High Water Stress Research Articles

Gender inequality in global water security

Abstract Ensuring universal and equitable access to water and sanitation for all by 2030 (United Nations Agenda 2030, Sustainable Development Goal or SDG 6) is one of the most important goals for the world. 785 million people do not still have access to basic drinking water services. This burden disproportionately affects women, who are often responsible for collecting water from distant sources in regions with limited or no water supply systems. Understanding the spatial patterns of socio-demographic and hydrological factors is key to address the interlinked challenges of gender equality and water security under SDG 5 (‘Achieve gender equality’) and SDG 6. While the challenges women face in securing water are widely recognized, quantitative analysis of gender inequality in global water security has not previously been studied. Here, we present, to our knowledge the first global assessment of gender inequality in water security. We measured water security by examining both water access and water scarcity (hereafter, water stress), incorporating population data for working-age individuals and children. We integrated this hydrological and demographic information at a spatial resolution of approximately 10 km from 2000 to 2014 when the information is available. Our results showed that more working-age women than men experience poor water access, particularly in Africa. In addition, women in countries with high water insecurity, defined as high water stress and poor water access—such as Burkina Faso, Togo, and Somalia—primary conduct water collection. Our results indicate significant gender-based differences in water security, with women frequently remaining in rural areas characterized by poor water access. These inequalities could be further intensified by climate change and socio-economic factors.

Towards strategic interventions for global food security in 2050

This study aims to explore global food security, focusing on major cereal crops across different Agroecological Zones (AEZs). By projecting cereal production under different Shared Socioeconomic Pathways, insights into the challenges for achieving global food security by 2050 are drawn. The study identifies ‘critical’ risks in countries like Chad, Sudan, Algeria, Somalia, and Namibia in Africa, parts of Central Asia and the Middle East (Saudi Arabia), western USA, and Australia, due to high water stress combined with severe production deficits. However, implementing strategic interventions, like increasing harvested area, can significantly reduce these risks, potentially leading to surplus production in some regions. The regions still under cereal production deficit with such mitigation strategies are categorized in terms of risk to food security, considering water stress and import dependency. Iran, Venezuela, Sub-Saharan Africa, Saudi Arabia, parts of Southeastern Asia are projected to face persistent cereal production deficits and high import dependency by the mid-20th century. The study underlines the necessity for water-saving technologies and effective governance to balance crop production and water use, particularly in regions experiencing water scarcity.

Sustainable Water Resource Planning for Alanda Micro Watershed Using Geospatial Techniques

Groundwater is a vital natural resource, especially in areas lacking surface water bodies. About one-third of the global population relies on it for drinking, irrigation and industrial purposes. However, excessive and unregulated exploitation has led to a rapid decline in water tables, emphasizing the need for sustainable groundwater management. The Alanda micro watershed in Barshitakli Taluka, Akola District, Maharashtra, spans 11.39 km², with a sub-humid climate and uneven monsoon rainfall averaging 780 mm. The region faces high water stress in summer, with dried bore wells and farmers relying on rain and groundwater for irrigation. The water resource development plan for Alanda micro watersheds integrates GIS, remote sensing and AHP to identify groundwater potential zones. The Alanda micro watershed soil and water conservation plans were developed using GIS, remote sensing and the AHP method. Thematic maps were overlaid in ArcGIS, applying weighted factors from a pairwise comparison matrix to identify groundwater potential zones. These zones, categorised as high, moderate and low potential, highlight that the largest area has moderate potential, suggesting good opportunities for conservation measures. The survey of the study area identified existing soil and water conservation structures, including 3 farm ponds, 1 check dam and a contour bund. Additional recommendations include 5 farm ponds, 4 check dams, contour trenches and bunding measures, along with agronomic practices for effective surface and groundwater management.

The Integral Management of the Wastewater Treatment Sector in Mexico Using a Circular Economy Approach

Wastewater treatment must be proactive and sustainable to facilitate an increase in the circularity of water. Therefore, the current approach, based on a linear cycle, must be replaced with a circular economy concept that implements strategies to address the different byproducts in the wastewater treatment sector. In recent years, Nuevo León, Mexico, has encountered high water stress levels, with its main water bodies presenting their lowest levels ever recorded. This study was focused on the wastewater treatment plant Monterrey, which treats the largest volume at the state level. Throughout its operation process, it generates different potential byproducts that are yet to be harnessed to fully. This study developed three proposals using a circular economy approach: the treatment of water for the industrial sector, the use of residual sludge as an organic fertilizer, and the cogeneration of energy from biogas. These proposals can potentially generate benefits regarding the three pillars of sustainability, yielding a closed cycle in the wastewater treatment sector at the national level.

