Soil Evaporation Research Articles

An Unexpected Decline in Spring Atmospheric Humidity in the Interior Southwestern United States and Implications for Forest Fires

Abstract On seasonal time scales, vapor pressure deficit (VPD) is a known predictor of burned area in the southwestern United States (“the Southwest”). VPD increases with atmospheric warming due to the exponential relationship between temperature and saturation vapor pressure. Another control on VPD is specific humidity, such that increases in specific humidity can counteract temperature-driven increases in VPD. Unexpectedly, despite the increased capacity of a warmer atmosphere to hold water vapor, near-surface specific humidity decreased from 1970 to 2019 in much of the Southwest, particularly in spring, summer, and fall. Here, we identify declining near-surface humidity from 1970 to 2019 in the southwestern United States with both reanalysis and in situ station data. Focusing on the interior Southwest in the months preceding the summer forest fire season, we explain the decline in terms of changes in atmospheric circulation and moisture fluxes between the surface and the atmosphere. We find that an early spring decline in precipitation in the interior region induced a decline in soil moisture and evapotranspiration, drying the lower troposphere in summer. This prior season precipitation decline is in turn related to a trend toward a Northern Hemisphere stationary wave pattern. Finally, using fixed humidity scenarios and the observed exponential relationship between VPD and burned forest area, we estimate that with no increase in temperature at all, the humidity decline alone would still lead to nearly one-quarter of the observed VPD-induced increase in burned area over 1984–2019. Significance Statement Burned forest area has increased significantly in the southwestern United States in recent decades, driven in part by an increase in atmospheric aridity [vapor pressure deficit (VPD)]. Increases in VPD can be caused by a combination of increasing temperature and decreasing specific humidity. As the atmosphere warms with climate change, its capacity to hold moisture increases. Despite this, there is a decrease in near-surface air humidity in the interior southwestern United States over 1970–2019, which during the summer is likely caused by a decline in early spring precipitation leading to limited soil moisture and evaporation in spring and summer. We estimate that this declining humidity alone, without an increase in temperature, would cause about one-quarter of the VPD-induced increase in burned forest area in this region over 1984–2019.

Performance of Some Organic Mulch Materials for Weed Suppression, Soil Conditions and Yield in Capsicum annuum L. Cultivation

The aim of this study was to investigate the effectiveness of different organic mulch materials and thicknesses in controlling weeds, improving soil temperature and moisture, and increasing crop yield in Capsicum annuum L. cultivation. The experiment was conducted in 2022, using three types of mulch materials (grass, chopped paper, wheat straw) and three different thicknesses (5 cm, 10 cm, 15 cm). A total of 22 weed species were identified in the experimental area, and statistical analysis revealed significant differences in all parameters between the mulch treatments and the control group. The use of organic mulch resulted in better weed control, with an increase in mulch thickness corresponding to greater suppression of annual weed species. The highest effect on weed dry weight was observed in the 15-cm paper mulch, which also produced the highest yield (3940.48 kg/da). The study also showed that soil temperature was lower and soil moisture was higher in all mulch treatments compared to the bare soil control group, with some fluctuations observed at times. Overall, the findings suggest that the use of organic mulch is crucial in arid and semi-arid regions for effective weed control, water conservation, improved water efficiency, reduced soil evaporation, and increased pepper yield.

