Water Supply Balance Research Articles

Quantitative performance analysis of anion-exchange membrane fuel cells with in-plane and through-plane water transport

Effective water management is crucial in anion-exchange membrane fuel cells (AEMFCs) due to water's dual role as a reactant during alkaline oxygen reduction and a product of alkaline hydroxide oxidation. Meanwhile, both hydroxide conduction and water transport in polymer electrolytes are highly dependent on the hydration level. Therefore, a three-dimensional multi-physics model is developed to investigate the critical role of ionic and water transport parameters of the electrolyte on AEMFC performance. Additionally, detailed water distribution analysis is used to reveal its fundamental mechanism. The results reveal that extremely inhomogeneous water distribution and cathode water starvation are the main causes of the poor cell performance. Moreover, increasing membrane water diffusivity, water conversion, and decreasing the electro-osmotic drag coefficient all contribute to better cell performance through improved water balance and cathode water supply. Among these, cell performance is most sensitive to membrane water diffusivity, with a 40 % increase in peak power density when it is increased from 10−10 m2 s−1 to 10−9 m2 s−1. Although high ionic conductivity improves cell performance by directly reducing ohmic impedance, it also results in a more inhomogeneous distribution of water in the whole cell, so that a four-fold increase in ionic conductivity only yields a 62 % increase in peak power density.

A system dynamics approach to management of water resources in Qatar

Rapid global population growth and extensive urbanization threaten water sustainability, hindering sustainable development. This issue is particularly acute in arid regions such as the Gulf Cooperation Council (GCC), where the scarce natural water resources are overexploited. Effective water resource management (WRM) is pivotal in overcoming this challenge. This holistic study presents an innovative approach to address water sustainability at a national scale by developing a WRM decision support system (DSS) leveraging system dynamics modeling (SDM). Employing a unique scenario design framework developed in this study, the DSS simulates Qatar's water resource system behavior for 2021 to 2070 according to nine clustered policy scenarios presenting different degrees of sustainability designed accounting for changes in physical, environmental, and socioeconomic patterns. Our results reveal that the “business-as-usual” (BAU) WRM policy can balance water supply and demand for only 32 years. According to the best policy scenario, the sustainability of the water supply could be ensured for up to 50 years by increasing the water supply by 10 % and reducing consumption by 10 %. Additionally, to aid policymakers in fostering water resource sustainability, groundwater conservation strategies are proposed using the unique scenario design framework by limiting the yield to the safe abstraction level and emphasizing the significance of preserving non-renewable groundwater resources as a “backstop” resource for the country. While marking the first holistic research study in Qatar by utilizing the SDM approach to tackle national-scale WRM challenges, the established WRM DSS model is equally applicable to other GCC countries and similar arid regions.

Water Supply Planning in the Face of Drought and Ecosystem Flows: Examining the Impact of the Bay-Delta Plan on Bay Area Water Supply.

In California, recent Bay-Delta Plan legislation attempts to balance water supply and ecosystem protection by requiring 40% of the flow to remain in-stream in the Tuolumne River from February through June. Serious questions remain about what this means for the Bay Area water supply, especially during drought. Our work develops a new approach to analyze how in-stream flow policy coupled with climate change could impact regional water supply over the coming decades. Results show that the new in-stream flow demand would exceed urban water deliveries in a typical year. In wet years, water supply performance is minimally impacted, but in drought, the policy can lead to less water in storage, delayed reservoir recovery, and increased time at critically low storage. Storage impact exceeding 50 000 acre-feet (60 million m3) is anticipated with at least 18% frequency, demonstrating that, climate uncertainty notwithstanding, this impact must be planned for and managed to ensure a reliable future water supply.