Siting Analysis of a Solar-Nuclear-Desalination Integrated Energy System

Nuclear power is typically deployed as a baseload generator. Increased penetration of variable renewables motivates combining nuclear and renewable technologies into Integrated Energy Systems (IES) to improve dispatchability, component synergies and, through cogeneration, address multiple markets. However, combining multiple energy resources heavily depends on the proper selection of each system’s location and design limitations. In this paper, co-siting options for IES that couple nuclear and concentrating solar power (CSP) with thermal desalination are investigated. A comprehensive siting analysis is performed that utilizes global information survey data to determine possible co-siting options for nuclear and solar thermal generation in the United States. Viable co-siting options are distributed across the Southwestern U.S., with the greatest concentration of siting options in the southern Great Plains, although siting with higher solar direct normal irradiance is possible in other states such as Arizona and New Mexico. Brackish water desalination is also attractive across the southwest U.S. due to high water stress, but for brackish water desalination reverse osmosis (an electricity driven process) is most cost- and energy-efficient, which does not require co-siting with the thermal generator. The most attractive state for nuclear and thermal desalination (which is more attractive when using seawater) is Texas, although other areas may become attractive as water stress increases over the coming decades. Co-siting of all CSP and thermal desalination is challenging as attractive CSP sites are not coastal.

KUFRI DAKSH: A NEW WATER-USE EFFICIENT TABLE POTATO VARIETY WITH CROSS TOLERANCE TO HIGH TEMPERATURE STRESS

Kufri (K) Daksh is a main season, medium maturing, high yielding, water-use-efficient table potato variety that can be grown in regions with limited water availability. It is a clonal selection from the cross between CP1748, having high water use efficiency and LT-1 tolerating high temperature stress. Its plants are tall and vigorous with field resistance to late blight. Its tubers are white-cream (light yellow), ovoid with shallow to medium eyes and cream flesh with good keeping quality. It is fertilizer responsive and can yield 30-35 t/ha under low water (≤ 20%) availability in middle Gangetic plains. K Daksh has better trade-off for high CO2 gain and low water loss through optimization in plant canopy leaf area and plant height components. K Daksh can be an excellent choice to tolerate high temperature and water stress regimes in changing climatic scenarios.

Influence of Anatomical Spatial Architecture of Pinus devoniana on Pressure Gradients Inferred from Coupling Three-Dimensional CT Imaging and Numerical Flow Simulations

Conifer forests in Michoacán are facing climate change. Pinus devoniana Lindley, with natural distribution in the state, has shown certain adaptability, and knowing the influence of anatomy in the flow system is essential to delimit how it contributes to safety margins and water efficiency. For this, the pressure gradients in the cell lumens and their ramifications were analyzed by numerical simulations of flow throughout the real microstructure. Xylem were evaluated in radial, tangential and longitudinal directions. With the skeletonization of lumens and their constrictions, a branching system of interconnection between tracheids, ray cells, intercellular chambers, extensions, and blind pits were identified. In the simulation, the branched system bypasses the longitudinal fluid passage through the pores in membranes of pairs of pits to redirect it through the direct path branching, contributing to safety margins and water efficiency. Thus, resilience at low pressures because of the lower pressure drop in the extensions. The interface between the branching system and the cell lumens are sites of higher pressure gradient, more conducive to water-vapor formation or air leakage in the face of the lowest pressure system. The flow lines move along easy paths, regardless of the simulated flow direction. Deposits in the cell extensions were shown to be attached to the S3 layer of the cell wall, leaving the center of the duct free to flow. It is concluded that the spatial architecture of the xylem anatomy of Pinus dvoniana is a factor in the resilience at low pressures due to high water stress of the species.