NON-ISOTHERMAL MODELING OF SOIL VAPOR EXTRACTION SYSTEM INCLUDING SOIL TEMPERATURE EFFECT

Soil vapor extraction (SVE) is a proven effective in-situ technology for the removal of volatileorganic compounds (VOCs) from the subsurface. SVE process is highly sensitive to temperature.Studying annual soil temperature variation with depth declares that there is a considerable temperaturevariation in the upper few meters that may affect the overall efficiency of SVE process.A numerical model was developed to aid in investigation of field-scale soil vapor extractionprocess. The model is three-dimensional, time dependent that simulates nonisothermal vapor flow andtransport of multicomponent mixtures in soil and keeps track of the distribution of each compound inthe other three immobile phases (NAPL, aqueous, and sorbed). Rate limited interphase mass transferwith linear driving force expressions were used to model volatilization of oil into gas phase. A localequilibrium partitioning was assumed between gas, water, and solid phase. The model equations werediscretized using a standard Galerkin finite element method and solved using set iterative solutionalgorithm.Simulation of hypothetical field-scale problems was done. The physical domain described a threedimensionalsystem with flow to a single extraction well. A hypothetical soil temperature variationwith depth was incorporated with the model. The result of these simulations showed that thistemperature variation has a considerable effect on system efficiency and may play a role in optimumsystem configuration.

Evapotranspiration partitioning by integrating eddy covariance, micro-lysimeter and unmanned aerial vehicle observations: A case study in the North China Plain

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 use of green infrastructure and irrigation in the mitigation of urban heat in a desert city

Severe urban heat, a prevalent climate change consequence, endangers city residents globally. Vegetation-based mitigation strategies are commonly employed to address this issue. However, the Middle East and North Africa are under investigated in terms of heat mitigation, despite being one of the regions most vulnerable to climate change. This study assesses the feasibility and climatic implications of wide-scale implementation of green infrastructure (GI) for heat mitigation in Riyadh, Saudi Arabia—a representative desert city characterized by low vegetation coverage, severe summer heat, and drought. Weather research forecasting model (WRF) is used to simulate GI cooling measures in Riyadh’s summer condition, including measures of increasing vegetation coverage up to 60%, considering irrigation and vegetation types (tall/short). In Riyadh, without irrigation, increasing GI fails to cool the city and can even lead to warming (0.1 to 0.3 °C). Despite irrigation, Riyadh’s overall GI cooling effect is 50% lower than GI cooling expectations based on literature meta-analyses, in terms of average peak hour temperature reduction. The study highlights that increased irrigation substantially raises the rate of direct soil evaporation, reducing the proportion of irrigation water used for transpiration and thus diminishing efficiency. Concurrently, water resource management must be tailored to these specific considerations.

Research Needs Regarding the Vapor Intrusion Potential of Volatile Per- and Polyfluoroalkyl Substances.

Certain per- or polyfluoroalkyl substances [e.g., fluorotelomer alcohols (FtOHs), perfluorooctane sulfonamides (FOSAs), and perfluorooctane sulfonamidoethanols (FOSEs)] have sufficient volatility to merit investigation of the vapor intrusion pathway on a site-specific basis, when they occur as subsurface contaminants in sufficient concentrations near occupied buildings. This perspective summarizes some of the evidence that these categories of per- or polyfluoroalkyl substances are volatile and offers specific research questions and objectives, for purposes of further assessing whether FtOHs, FOSAs, and/or FOSEs can pose indoor exposures via soil vapor intrusion and under what circumstances.

Water Uptake Characteristics of Stipa bungeana Trin: Affected by Subsidence in the Coal Mining Areas of Northwest China

Revealing the water use pattern of plants influenced by coal-mining-caused land subsidence is crucial to understand plant–water interactions and guide ecological restoration. However, available information on herbaceous plants, the dominant species in most arid and semi-arid regions with abundant coal resources, remains inadequate. We investigated the water use patterns of Stipa bungeana Trin. by measuring soil water content, root distribution, and stable isotopes of hydrogen (δ2H) and oxygen (δ18O) of soil water and plant stem water both before and after a rainfall event. The results revealed that prior to rainfall, both areas exhibited a low soil water content with no discernible difference in soil drought. However, the soil waters δ2H and δ18O were found to be more enriched at varying depths within the subsidence area, indicating a heightened level of soil evaporation. Both soil water content and soil water isotopic composition responded sensitively to rainfall, with rainfall primarily replenishing the shallow layer (0–20 cm), thereby reflecting an infiltration mode dominated by piston flow. More water seeped into deeper soil layers in the subsidence area compared to the non-subsidence area, with more preferential flow. Before rainfall, the sources of plant water uptake were consistent both at shallow and deep soil layers, implying that the proportion of water uptake gradually decreased with increasing depth. After rainfall, the sources of plant water uptake differed slightly between the two soil layers. The plants in non-subsidence and subsidence areas dominantly extracted soil water at depths greater than 10 cm and 20 cm, respectively. The root system in the subsidence area was more developed than that in the non-subsidence area. Plant water uptake was primarily influenced by the spatial distribution of roots, as well as the post-rainfall water distribution, regardless of whether they were in the subsidence area or not. Although land subsidence affected soil water transport, the water uptake pattern of Stipa bungeana Trin. was similar before and after rainfall, indicating the adaptive growth of plants through their roots in the subsidence area. The high adaptability of herbs such as Stipa bungeana Trin. makes them a viable option for vegetation restoration in subsidence areas. This study has significant implications for evaluating plant–water relationships in subsidence areas due to coal mining, thereby providing a fundamental basis and valuable reference for ecological restoration and management strategies within such affected regions.

