Search

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: Shallow groundwater plays a key role in agro‐hydrological processes of arid areas. Groundwater often supplies a necessary part of the water requirement of crops and surrounding native vegetation, such as groundwater‐dependent ecosystems. However, the impact of water‐saving irrigation on cropland water balance, such as the contribution of shallow groundwater to field evapotranspiration, requires further investigation. Increased understanding of quantitative evaluation of field‐scale water productivity under different irrigation methods aids policy and decision‐making. In this study, high‐resolution water table depth and soil water content in field maize were monitored under conditions of flood irrigation (FI) and drip irrigation (DI), respectively. Groundwater evapotranspiration (ETg) was estimated by the combination of the water table fluctuation method and an empirical groundwater–soil–atmosphere continuum model. The results indicate that daily ETg at different growth stages varies under the two irrigation methods. Between two consecutive irrigation events of the FI site, daily ETg rate increases from zero to greater than that of the DI site. Maize under DI steadily consumes more groundwater than FI, accounting for 16.4% and 14.5% of ETa, respectively. Overall, FI recharges groundwater, whereas DI extracts water from shallow groundwater. The yield under DI increases compared with that under FI, with less ETa (526 mm) compared with FI (578 mm), and irrigation water productivity improves from 3.51 kg m−3 (FI) to 4.58 kg m−3 (DI) through reducing deep drainage and soil evaporation by DI. These results highlight the critical role of irrigation method and groundwater on crop water consumption and productivity. This study provides important information to aid the development of agricultural irrigation schemes in arid areas with shallow groundwater. [ABSTRACT FROM AUTHOR]

Improving the efficiency of water consumption and water productivity is the key approach to satisfy sustainable water resource supply and food demand. As effective measures, water saving practices are implemented in arid and semi-arid regions. For areas with shallow groundwater, water used for irrigation is not entirely consumptively used. The majority of irrigation water infiltrations below the root zone are stored in shallow groundwater. This can be reused as groundwater based evapotranspiration (ET g ) at the regional scale. Thus, actual regional efficiency of water consumption (REWC) based on all water within the hydrological system is greater than based on consumptive use only. Accurately evaluating the response of REWC and regional water productivity (RWP) to water saving practices is essential due to the complexity of the hydrological system. In this study, regional ET g and regional evapotranspiration (ET) of the past 20 years were reproduced in a typical arid irrigation district with shallow groundwater based on the water balance method. Furthermore, REWC and RWP were estimated to investigate the impact of water saving practices to regional water use. Simulation results show that groundwater is a significant water source of regional ET in arid regions with a shallow aquifer and contributes more than 16% of regional ET for the irrigation district. Water saving practice implementation enhances the contribution of groundwater to ET. After water saving practices implementation, annual REWC and RWP have been improved by 0.07 and 0.1 kg/m 3 , respectively. Furthermore, negative correlation between REWC and I + P (the total water supply including rainfall and irrigation water diversion) and positive correlation between RWP and REWC demonstrate that water saving practices can reduce the non-beneficial water losses by evaporation and enhance productivity by a lower groundwater table. Overall, shallow groundwater plays an important role to enhance REWC and RWP and the contribution of groundwater to regional water use needs to be considered as part of a reasonable water saving strategy towards a sustainable agricultural system. [ABSTRACT FROM AUTHOR]

The Gravity Recovery and Climate Experiment (GRACE) has been in operation since 2002. Water storage estimates are calculated from gravity anomalies detected by the operating satellites and although not the true resolution, can be presented as 100 km × 100 km data cells if appropriate scaling functions are applied. Estimating total water storage has shown to be highly useful in detecting hydrological variations and trends. However, a limitation is that GRACE does not provide information as to where the water is stored in the vertical profile. We aim to partition the total water storage from GRACE into water storage components. We use a wavelet filter to decompose the GRACE data and partition it into various water storage components including soil water and groundwater. Storage components from the Australian Water Resources Assessment (AWRA) model are used as a reference for the decompositions of total storage data across Australia. Results show a clear improvement in using decomposed GRACE data instead of raw GRACE data when compared against total water storage outputs from the AWRA model. The method has potential to improve GRACE applications including a means to test various large scale hydrological models as well as helping to analyse floods, droughts and other hydrological conditions. [ABSTRACT FROM AUTHOR]

