Bain could be induced by an increase of the westerlies and a weakening of the Asian winter monsoon on the arid areas of the central Asia. [ABSTRACT FROM AUTHOR]

The impacts of environmental flow controls on the water table and chemistry of groundwater in the Ejina Delta, an arid inland river basin in northwest China, were investigated with field observations in 2001 and 2009. The results indicate that the shallow groundwater level rose by 0-2 m in the upper reaches of the east tributary of the Heihe River and in the areas of Saihantaolai-Dalaikubu during the period of environmental flow controls. The chemical constituents of the groundwater show a distinct spatial heterogeneity with the total dissolved solids (TDS) in the groundwater increasing from the periphery towards the depocenter of the Ejina Basin. In addition, the rate of groundwater cycling in the south of the Ejina Delta increased, and the mineralization of groundwater declined, while the overall mineralization and salinity increased in the northern regions, especially in the depocenter of the Ejina Basin. Since shallow groundwater is important to the ecology of arid regions, and because understanding the changes in the shallow groundwater environment (groundwater level and hydrochemistry) in response to environmental flow controls is essential for the sustainable improvement of the ecological environment, the results of this paper can be used as a reference for watershed water resources planning and management to help maintain the health and proper function of rivers in arid regions. [ABSTRACT FROM AUTHOR]