Nature-inspired optimal tuning of input membership functions of fuzzy inference system for groundwater level prediction

We present a novel regression algorithm that combines a Fuzzy Inference System (FIS) with a nature-inspired algorithm to predict variations in GroundWater Levels (GWLs). Initially, we considered several input features, including precipitation, temperature, evaporation, relative humidity, soil type, and GWL Lag. A feature importance analysis using regression tree ensemble learning reveals GWL lag as the most relevant feature and soil type as the least relevant. We eliminate features with low importance scores (soil type, temperature, and evaporation) to improve the computational efficiency. Our approach leverages Fuzzy C-Means (FCM) clustering to develop a Sugeno-type FIS with definite clusters. The dataset is clustered based on feature similarity, and Gaussian membership functions are assigned to each cluster. The mapping of each point is controlled by the range and standard deviation of the Gaussian membership functions. We train the model keeping 70% of the dataset, iteratively tuning the parameters of the Gaussian membership function for all clusters through the Invasive Weed Optimization (IWO) algorithm. The performance of the model is then evaluated using the remaining 30% of the datasets. The F-IWO-GWL model accurately predicts GWL fluctuations, achieving a high correlation coefficient (R = 0.89), low normalized root mean square error (nRMSE = 0.18), and minimal bias (bias = 0.08). A comparative analysis involving seventeen benchmark algorithms reveals the superior performance of our algorithm. To ensure a fair comparison, we calculated key metrics including Akaike’s Information Criterion (AIC), Bayesian Information Criterion (BIC), and Corrected AIC (AICc). The F-IWO-GWL algorithm exhibits the lowest values for AIC, BIC, and AICc among all tested algorithms, suggesting the best goodness-of-fit. This study provides a robust approach for predicting GWL fluctuation, applicable to various groundwater management scenarios. It offers valuable insights for policymakers and stakeholders involved in groundwater management, aiding informed decision-making.

Simulation of Diurnal Evolution of Evaporation Zone during Soil Drying after Rainfall

To better understand processes involved in the evaporative drying of the soil, simulations on the dynamics of the evaporation zone, condensation zone, and dry surface layer (DSL) were conducted during a 10-day drying event under diurnal atmospheric conditions. Simulated water contents and soil temperatures matched well with the measured data in the lysimeter. Surface evaporation predominantly occurred during the early period each day, while subsurface evaporation dominated during the remaining part of the day. The evaporation zone presented a distinctly diurnal pattern, moving toward the deeper soil layer during the daytime and back toward the soil surface during the nighttime. The DSL and condensation zone, located immediately above and below the evaporation zone, respectively, also presented diurnal patterns following those of the evaporation zone. As soil drying progressed, both the position of the evaporation zone within the profile and the DSL width exhibited an overall increasing trend, reaching about 4.9 mm by the end of the study period. The occurrence of condensation zones was limited to the daytime when there was a downward surface temperature gradient present. Diurnal patterns observed in both evaporation zones and DSL could potentially be determined by quantifying changes in the near-surface profile’s soil water content, relative humidity, pressure head, and vapor density.