WITHDRAWN: A novel step function approach for reservoir operation to balance water storage and flood control during extreme rainfall events

Reservoir operation is crucial during extreme rainfall events which impact flooding and water supply. Simple models with upgraded operating rules can accurately simulate reservoir operations and used as a tool to investigate operations during extreme rainfall events. In this study, a step function for reservoir operation, that can be upgraded based on historical flood events, was developed and embedded with a simple box model. This model simplifies the simulation of controlled reservoir operation and can be integrated with hydrologic and hydraulic models for the assessment of the impacts of controlled reservoir operation. Chembarambakkam, a large water supply reservoir in Chennai city, India, was used to assess the performance of the developed model. The parameters of the box model were calibrated and validated with an error estimation of 11 and 13 % for inflow, 21 and 22% for outflow, and 15 and 16% for water level, respectively. Furthermore, a massive flood event that occurred in Chennai in 2015 was evaluated with various combinations of reservoir operations using the developed approach. The sensitivity analysis of the parameters shows that the initial water level in the Chembarambakkam reservoir plays a substantial role in balancing water supply and flood mitigation. Restraining initial water levels from 50 to 75 % of storage helps to reduce the flood peaks from 14 to 38 % and inundation extents by 3.19 to 5.18 km2 besides the reliable storage of 81.50 % for water supply. Thus, the proposed box model was proven to be useful in controlled reservoir operation during extreme rainfall events.

Withdrawn: A novel step function approach for reservoir operation to balance water storage and flood control during extreme rainfall events

Reservoir operation is crucial during extreme rainfall events which impact flooding and water supply. Simple models with upgraded operating rules can accurately simulate reservoir operations and used as a tool to investigate operations during extreme rainfall events. In this study, a step function for reservoir operation, that can be upgraded based on historical flood events, was developed and embedded with a simple box model. This model simplifies the simulation of controlled reservoir operation and can be integrated with hydrologic and hydraulic models for the assessment of the impacts of controlled reservoir operation. Chembarambakkam, a large water supply reservoir in Chennai city, India, was used to assess the performance of the developed model. The parameters of the box model were calibrated and validated with an error estimation of 11 and 13 % for inflow, 21 and 22% for outflow, and 15 and 16% for water level, respectively. Furthermore, a massive flood event that occurred in Chennai in 2015 was evaluated with various combinations of reservoir operations using the developed approach. The sensitivity analysis of the parameters shows that the initial water level in the Chembarambakkam reservoir plays a substantial role in balancing water supply and flood mitigation. Restraining initial water levels from 50 to 75 % of storage helps to reduce the flood peaks from 14 to 38 % and inundation extents by 3.19 to 5.18 km2 besides the reliable storage of 81.50 % for water supply. Thus, the proposed box model was proven to be useful in controlled reservoir operation during extreme rainfall events.

Numerical Modelling of a Dam-Regulated River Network for Balancing Water Supply and Ecological Flow Downstream

Dam operation is regarded as an effective way to increase water, food, and energy security for society. However, with the increasing water demand and frequent extreme droughts, numerous rivers worldwide go through periods of water scarcity and water ecosystem deterioration to varying degrees. Balancing the water supply and ecological flow of the dam-regulated river network is essential in the context of river restoration. In this study, we proposed a hydrodynamic and water quality model of a dam-regulated river network balancing water supply and ecological flow using the Environmental Fluid Dynamics Code (EFDC). A section of Jinjiang watershed located in the southwestern of China was chosen as the study area. Firstly, the model was calibrated and validated. By comparing the simulated values with the measured values, the statistical analysis results showed that the relative root mean-squared error (RRMSE) values of water level, COD and NH3-N were 5.5–8.1%, 23.6% and 28.4%, respectively, indicating an adequate degree of agreement between simulation and observation. Based on the established model, dam operation schemes under a dry hydrologic scenario and emergency contamination scenario were formulated to ensure the requirement of ecological water flow and water quality simultaneously. For the dry hydrologic scenario, the ecological water requirement could be satisfied through the dam operation. However, in an emergency contamination scenario, regional water quality requirements cannot be met through dam operation. The dam operation only plays a role in controlling the scope of pollution. This study is expected to provide scientific support for dam-regulated river network management and downstream river ecosystem protection.