Groundwater strongly impacts ecosystem performance in arid regions by driving vegetation structure and species distribution. It is unknown how water use efficiency varies along a gradient of depth to groundwater ( DWT ). In this study, we developed a framework to estimate water use efficiency ( WUE ), groundwater use efficiency ( GUE ), and rain use efficiency ( RUE ), and to examine the contribution of rainfall to transpiration in groundwater-dependent ecosystems (GDEs). The method was applied to an arid region in northwest China with a gradient of groundwater depth from 0.5 to 12 m. The results indicate that the above-ground primary production, evapotranspiration, plant transpiration, WUE , and GUE decreased significantly from riparian forest, wetland, oasis edge, desert-oasis ecotone, and to sandy desert along a gradient of increasing DWT . RUE is found to be 0.26 g m −2 mm −1 at the sandy desert without groundwater contribution where 21% of rainfall is used for transpiration. Water use efficiency increases to 0.85 g m −2 mm −1 at the riparian site where groundwater is about 0.5 m depth. The fraction of rainfall consumed by plants increases with a decreasing DWT from a threshold of 6.3 m, suggesting groundwater enhances rain use efficiency in GDEs. [ABSTRACT FROM AUTHOR]

Highlights: [•] We investigated water budget over Australia based on three satellite products. [•] Data are more consistent at seasonal and annual scales than monthly in central WA. [•] Products’ integrated error in Lake Eyre Basin (LEB) is smaller than 6.2mm/year. [•] Maximum net groundwater inflow to LEB is 6.2mm/year. [•] Australian total runoff to the oceans is estimated to be 144.7±11.3mm/year. [ABSTRACT FROM AUTHOR]

The article presents a study which investigated the effects of root distribution on deep percolation into the underlying permeable bedrock for a given soil profile and climate condition with the use of HYDRUS modelling at a semiarid ponderosa pine hillslope. Results of the sensitivity analysis show that the root macropore effect dominates saturated soil water flow in low conductivity soils. It was found that potential groundwater recharge is impeded by the clay-rich soil layer without root-induced macropores.

• Maize sap flow was measured in two fields with contrasting water table depths. • The influencing environmental factors were examined at sub-daily and daily scales. • Transpiration and water productivity under two groundwater depths were evaluated. • The optimum groundwater depth for maize was determined by high water productivity. A better understanding of crop transpiration and its influencing factors in arid areas where irrigation is required contributes to improving agricultural water productivity and water resources management. However, previous studies from different regions have not come to a consensus on which factors and how they control crop transpiration, and little is known for areas with a shallow groundwater table. In this study, maize (Zea mays L.) transpiration was investigated under two groundwater table depths (WTDs) during two growing seasons. Sap velocity (SV), micrometeorological conditions and water regimes were monitored to evaluate transpiration rates under different WTDs and their relationships to environmental and hydrologic conditions. Results show that the combination of photosynthetic active radiation (PAR) and vapor pressure deficit (VPD) mainly controlled the diurnal dynamics of SV. PAR better explained the temporal variability of transpiration than solar radiation at hourly scale. At daily scale, the two-segment transpiration response to VPD was observed, suggesting that the studied species likely has a capacity of drought-tolerance. On average, SV was found to be larger during midday for the shallower WTD in 2016 than the deeper one. For different seasons, the shallower WTD in 2017 also led to larger transpiration than the deeper one in 2016. Given similar yields for all cases, the maize field with the deeper WTD in 2016 was estimated to have higher water productivity. An optimum water use efficiency WTD was determined by assessing the normalized transpiration difference with the varying WTD and it was about 2.1–2.2 m for maize in this area. These results shed light on the most effective utilization of the valuable water confronting the changing climate in arid areas with shallow groundwater. [ABSTRACT FROM AUTHOR]

• J s was modified considering sapwood width and insertion direction. • Groundwater table rise due to canal infiltration increased J s by 5.5–25.8% • Impact of ET o and groundwater on J s was quantified. • The threshold of groundwater table depth to support J s is about 3.6 m. Shelterbelts play an important ecological function in arid irrigation land, while competing for water which otherwise supports crop growth. Estimation of shelterbelt water consumption from groundwater is essential to better manage shelterbelts in irrigation districts, but often a challenging task due to its geometry and varying accessibility to groundwater. In the study, sap flow of Populus popularis planted along an irrigation canal was measured during two growing seasons (2016–2017) to investigate its response to varying shallow groundwater. Considering the radial pattern of sap flux density (J s) and measurement azimuthal effect, corrected J s was adopted to better represent transpiration. The results indicate that increased soil moisture and groundwater table during irrigation periods with water flowing in the canal enhance relative J s of shelterbelt by 5.5–25.8% from the non-irrigation intervals. The threshold of groundwater depth (3.6 m) is identified, beyond which transpiration of the seven-year-old shelterbelt becomes very low. Greenbelt transpiration strongly depends on groundwater within the threshold, and can be estimated through an exponential function of the ratio of atmospheric demand and groundwater depth. Besides, with the decrease of reference evapotranspiration from June to September, the sensitivity of shelterbelt transpiration response to groundwater table depth was increased. This study provides necessary information to evaluate farmland shelterbelt transpiration for rational water resource allocation to meet the ecological water requirement in arid areas with shallow groundwater. [ABSTRACT FROM AUTHOR]