Effect of basalt fiber and carbon fiber on the evolution of water evaporation and cracking characteristics of silt soil

Cultivated land is prone to cracking during the high-temperature season, resulting in accelerated water evaporation, incomplete soil structure, and waste of resources caused by pollutants entering the soil. In this study, image analysis technology was used to compare the effects of two kinds of fibers on the drying and shrinkage characteristics of silt under the same volume. The results show that during cracking process, water evaporation can be divided into three phases: constant rate stage, deceleration rate stage, and residual stage. The crack rate of 0.08% basalt fiber-treated soil and 0.06% carbon fiber-treated soil is reduced by 27.66% and 27.98%, respectively. The addition of fibers acts like a bridge, narrowing the concentration of crack width from 0.2–0.8 to 0–0.6 mm, increasing short cracks of 0–5 mm and decreasing long cracks larger than 5 mm, thus reducing the soil cracking rate. With rough surface and high elastic modulus of fibers, the addition of fibers enhances the friction between soil particles to limit the movement of soil mass, and bears part of the tensile stress when cracking. It increases the tensile strength between the soil mass and effectively reduces the crack rate. It is found that the improvement effect of basalt fiber is relatively better and the economic benefit is higher under the same volume.

Study of factors affecting the remediation of contaminated soil through pneumatic fracturing and soil vapor extraction

In low-permeability soils, the effectiveness of soil vapor extraction (SVE) is often constrained, resulting in increased time and operational expenses. In this study, pneumatic fracturing and the SVE were combined to remediate low-permeability clay contaminated with ammonia gas. The soil parameters, pneumatic fracturing parameters, extraction mode, and other influencing factors were investigated via laboratory testing. The results indicated that: (1) Pneumatically induced fracturing disrupts soil structure, forming cracks and providing new pathways for ammonium gas migration; (2) the soil crack area exhibits a quadratic function relationship with both the fracturing pressure and frequency, and the soil crack area increases with higher pneumatic frequencies, leading to a faster pneumatic pressure decline; (3) a denser network of pathways emerges within the soil due to the reduced distance between the two pneumatic fracturing points, consequently enhancing soil permeability and increasing pollutant elimination efficiency; (4) the ammonium gas removal efficiency gradually increases with an increase in the extracted vapor flow rate, but there is an optimal extraction flow rate (9 L/min); (5) continuous extraction combined with gas injection effectively ameliorates the issue of prolonged fluctuations in ammonium gas concentration during the later stages of extraction. (6) Fracturing and extraction reduce the moisture content of the surrounding soil. The results demonstrated the feasibility and superiority of pneumatic pre-fracturing extraction in low-permeability soils.

Prediction of the weighted-mean soil water diffusivity in supporting the falling rate stage of evaporation

Daily soil evaporation from drying soil can be described as isothermal linear diffusion process, resulting in a simple equation for estimating soil evaporation rate. However, determining soil water diffusivity and subsequently the crucial parameter of weighted-mean diffusivity, essential for estimating soil evaporation rate, is challenging and time-consuming. In this paper, the soil water diffusivity was re-evaluated by considering the effect of film flow, a phenomenon often overlooked but recently argued by Wang et al. (2019, https://doi.org/10.1029/2019WR025003) as the dominant process in the falling rate stage of evaporation. Theoretical derivation reveals a universal relationship between soil water diffusivity and matric potential, independent of soil types. Additionally, soil water diffusivity can be expressed in the form of an exponential function, a form commonly assumed empirically in the literature. Testing with various datasets suggests that the theoretically derived soil water diffusivity generally agrees closely with observations for matric potentials less than about −1 m, wherein the diffusivity accounting for capillary flow shows significant underestimation. Furthermore, a simple function is derived for estimating the weighted-mean diffusivity, enabling a direct estimation of soil evaporation rates in the falling rate stage. Testing with various data sets of different soil types and ambient conditions generally demonstrates close agreements between the estimated soil evaporation rates and observations, indicating that the developed method provides a robust estimation of the weighted-mean soil water diffusivity. When the initial matric potential of the linear diffusion process of drying is higher than about −1 m, which usually occurs under very high atmospheric demand conditions or for very coarse-textured soils, however, the effects of capillary flow were found to be important and need consideration. The effects of vapor diffusion were also discussed and found to have a negligible impact on the estimation of weighted-mean soil water diffusivity.