Hydrological and Urban Analysis of Territories under High Water Stress: Nazas and Aguanaval Rivers, Mexico

Hydrological region 36 in Mexico (RH36) faces significant water stress and tends towards agricultural mono-production. Following the regulation of its main rivers, the Nazas and Aguanaval, through dam construction and canalization, the flow of water in the lower basin of the Nazas River has become negligible, which has altered the riverfronts of major cities in the region. Consequently, Torreón, Gómez Palacio, and Lerdo, which are part of the La Laguna Metropolitan Zone (ZML), have expanded into new territories along the riverbanks and adjacent recharge areas. Establishing the boundaries of specific watersheds is crucial for the implementation of targeted rural and urban intervention strategies. This approach enhances understanding of interactions between the natural hydromorphology of a hydrological region, water infrastructure (dams, canals, reservoirs), and the urban and rural landscape. To effectively plan based on watershed boundaries, it is essential to develop hybrid cartographies that integrate urban, architectural, agricultural, and hydrological delineations. These maps provide valuable indicators for watershed-based planning, which facilitates precise hydrological urban restoration strategies tailored to specific basins. This research focuses on developing and presenting such hybrid cartographies, which combine hydrological, rural, and geographic data. This methodology aligns with the overarching objective of mitigating water stress in RH36 and promoting a transition towards more sustainable forms of agriculture.

Effects of High Salinity and Water Stress on Wetland Grasses from the Spanish Mediterranean Coast.

The impacts of climate change are reaching unprecedented levels, heightening the risk of species loss and ecosystem service degradation. Wetlands, highly threatened ecosystems, serve vital ecological functions by capturing carbon, filtering water, and harbouring diverse wildlife. Coastal wetlands encounter many challenges, such as increased drought periods and escalating salinity levels, severely impacting plant biodiversity. Assessing how plants respond to various environmental stress factors is imperative for devising successful conservation strategies. In the present study, we examined three representative grass species found in various habitats within the Albufera Natural Park, close to the city of Valencia on the Spanish Mediterranean coast: Imperata cylindrica, Phragmites australis, and Saccharum ravennae. High salinity and water stress conditions were induced by subjecting the plants to irrigation with solutions containing 200, 400, 600, and 800 mM NaCl or withholding irrigation altogether to mimic coastal flooding and drought scenarios. The treatments were maintained until noticeable wilting of the plants occurred, at which point a range of stress biomarkers were determined, including photosynthetic pigments, ions, osmolytes, oxidative stress markers, and antioxidant metabolites, as well as antioxidant enzyme activities. Saccharum ravennae displayed the highest sensitivity to salt stress, whereas I. cylindrica appeared to be the most tolerant. The primary salinity tolerance mechanism observed in I. cylindrica and P. australis was a blockage of ion transport from the root zone to the aerial part, together with the salt-induced accumulation of proline and soluble sugars to high concentrations in the former. No significant effects of the water deficit treatment on the growth or biochemical parameters were observed for any of the analysed species. These findings offer valuable information for the effective management and conservation of coastal wetlands facing the challenges posed by climate change.

Impacts of geopolitics and policy on Latin American biodiversity and water resources

AbstractLatin America is a major agricultural producer with important natural resources. Efforts have been made to protect sensitive areas but are hindered by agricultural trade disruptions outside the control of individual countries due to globally integrated crop markets. This analysis assesses the effects of two trade shocks, that is, the war in Ukraine and vehicle decarbonization in the United States (US), on biodiversity and water resources in Latin America. Results show that an increase in maize and wheat exports from the region triggered by the war in Ukraine negatively affects biodiversity in Brazil and leads to cropland expansion into drought‐prone areas in Argentina and Chile. For the case of reduced crop exports from Latin America due to US vehicle decarbonization and the corresponding shift away from US maize ethanol, the pressure on arable land in areas of high biodiversity and water stress is eased. As opposed to agricultural carbon emissions, which have global impacts, biodiversity and water issues have a strong local and regional significance. Regulatory frameworks aiming to protect these regions should be forward looking to detect and shield vulnerable areas from future threats. Other changes affecting global agriculture and trade, for example, sustainable aviation fuels in the US or the European Farm‐to‐Fork policy, need to be anticipated for effective policies in Latin America [EconLit Citations: Q13, Q25, Q34, Q56].