Spatial-Temporal Changes in Water Supply and Demand in the Citarum Watershed, West Java, Indonesia Using a Geospatial Approach

Balancing water supply demand is vital for sustaining livelihoods. Spatial mapping and calculating water yield dynamics due to land use changes over decades are needed to manage land resources and formulate ecological protection policies. This study mapped the supply, demand, and matching status of water product service using the Integrated Valuation of Ecosystem Service and Tradeoff (InVEST) biophysical models in the Citarum Watershed (CW) in 2000, 2010, and 2020. Moreover, this study used Exploratory Spatial Data Analysis (ESDA) and Geographic Information System (GIS) techniques to study the agglomeration characteristics and evolutionary trajectories of supply–demand over two decades. The results showed that between 2000–2010 and 2010–2020, the water supply decreased by 19.01 × 108 m3 (18.28%) and 12.97 × 108 m3 (15.27%), respectively. However, the water demand in the same period increased by 6.17 × 108 m3 (23%) and 15.74 × 108 m3 (47%), respectively. Over the decades, the contribution of land use land cover (LULC) changes to variations in water supply has yielded values ranging from 2.87% to 6.37%. The analysis of the water supply–demand imbalance indicated that the entire CW experienced water shortage, and the type of spatial matching for supply and demand is dominated by a high supply and high demand class (16.09% of the total area). Based on the level of water deficit calculation, the upstream and downstream areas were identified as zones that require ecological conservation, while the middle CW area requires ecological restoration or ecological improvement.

Seasonal variations in water uptake and transpiration for plants in a karst critical zone in China

Despite substantial drought conditions in the karst critical zone (KCZ), the KCZ landscapes are often covered with forest woody plants. However, it is not well understood how these plants balance water supply and demand to survive in such a water-limited environment. This study investigated the water uptake and transpiration relationships of four coexisting woody species in a subtropical karst forest ecosystem using measurements of microclimate, soil moisture, stable isotopes (δ18O, δ2H, and δ13C), intrinsic water-use efficiency (WUEi), sap flow, and rooting depth. The focus was on identifying differences within- and between-species across soil- and rock-dominated habitats (SDH and RDH) during the rainy growing season (September 2017) and dry season (February 2018). Species across both habitats tended to have higher transpiration with lower WUEi during the rainy season and lower transpiration with higher WUEi during the dry season. Compared to those in the SDH, species in the RDH showed lower transpiration with higher WUEi in both seasons. The dominant water sources were soil water and rainwater for supporting rainy-season transpiration in the SDH and RDH, respectively, and groundwater was the main water source for supporting dry-season transpiration in both habitats. A clear ecohydrological niche differentiation was also revealed among species. Across both habitats, shallower-rooted species with higher soil-water uptake, compared to deeper-rooted species with higher groundwater uptake, showed higher transpiration and lower WUEi during the rainy season and vice versa during the dry season. This study provides integrated insights into how forest woody plants in the KCZ regulate transpiration and WUEi in response to drought stress through interactions with seasonal water sources in the environment.

Evaluating the Effects of Climate Change and Human Activities on the Seasonal Trends and Spatial Heterogeneity of Soil Moisture