Ecosystem CO2 Exchange and Its Environmental Regulation of a Restored Wetland in the Liaohe River Estuary

Coastal wetlands are important carbon sinks， and they contribute to reducing the effects of global warming. This study used the eddy covariance method to detect the CO2 flux in the restoration wetland of the Liaohe River estuary in 2021 and investigate the characteristics of ecosystem CO2 exchange and its environmental control factors. The aim was to assess the carbon source/sink capacity of salt marshes in the restored area and to provide data support and theoretical basis for evaluating the effectiveness of ecological restoration projects. The study revealed "U" curves in spring and autumn， "V" curves in summer， and horizontal lines in winter for the average daily variation curve of net ecosystem CO2 exchange （NEE） in the restored area. Its carbon sink efficiencies were -40.06， -63.62， 2.33， and 34.43 g·m-2 in the spring， summer， autumn， and winter， respectively. In the restored area， the daily cumulative variation in NEE was "V" shaped， and the monthly cumulative changes in NEE， ecosystem respiration （Reco）， and gross primary productivity （GPP） were obviously different. Photosynthetically active radiation （PAR） was an important regulation factor of daytime NEE in the restored area in 2021， and they displayed a rectangular hyperbolic relationship. PAR could explain 53% of the variation in the daytime NEE. Air temperature （Ta） was the main control factor of Reco，night， and there was an exponential relationship between them. When Ta < 5.5 ℃， the temperature sensitivity of ecosystem respiration （Q10） was 2.19， and Ta could explain 42% of the variation in the Reco，night； when Ta ≥ 5.5 ℃， the Q10 was 1.81， and Ta could explain 51% of the variation in the Reco，night. Additionally， there were significant linear negative correlations between NEE and both soil water content （SWC） and vapor pressure deficit （VPD）， whereas NEE was not significantly correlated with soil temperature （Ts） or relative humidity （RH）. In 2021， the restored wetland in the Liaohe River estuary acted as a CO2 sink， and the total net carbon sequestration was -66.89 g·m-2. The restored salt plays a role as an important carbon sink and has long-term carbon sequestration potential.

Long-term monthly 0.05° terrestrial evapotranspiration dataset (1982–2018) for the Tibetan Plateau

Abstract. Evapotranspiration (ET) plays a crucial role in the water balance of the Tibetan Plateau (TP), often referred to as the “Asian water tower” region. However, accurately monitoring and comprehending the spatial and temporal variations of ET components (including soil evaporation Es, canopy transpiration Ec, and intercepted water evaporation Ew) in this remote area remains a significant challenge due to the limited availability of observational data. This study generates a 37-year dataset (1982–2018) of monthly ET components for the TP using the MOD16-STM (MOD16 soil texture model). This model utilizes up-to-date soil properties, meteorological data, and remote sensing datasets. The estimated ET results strongly correlate with measurements from nine flux towers, demonstrating a low root mean square error of 13.48 mm per month, a mean bias of 2.85 mm per month, a coefficient of determination of 0.83, and an index of agreement of 0.92. The annual average ET for the entire TP, defined as elevations higher than 2500 m, is approximately 0.93(± 0.037) × 103 Gt yr−1. The predominant contributor to ET on the TP is Es, accounting for 84 % of the total ET. Our findings reveal a noteworthy upward trend in ET in most central and eastern parts of the TP, with a rate of approximately 1–4 mm yr−1 (p<0.05) and a significant downward trend with rates between −3 and 1 mm yr−1 in the northwestern part of TP during the period from 1982 to 2018. The average annual increase in ET for the entire TP over the past 37 years is approximately 0.96 mm yr−1. This upward trend can be attributed to the TP's warming and wetting climate conditions. The MOD16-STM ET dataset demonstrates a reliable performance across the TP compared to previous research outcomes. This dataset is valuable for research on water resource management, drought monitoring, and ecological studies. The entire dataset is freely accessible through the Science Data Bank (https://doi.org/10.11922/sciencedb.00020, Ma et al., 2021) and the National Tibetan Plateau Data Center (TPDC) (https://doi.org/10.11888/Terre.tpdc.271913, Yuan, 2021).