Normalised difference moisture index in water stress assessment of maize crops

Remote sensing is a promising technique for better management of water resources in agriculture through improvement of dynamic control and operational scheduling on irrigated croplands. The main goal of this study was to identify the possibilities of application of the normalised difference moisture index (NDMI) to water stress monitoring in maize crops, and to determine the relationship between the index and soil moisture content. The study was carried out in 2019–2021 in the experimental fields of disturbed maize, cultivated on dark-chestnut soils in the Southern Ukraine at the NAAS Institute of Climate-Smart Agriculture. The crop cultivation technology was common for the conditions of the steppe zone of Ukraine. Actual soil moisture content was determined by gravimetric method in the pre-sowing and post-harvest period. The NDMI values were calculated using cloudless aerospace images from the satellites Landsat 8, Sentinel-2, and MODIS with 250 m resolution. It was revealed that the seasonal NDMI dynamics perfectly reflected the water-supply conditions of the disturbed maize, and could be used for operational monitoring and scheduling of irrigation. The parameters of the water-supply conditions were determined in 2021, which was the wettest year of the study: the cumulative seasonal NDMI reached 1.71, while the highest water stress was recorded in the driest year, 2020, – the cumulative NDMI was 0.15. Additionally, there was a moderately strong negative correlation between NDMI and soil moisture content, and the coefficient of determination was 0.62. The linear regression models, developed to predict soil moisture content in the 0–100 cm layer depending on the NDMI values, had good fitting quality and reasonable accuracy, but they required further calibration and extension of the initial dataset to provide more robust and reliable results for practical implementation. Based on the results of the study, spatial NDMI could be considered a good and reliable tool for improving irrigation water management. Further studies should focus on the practical implementation of the NDMI-based model of moisture-content estimation, as well as on the possibilities of the index usage for mapping irrigated lands.

Reinforcement learning for watershed and aquifer management: a nationwide view in the country of Mexico with emphasis in Baja California Sur

Reinforcement Learning (RL) is a method that teaches agents to make informed decisions in diverse environments through trial and error, aiming to maximize a reward function and discover the optimal Q-learning function for decision-making. In this study, we apply RL to a rule-based water management simulation, utilizing a deep learning approach for the Q-learning value function. The trained RL model can learn from the environment and make real-time decisions. Our approach offers an unbiased method for analyzing complex watershed scenarios, providing a reward function as an analytical metric while optimizing decision-making time. Overall, this work underscores RL’s potential in addressing complex problems, demanding exploration, sequential decision-making, and continuous learning. External variables such as policy shifts, which are not readily integrated into the model, can substantially influence outcomes. Upon establishing a model with the requisite minimal states and actions, the subsequent learning process is relatively straightforward, depending on the selection of appropriate RL model algorithms. Its application depends on the specific problem. The primary challenge in this modeling approach lies in model definition, specifically in devising agents and actions that apply to complex scenarios. Our specific example was designed to address recent decision-making challenges related to constructing dams due to water scarcity. We present two examples: one from a nationwide perspective in Mexico and the other focused on Baja California Sur, the state with the highest water stress. Our results demonstrate our capability to prioritize watersheds effectively for the most significant benefits, particularly dam construction.

Geospatial distribution of qanats in middle eastern countries: Potential for sustainable groundwater system

Serious concerns have arisen regarding the depletion of groundwater aquifers and water shortage, particularly in the Middle East. The utilization of qanat, subterranean tunnel-wells, may serve as a solution to addressing water scarcity and present targeted strategies toward sustainable groundwater management. This research presents an analysis of the spatial distribution of active qanats in Afghanistan, Iran, Iraq, and Syria, considering the annual rainfall rate, the elevation from sea level, water stress risks, and groundwater table decline. It aims to identify the qanat sites that may be maintained and utilized. The findings reveal distinct geographical clusters of qanats, with a concentration in mountainous regions characterized by consistently high elevations ranging from 1500 to 2500 m above sea level and annual rainfall rates between 200 and 300 mm. In contrast, a more sporadic presence is observed in low-lying plains with elevations ranging from sea level to 1000 m, where the annual rainfall ranges between 300 and 600 mm. Participation in the restoration, maintenance, and utilization of qanats in regions facing high water stress and the risk of groundwater table decline, such as the central plateau of Iran, may offer a sustainable solution to water risk challenges.