Soil moisture (SM), as a crucial variable in the soil–vegetation–atmosphere continuum, plays an important role in the terrestrial water cycle. Analyzing SM’s variation and driver factors is crucial to maintaining ecosystem diversity on the Tibetan Plateau (TP) and ensuring food security as well as water supply balance in developing countries. Gradual wetting of the soil has been detected and attributed to precipitation in this area. However, there is still a gap in understanding the potential mechanisms. It is unclear whether the greening, glacier melting, and different vegetation degradation caused by asymmetrical climate change and intensified human activities have significantly affected the balance of SM. Here, to test the hypothesis that heterogeneous SM caused by precipitation was subject to temperatures and anthropogenic constraints, GLDAS-2.1 (Global Land Data Assimilation System-2.1) SM products combined with the statistical downscaling and Geographic detectors were applied. The results revealed that: (1) Seasonal SM gradually increased (p < 0.05), while SM deficit frequently appeared with exposure to extreme climates, such as in the summer of 2010 and 2013, and changed into a pattern of precipitation transport to western dry lands in autumn. (2) There was a synergistic reaction between greening and local moisture in autumn. SM was dominated by low temperature (TMN) in winter, warming indirectly regulated SM by exacerbating the thawing of glaciers and permafrost. The spatial coupling between the faster rising rate of TMN and the frozen soil might further aggravate the imbalance of SM. (3) The land cover’s mutual transformation principally affected SM in spring and autumn, and degradation accelerated the loss of SM replenished by precipitation. (4) Land cover responses were different; SM in grassland was less affected by external disturbance, while degraded woodland and shrub performed adaptive feedback under dry environments, SM increased by 0.05 and 0.04 m3/(m3 10a), respectively. Our research provides a scientific basis for improving hydrological models and developing vegetation restoration strategies for long-term adaptation to TP-changing environments.

Mixed temperature gradient evaporator for solar steam generation

Solar-driven interfacial water evaporation enables us to build flexible, extensible, and decentralized evaporators with zero carbon dioxide emission. The theoretical limit of evaporation rate is not tolerable for users with large-capacity water requirements. Here, we report how a wicking solar absorber with a columnar structure can generate a counterintuitive evaporation enhancement mechanism: both positive- and negative-temperature gradients, which we term mixed temperature gradient, are generated in the wicking material. This allows a ∼3.8 times equivalent evaporation rate compared with the theoretical limit. We demonstrate that the mixed temperature gradient is a new thermal equilibrium achieved by the combined effect of solar heating and evaporative cooling. Importantly, the sidewall height should be consistent with the capillary height dominated by imbibition and diffusion. Specifically, designing a solar absorber with a balanced water supply and demand allows a higher evaporation rate in both light and darkness. • A mixed temperature gradient of the interfacial solar steam generator is reported • Efficient management of water and heat transportation are synchronously achieved • The underlying evaporation enhancement mechanism is discussed • An evaporation rate of up to 5.62 kg m −2 h −1 under one sun is obtained Li et al. describe the mixed temperature gradient of solar steam generators enabled by solar heating and evaporative cooling. This evaporator demonstrates 5.62 and 2.77 kg m −2 h −1 evaporation rates in light and darkness, respectively, opening up the development of flexible, extensible, and sustainable solar stills to produce clean water.

Study on the Spatial Allocation of Receding Land and Water Reduction under Water Resource Constraints in Arid Zones

The withdrawal of cultivated land policy is not only an important task to promote cultivated land rest and alleviate the contradiction between supply and demand of water resources in arid areas, but also an important way to realize the sustainable development of agriculture and social economy. This study adopted the minimum per capita area method, ESPR (Exposure-Sensitivity-Pressure-Response) vulnerability assessment model, grey prediction model, and GIS spatial analysis. Furthermore, based on the characteristics of water resource constraints in the arid zone, Manas County was used as the study area. By exploring and analyzing the area of land retreat, through identifying its occurrence and position, the spatial zoning layout of land retreat can be realized to guarantee the effective implementation of water retreat and reduction. The following points were noted from the results: (1) the upper and lower limits of the area of receding land in Manas County were measured using the minimum per capita area method and the principle of balancing water supply and demand. The receding land in Manas County measured 16,493.68–20,749.90 hm2, which accounted for 24.31–30.58% of the total area of cultivated land. (2) The results obtained from constructing the ESPR vulnerability assessment model, used to assess the vulnerability of cultivated land in Manas County, showed that the overall vulnerability of cultivated land in Manas County was high, with 94.74% of the county’s cultivated land being moderately vulnerable or worse, which necessitates the optimization of land use. (3) The area of cultivated land withdrawal under the water resource constraint was used as a constraint for the withdrawal of cultivated land. Based on the evaluation of the vulnerability of cultivated land, with the results arranged from small to large, it was concluded that the area of cultivated land withdrawal in Manas County could reach up to 16,787.34 hm2. There are four types of cultivated land withdrawals: desertified withdrawal, saline withdrawal, groundwater overexploitation withdrawal, and soil contamination withdrawal. The results of this study can provide a reference for Manas County to scientifically formulate a reasonable and orderly withdrawal system of farmland to reduce water use.