Exploring the Influence of Climate Change on Earthen Embankments with Expansive Soil

Climate change is known to cause alterations in weather patterns and disturb the natural equilibrium. Changes in climatic conditions lead to increased environmental stress on embankments, which can result in slope failures. Due to wetting–drying cycles, expansive clayey soil often swells and shrinks, and matric suction is a major factor that controls the behavior. Increased temperature accelerates soil evaporation and drying, which can cause desiccation cracks, while precipitation can rapidly reduce soil shear strength. Desiccated slopes on embankments built with such soils can cause surficial slope failures after intense precipitation. This study used slope stability analysis to quantify how climate-change-induced extreme weather affects embankments. Historic extreme climatic events were used as a baseline to estimate future extremes. CMIP6 provided historical and future climatic data for the study area. An embankment was numerically modeled to evaluate the effect on slope stability due to the precipitation change induced by climate change. Coupled hydro-mechanical finite element analyses used a two-dimensional transient unsaturated seepage model and a limit equilibrium slope stability model. The study found that extreme climatic interactions like precipitation and temperature due to climate change may reduce embankment slope safety. The reduction in the stability of the embankment due to increased precipitation resulting from different greenhouse gas emission scenarios was investigated. The use of unsaturated soil strength and variation of permeability with suction, along with the phase transition of these earthen embankments from near-dry to near-saturated, shows how unsaturated soil mechanics and the hydro-mechanical model can identify climate change issues on critical geotechnical infrastructure.

Analytical model for bare soil evaporation dynamics following wetting with concurrent internal drainage

Under natural conditions, infiltrated rainwater redistributed into the soil profile, becomes partially sheltered from surface evaporative losses relative to undrained wet surfaces. Surface evaporation rates and internal drainage dynamics are both sensitive to soil hydraulic properties and initial soil hydration state. We report a novel analytical framework for quantifying surface evaporation rates with concurrent internal drainage, considering soil properties and dynamic surface evaporation resistance. Interplay among soil hydraulic properties, boundary conditions, and atmospheric demand result in nonlinear relationships between cumulative evaporative losses and initial water content. The new analytical solution shows good agreement with laboratory column experiments and literature data. Results highlight the role of soil texture on evaporative losses and the nonlinear effects of initial wetness on evaporation. The largest evaporative losses per rainfall amount are predicted for small rainfall events over initially dry loamy soils due to the detention of infiltrated rainwater near the surface for soils with large porosity and low hydraulic conductivity. The analytical framework uses readily available parameters hence can be implemented in land surface models to explicitly consider how soil properties and rainfall event size affect surface evaporation dynamics.

The transmission of isotopic signals from precipitation to groundwater and its controls: An experimental study with soil cylinders of various soil textures and burial depths in a monsoon region