Trajectory in water scarcity and potential water savings benefits in the Yellow River basin

Water scarcity caused by the mismatched spatiotemporal characteristics of water demand and supply threatens the sustainable development of many countries around the world. The Yellow River is the second largest river in China but suffers from intense human activity and scarce water resources. Most current studies on water scarcity assessment have coarse spatial and temporal resolution or are based over short periods, which precludes our understanding of the long-term trajectories of water scarcity. Moreover, the water savings potential and implications for water scarcity alleviation have not been well understood. Here, we conducted a comprehensive analysis of water scarcity in the Yellow River basin (YRB) during the period 1965–2013 using a survey-based water withdrawal dataset and water availability simulated by a well-validated hydrological model. Our results showed that regional water stress has continuously increased over the past five decades and has exceeded the threshold above which both ecological and socio-economic water resources are unsustainable since the 1990 s. Regions with high water stress were mostly distributed between the Lanzhou and Toudaoguai hydrological stations where large irrigated districts occur. There were 30.1–34.7 % and 20.2–35.5 % of the total population suffered from seasonal and perennial water scarcity, respectively, during different periods. Increased water withdrawal and population growth were the primary factors that caused changes in the exposure of the population to water scarcity. Meanwhile, we found that in the absence of upstream water consumption, water scarcity could be alleviated or removed for 4–13.2 % of the downstream population, especially during seasons when water is scarce (e.g., spring and winter). Water efficiency improvements could save 10.1 % of the total water usage (3.3 km3), of which a 7.8 % saving could come from irrigation, roughly 3.4 times the potential saving from industry (2.3 %). Irrigation savings can increase industrial added value by 4 %, while industrial water savings can meet the localized domestic water use of 4 % of urban, or 10 % of rural residents in sub-basins without water scarcity. These findings provide a basis for the design of measures to alleviate water scarcity and facilitate sustainable water resource management in the YRB.

HOUSEHOLD WATER INSECURITY EXPERIENCES (HWISE) SCALE: THE PROTOCOL OF CULTURAL ADAPTATION AND STATISTICAL VALIDATION

Annually Sri Lanka experiences substantial rainfall; but, the availability of water within the island nation is unbalanced. Lack of an appropriate system view, suitable national-level policy, and bimodal rainfall have resulted in Sri Lankans experiencing medium to high water stress. Considering the impact individual households have to endure due to the unavailability of water, the following study presents a protocol to culturally adapt and statistically validate the Household Water Insecurity Experiences (HWISE) scale to the Sinhala language. The protocol critically discusses the application of classical test theory (CTT) and item response theory (IRT) and documents all relevant steps for the scale validation process. Through this study protocol, the authors attempt to demonstrate the procedural rigor of the adaptation and validation process of the HWISE scale to the Sinhala language in Sri Lanka. The availability of a valid scale to evaluate household water insecurity experiences will assist public health experts, policymakers, and the government in understanding the nature and severity of water stress and the consequences across health, economic, and psychosocial contexts. Similarly, preventative interventions and key policies could be implemented to further support the initiatives of responsible authorities.<p> </p><p><strong> Article visualizations:</strong></p><p><img src="/-counters-/soc/0758/a.php" alt="Hit counter" /></p>

Pro-environmental behaviour in household water use. A gender perspective

Efficiency in the use of water resources is one of the SDG 6 in all sectors. This research focuses on the efficient use of water in households. Specifically, we analyse differences in people’s behaviour towards ten household water uses. Compared to previous research, the main contribution of this study is the emphasis placed on the gender perspective. This research is carried out for Andalusia, a region in southern Spain with high water stress. OLS and probit estimations were made with a database of 2650 observations from 2018. No gender differences are found in the number of habits applied to make efficient use of water in the household. On the other hand, after studying ten household water uses in isolation, gender differences are found in certain pro-environmental habits. We cannot conclude the existence of a gender gap in environmental awareness of water use. However, the results suggest that there are differences in the adoption of pro-environmental habits in water use due to the distribution in the household chores, especially in those which are traditionally female or male.