Planning for effective water management: an evaluation of water management plans in California

Facing pressures to contend with continual changes in physical availability, to balance water supply with environmental and social impacts, and to build resilience to environmental hazards such as droughts and climate change, water managers increasingly use management plans as a blueprint for managing water. We apply qualitative content analysis to evaluate water management plans from diverse water and land use organizations in California’s Central Valley. To understand whether plans are working toward holistic, multi-dimensional management, we assess plans’ coverage of water supply, environmental, and socioeconomic dimensions of water use, as well as the quality and implementability of the plans. The plans provide a strong assessment of water supplies and indicate progression toward integrated water resource management. However, we identify gaps in managing water for the environment, considering socioeconomic and distributional impacts, planning for future drought and climate change, and effective coordination with other water agencies and the public.

Optimization of biochar systems in the water-food-energy-carbon nexus for sustainable circular agriculture

The increasing pressures of global warming, population growth and epidemic occurrence are causing challenges in meeting the growing requirements for water, energy and food. In particular, the contradiction between the supply and demand for water, food, and energy is exacerbated by inefficient resource utilization and carbon emission increase. Incorporation of the interlinked aspects of water, energy, food and carbon emissions from agricultural systems into one water-food-energy-carbon nexus facilitates integrated resource management. Biochar application to farmland is a potential strategy for carbon management and agricultural productivity improvement. The integration of biochar systems and the water-food-energy-carbon nexus is an efficient and coordinated alternative method for sustainable agricultural management and a crucial strategy for addressing water, energy and food security issues. Accordingly, this paper proposes an approach for the synergistic regulation of water, land, energy, and carbon emissions in a circular agricultural system by balancing water supply and demand, land allocation, electricity consumption, and economic upgrading principles. A two-stage circular agriculture framework is constructed, with biochar and electricity generated from agricultural residues at the first stage and employed at the second stage. Economic-environmental-energy harmonization is considered in the methodology, and the agrotechnical potential of biochar is quantified via crop yield increase and greenhouse gas emission reduction functions. This approach can assist decision makers in providing the best policy options given certain agricultural resources to achieve the maximum economic performance of the system while minimizing environmental side effects. In this paper, the model framework is applied to the Sanjiang Plain in northeastern China to verify the feasibility of the approach. The results indicate that the external electricity demand is reduced by 87.8% due to the generation of biofuels. Cropland greenhouse gas emissions are reduced by 34.09%–67.06% via the application of biochar. This study proposes an optimization method with important implications for the improvement of regional cropland management techniques and development of sustainable circular agriculture. This methodology can be extended to other agriculture-centered regions with limited resources and environmental problems.

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In the perennial plantations it is possible to apply spray irrigation method instead of drip irrigation, in case of which the drippers are replaced with the holes made on the pipes, wherefrom the water is supplied through the spraying jet. Upon the hydraulic calculations water flow pressure in water supply pipes, supplied water yields and diameter of the opened holes have been estimated by means of which the balanced water supply is ensured. Introduction of the recommended spray method will enable to significantly reduce the operational costs of irrigation systems.

A bioinspired 3D solar evaporator with balanced water supply and evaporation for highly efficient photothermal steam generation

Inspired by a lotus leaf, a 3D carbon fibre-cotton-based conical water evaporator with tuneable water supply is designed. By changing the number of branch water paths, a balance between the water supply flux and evaporation rate is achieved.