The use of stable isotopic composition in groundwater as a paleoclimatic proxy assumes that the isotopic values in groundwater are inherited from the corresponding values in the source precipitation. However, several studies have observed that groundwater δ18O (δ18Og) is not always in accordance with the average δ18O of precipitation (δ18Op). The cause of this inconsistency is still the subject of debate. Significant reduced isotopic variability and potential deviations from precipitation to groundwater because of the aquifer itself (e.g., groundwater buried depths and soil texture) and external precipitation characteristics (e.g., rainfall intensity and duration) have been poorly quantified in terms of identifying the dominant factors. To investigate the controls on the transmission of isotopic signals from precipitation to groundwater, we present new stable isotope data for precipitation and groundwater from an experimental site using eight soil cylinders of different soil textures and burial depths in a monsoon region. We collected data at inter-event sampling intervals (30 min) during and after two heavy precipitation events (daily amounts higher than 10 mm). Our results demonstrated a significant disparity between the average isotopic values of heavy rainfall and light rainfall, despite both exhibiting decreasing isotopic patterns throughout the course of the rainfall event. Various degrees of attenuation of isotopic variations were found in outflow waters with different groundwater burial depths (GBDs) and soil textures after rainfall events. The isotopic variations were not synchronized with the outflow changes. Specifically, there were evident outflow lags in response to heavy rainfall, especially in the lysimeters with GBDs deeper than 0.5 m, while the greatest isotopic variation was observed in the early infiltrating stage. Redundancy analysis indicated that precipitation amount was the most important contributor to the outflow variation (∼51 %, p < 0.05), while GBD was the key factor for isotopic temporal variation (∼52 %, p < 0.05). These results concurred with the clustering of principal component analysis results. The mixing of soil water and heavy rainfall event components was observed in four lysimeters with mixing proportions fP varying in the range of 7 %–51 %, indicating the effective recharge from heavy rainfall. Soil evaporation was highlighted with samples located parallel to the local meteoric water line. It is recommended that groundwater isotopes in paleoclimatic studies are used with additional constraints that consider disproportionate recharge from intense rainfall, past chaotic fluctuations in groundwater dynamics, and distortions introduced by evaporation.

Evapotranspiration and potential water saving effect evaluation of mulched maize fields in China

To alleviate the contradiction between crop evapotranspiration (ET) and available water resources, and to develop agricultural production, mulched irrigation, as a water saving technology, is popularized in arid areas of China. However, the observations of ET in long-term mulched farmlands are scarce, so the inter-annual variation and controlling factors of ET after mulching remain uncertain, and the overall water saving effect of mulching in arid areas has not been quantified. Therefore, we conducted the observation experiments (2007–2021) on a mulched maize field, applied the modified Shuttleworth-Wallace model and obtained multi-source data statistics to fill in the gaps in the previous research. The results showed that the mean ET in the past 15 years was 521.68 mm, and the arid areas faced more severe water demand pressure. The inter-annual ET trend of the mulched maize field increased significantly, mainly caused by the reference evapotranspiration (ET0), while the inter-annual fluctuation was mainly attributed to the crop coefficient (Kc). The contribution of plant transpiration (Tr) to ET was always greater than that of soil evaporation (Es), and the contribution of solar radiation (Rs) to ET was the largest among environmental factors. In addition, based on observation data and model simulation, it was revealed that the water saving amount and ratio of the long-term mulched maize field were estimated to be 83.8 mm and 13.3 %, respectively. Furthermore, the statistical results from 49 sites in five provinces (regions) in Northwest China showed that compared with the agricultural water use in the recent 10 years, the mean annual total potential water saving amount and ratio of the mulched maize field were 2.2 billion m3 and 2.5 %, respectively. Our study will provide important guidance for understanding the variation of crop ET and water resources allocation.

Quantifying the Spatiotemporal Changes in Evapotranspiration and Its Components Driven by Vegetation Greening and Climate Change in the Northern Foot of Yinshan Mountain