Assessing the spatial variation of water poverty determinants in Maharashtra, India

Abstract Water scarcity is an emerging multidimensional issue concerning not only the physical availability of resources but also is linked with poverty. The existing literature has established a relationship between income poverty and water poverty. In the Indian context, various studies have explored such issues using the Water Poverty Index (WPI), but only a few have analyzed downscale spatial units. This paper constructs district-level water poverty measures and maps its spatial heterogeneity for Maharashtra, India. Using an indicator-based approach, we aggregate various dimensions of water poverty into a single index. This composite index is formulated by normalizing the indicators and assigning weights using principal component analysis. After rescaling, the aggregate WPI score varies from 0 to 1, denoting lower to higher water poverty. The overall WPI estimate of Maharashtra is 0.47, implying high water stress. The study presents district-wise WPI information by combining the results with Geographic Information System (GIS). Our findings suggest that along with the physical abundance and accessibility to water, improvement in the determinants of capacity and environment is essential to tackle water poverty. Results highlight the intra-district variations among components of water poverty, indicating the importance of local-scale policy-making for better water resource management.

Obtaining Spatial Variations in Cabernet Sauvignon (Vitis vinifera L.) Wine Flavonoid Composition and Aromatic Profiles by Studying Long-Term Plant Water Status in Hyper-Arid Seasons

The spatial variability in vineyard soil might negatively affect wine composition, leading to inhomogeneous flavonoid composition and aromatic profiles. In this study, we investigated the spatial variability in wine chemical composition in a Cabernet Sauvignon (Vitis vinifera L.) vineyard in 2019 and 2020. Because of the tight relationships with soil profiles, mid-day stem water potential integrals (Ψstem Int) were used to delineate the vineyard into two zones, including Zone 1 with relatively higher water stress and Zone 2 with relatively lower water stress. Wine from Zone 2 generally had more anthocyanins in 2019. In 2020, Zone 1 had more anthocyanins and flavonols. Zone 2 had more proanthocyanidin extension and terminal subunits as well as total proanthocyanidins in 2020. According to the Principal Component Analyses (PCA) for berry and wine chemical composition, the two zones were significantly different in the studied wine aromatic compounds. In conclusion, this study provides evidence of the possibility of managing the spatial variability of both wine flavonoid composition and aromatic profiles through connecting vineyard soil variability to grapevine season-long water status.

The specialized parenchyma in the Paspalum vaginatum stem as a strategy to water deficit and salinity

Abstract Paspalum vaginatumis a halophyte plant found along coastal plains, which presents cells with atypically thickened walls in the ground tissue of the stem stele (GTS). The tolerance of this species to high salinity and water stress led us to investigate whether the thickened walls could be related to adaptation to the coastal environment. Thus, we sought to characterize the cell walls that make up the GTS ofP. vaginatum, describe the tissue, and verify the influence of the water resource on the thickening of the walls and a possible function related to the reserve of substances. For this, analyses were carried out using light microscopy, transmission electronic microscopy, and histochemical tests. The samples were collected in the field during low and high rainfall periods.Paspalum vaginatumGTS cells have pectic-cellulosic primary walls. In most basal internodes, these cells presented thickened walls formed in two to three layers. Statistical analysis demonstrated that the level of precipitation is directly related to cell wall thickening. The data suggest the storage and mobilization of substances through the cell wall of the specialized parenchyma.

Magnetized Seeds and Structured Water: Effects on Resilience of Velvet Bean Seedlings (Mucuna pruriens) under Deficit Irrigation

A custom-built water generator supplied structured water (SW) for applying the deficit irrigation treatments to velvet bean plants (Mucuns pruriens). The objectives of the study were to 1) determine the effects of magnetized seed treatment on velvet bean plants, 2) determine the effects of magnetized and hydroxylated water treatments on velvet bean plants, and 4) determine the effects of deficit irrigation, using three soil moisture levels, on velvet bean plants. The optimal water-saving treatment was magnetized seeds plus 10 MT + HWT. This treatment had a 226% increase in transpiration and a 22% increase in water vapor concentration in the intercellular airspace for the low soil moisture watering schedule. The three study factors in the optimal seed and water treatment had a synchronistic effect for enhancing metabolic efficiency by increasing whole plant WUE by 87% and carbon assimilation efficiency by 66% in the low soil moisture schedule. Plants irrigated with SW water and grown from magnetized seeds had enhanced resilience to high water stress conditions by maintaining adequate levels of biologically structured water. The rapid deactivation of a suite of highly interconnected defense activities in the optimal seed and water treatments implies that the plants exhibit macroscopic coherence properties. Coherence at the macroscopic level resulted in complex synchronization between metabolic efficiency, plant health, and deactivation of a suite of regulatory defenses in plants exposed to high water stress.