Changing climate drives future streamflow declines and challenges in meeting water demand across the southwestern United States

Society and the environment in the arid southwestern United States depend on reliable water availability, yet current water use outpaces supply. Water demand is projected to grow in the future and climate change is expected to reduce supply. To adapt, water managers need robust estimates of future regional water supply to support management decisions. To address this need, we estimate future streamflow in seven water resource regions in the southwestern U.S. using a new SPAtially Referenced Regressions On Watershed attributes (SPARROW) streamflow model. We present streamflow projections corresponding to input data from seven climate models and two greenhouse gas Representative Concentration Pathways (RCP4.5 and 8.5) for three, thirty-year intervals centered on the 2030s, 2050s, and 2080s, and for a historical thirty year interval centered on the 1990s. Across water resource regions, about half of the RCP4.5 models (51%) and two thirds of the RCP8.5 models (67%) indicate decreases in streamflow in the 2080s relative to the historical period. Models project maximum decreases in streamflow of 36–80% in all water resource regions for all periods and RCPs relative to historical streamflow, and maximum streamflow decreases of up to 20–45% in the 2080s at sites along the Colorado River used for measuring compliance with interstate and international water agreements. Headwaters are projected to experience the greatest declines, with substantial downstream implications. Among these estimates, the streamflows from models forced with RCP8.5 tend to be lower than those forced with RCP4.5. Not all climate models, times, and RCPs project widespread streamflow declines. The most ubiquitous streamflow increases are projected to occur in the 2030s under RCP4.5. Later time periods and enhanced greenhouse gas forcings indicate smaller regions of streamflow increase and lower accumulated streamflows, suggesting that limiting or reducing greenhouse gas concentrations could support future water availability. Although some possible streamflow increases are promising, the modest and spatially limited increases in streamflow projected for later time periods are still unlikely to be sufficient to meet the projected water demand. These results inform the likelihood of future water agreement compliance, and support developing strategies to balance water supply and demand.

Influence of Water Stress Levels on the Yield and Lycopene Content of Tomato

Good water supply practice provides benefits such as water and energy conservation but also alters the quality of yield. These effects of irrigation on yield quantity and quality are widely researched in the case of many plants. In tomato it can affect the soluble solids content positively together with a slight reduction in yield quantity as confirmed by many studies. There are results in the literature regarding its effect on carotenoid composition and lycopene content as well, but the effect on lycopene isomers has not been revealed yet. In this study, we investigated how different water supply levels affect yield quantity and quality, focusing on lycopene components. A two-year open field irrigation experiment with a center pivot capable of variable rate irrigation was conducted on processing tomato. The water supply levels were 100%, 75%, and 50% of ETc (crop evapotranspiration) until the beginning of the ripening stage, calculated by AquaCrop compared to control without regular irrigation. The results suggested that 75% of ETc supplied till the beginning of ripening, was a balanced water supply level regarding yield quantity, soluble solids content and lycopene concentration and yields, such as higher concentration and ratio to total carotenoids. The evaluation of cis-lycopene concentration and ratio to all-trans did not show clear results in the two years.

Threshold Vegetation Greenness under Water Balance in Different Desert Areas over the Silk Road Economic Belt