Evapotranspiration (E), a pivotal phenomenon inherent to hydrological and thermal dynamics, assumes a position of utmost importance within the intricate framework of the water–energy nexus. However, the quantitative study of E on a large scale for the “Grain for Green” projects under the backdrop of climate change is still lacking. Consequently, this study examined the interannual variations and spatial distribution patterns of E, transpiration (Et), and soil evaporation (Eb) in the Northern Foot of Yinshan Mountain (NFYM) between 2000 and 2020 and quantified the contributions of climate change and vegetation greening to the changes in E, Et, and Eb. Results showed that E (2.47 mm/a, p &lt; 0.01), Et (1.30 mm/a, p &lt; 0.01), and Eb (1.06 mm/a, p &lt; 0.01) all exhibited a significant increasing trend during 2000–2020. Notably, vegetation greening emerged as the predominant impetus underpinning the augmentation of both E and Eb, augmenting their rates by 0.49 mm/a and 0.57 mm/a, respectively. In terms of Et, meteorological factors emerged as the primary catalysts, with temperature (Temp) assuming a predominant role by augmenting Et at a rate of 0.35 mm/a. Temp, Precipitation (Pre), and leaf area index (LAI) collectively dominated the proportional distribution of E, accounting for shares of 32.75%, 28.43%, and 25.01%, respectively. Within the spectrum of predominant drivers influencing Et, Temp exerted the most substantial influence, commanding the largest proportion at 33.83%. For Eb, the preeminent determinants were recognized as LAI and Temp, collectively constituting a substantial portion of the study area, accounting for 32.10% and 29.50%, respectively. The LAI exerted a pronounced direct influence on the Et, with no significant effects on E and bare Eb. Wind speed (WS) had a substantial direct impact on both E and Et. Pre exhibited a strong direct influence on E, Et, and Eb. Relative humidity (RH) significantly affected E directly. Temp primarily influenced Eb indirectly through radiation (Rad). Rad exerted a significant direct inhibitory effect on Eb. These findings significantly advanced our mechanistic understanding of how E and its components in the NFYM respond to climate change and vegetation greening, thus providing a robust basis for formulating strategies related to regional ecological conservation and water resources management, as well as supplying theoretical underpinnings for constructing sustainable vegetation restoration strategies involving water resources in the region.

Quinoa growth and yield, soil water dynamics, root growth, and water use indicators in response to deficit irrigation and planting methods

To address the growing issue of scarce water in the arid and semi-arid areas, it is essential to investigate the potential of drought tolerant crops and implement promising farm management strategies to improve water productivity and yield production. Therefore, a split plot experiment to investigate how different irrigation levels (I-1:100% water requirement (WR), I-2:75%WR, and I-3: 50%WR) and planting methods (P-1: basin, P-2: on-ridge, and, P-3: in-furrow) interact and affect quinoa water use, yield, root growth, and water productivity in southern Iran over two growing seasons. The results showed high seasonal crop evapotranspiration (993–1030 mm) in I-1 as a result of the high advection ratio (α), which ranged from 1.02 to 1.46 from the early vegetative to the seed filling stages. The P-3 increased transpiration rate by 4.5% and 7.7%, and decreased soil evaporation by 17% and 29% compared to P-1 and P-2, respectively. Single (Kc) and dual (Kcb + Ke) crop coefficients varied between 0.41 and 1.38 over the two growing seasons. Grain yield in P-3 were 25%, 34%, and 44% higher compared to P-1 and P-2 under I-1, I-2 and I-3, respectively. The study revealed that nearly 67% and 80% of the total root dry matter was in the 0–30 cm and 0–60 cm of the soil profile in all experimental treatments, respectively. Regardless of irrigation treatment, root length density (RLD) and root mass density (RMD) were found to be 18.9% and 15.7% lower in P-1’s top 0–20 cm of the soil profile than those obtained in P-2 and P-3, respectively. Analyses showed that the increased root length in deeper soil layers contributed to higher soil water uptake, and consequently higher crop water productivity. In addition, root-to-shoot ratio increased as the amount of the applied irrigation water was decreased. Quinoa exhibited the highest acclimation to water stress in P-3 based on water stress sensitivity coefficients (λi) and yield response factor (Ky) values. Crop water productivity (WPC) and irrigation water productivity (WPI) for grain yield varied between 0.17 and 0.28 kg m−3. In conclusion, in terms of grain yield, shoot and root dry matter and water productivity, I-2 and P-3 (75% WR irrigation level and in-furrow planting method treatment) is recommended as the optimum water and planting management strategy for quinoa cultivation in the study area as a measure to address water scarcity and food sustainability. Still, to improve yield and irrigation water efficiency, the effect of soil management practices such as mulching and organic amendments on soil water retention and nutrient availability for quinoa should be investigated.