The sustainability of dryland vegetation growth over the Silk Road Economic Belt is under threat of water shortage, and the determination of water carrying capacity for vegetation is critically essential to balance water supply and water demand for the maintenance of existing ecosystems. To better understand how and why vegetation growth varies in different desert areas, this study first analyzed the spatiotemporal variation of the normalized difference vegetation index (NDVI). Then, we investigated the relationship between NDVI and climatic factors (precipitation, soil water content, air temperature, evapotranspiration), and estimated the threshold NDVI under water balance in different desert areas. Results showed that the higher NDVI was mainly distributed in Kazakhstan, Russia, and Azerbaijan, and it increased in approximately 53% of desert areas from 1982 to 2015 in the whole study region. The mean annual NDVI showed a simultaneous increasing trend in all desert areas from 1982 to 1994, and decreased significantly only in the cold arid desert area (p < 0.01, −0.0067 decade−1) or had no significant change in other desert areas after 1994 (p > 0.01). The climate condition generally appeared as a warming and drying trend in the past 34 years, with varied changing rates in different desert areas. NDVI presented a strong positive relationship with both precipitation and evapotranspiration in most desert areas. The threshold values of the mean annual NDVI under water balance between 1982 and 2015 were approximately 0.1041 (hot arid desert), 0.1337 (cold arid desert), 0.1346 (cold arid semi-desert), 0.0951 (hot arid desert semi-desert), 0.0776 (polar desert tundra), 0.1071 (hot arid desert shrub), 0.1377 (cold arid desert steppe), and 0.0701 (polar desert steppe), respectively. The responses of these threshold values to precipitation were all positive in different desert areas. These results provide an enhanced understanding of vegetation dynamics and ecological conservation, which are of great importance to implementing adaptation and mitigation measures for terrestrial ecosystems over the Silk Road Economic Belt.

Green Cimahi watershed for balancing water supply and flood control

Lack and damage of clean water and also flooding occurred in Cimahi river basin. Water sources polluted by industry and human activities. The purpose of this study was to design the water balance model of the Cimahi watershed as a Green Watershed. The study locations were the Cimahi river, Cilember river, Cibeureum river and Cisangkan river, which flow through the city of Cimahi. The method used is the analysis of the rainfall runoff model with the hydrograph of convolution method in the four watersheds, land use analysis, runoff coefficient analysis, dilution model analysis, groundwater analysis and demographic analysis. The results of this study is Design Green Cimahi Watershed that re-functioning local drainage to maintain the hydrological storage capacity of all watersheds in the city of Cimahi, normalizing Cilember river to reach the width of the river by 5.6 m from the previous width of 1.5 m, and the river capacity which was 4.8 m3 / s to 42.37 m3 / s so that enough to accommodate Q50 flood discharge, enforcing the rule that every industry must process its waste through a waste processing plant, building Pasirkaliki retention ponds that can function for groundwater conservation, flood control and clean water needs.

Adjustments of leaf traits and whole plant leaf area for balancing water supply and demand in Robinia pseudoacacia under different precipitation conditions on the Loess Plateau

The adjustments of plant traits for balancing water supply and demand are critical for keeping the survival of forests under drought stress. In this study, we aimed to determine the long-term adjustments of leaf traits and whole plant leaf area (PLA) in Robinia pseudoacacia trees under different precipitation conditions, and to provide physiological information for modelling. We characterized the temporal changes of plant traits with simulated different precipitation conditions using three levels of water supply in a controlled growth chamber. The results indicated that increasing transpiration with R. pseudoacacia growth leaded to a decline in soil moisture under each precipitation conditions. As drought progressed, leaves exhibited a coordinated increase in vein and stomatal densities, higher drought tolerance by increasing cell wall elasticity, and higher water storage capacitance. After 60 days, leaf traits were similar among the treatments while PLA decreased considerably with decreasing water supply. The field observation along a precipitation gradient indicated that PLA decreased by 64% as mean annual precipitation declined from 645.9 mm to 421.9 mm, while leaf traits did not exhibit marked differences among different sites. The variation in PLA along the precipitation gradient could be well estimated with the optimal PLA calculated by long-term simulations of soil water balance. In summary, increasing transpiration with plant growth induced similar patterns of soil desiccation under different precipitation conditions, which further resulted in the convergence in leaf traits. The adjustment of PLA achieved an optimal value to maximize plant growth and to prevent severe drought stress by balancing the water supply and demand. These results provided a way to fill the gap between experiments and modelling studies for large-scale predictions of plant traits, and should be helpful for the sustainable management of plantation forests in the Loess Plateau.