Shortest-Path-Based Two-Phase Design Model for Hydraulically Efficient Water Distribution Network: Preparing for Extreme Changes in Water Availability

Grasslands, covering over 40% of terrestrial land surfaces, play a critical role in regional water cycling through their greening processes. However, the decoupling mechanisms between grassland greening and water availability (WA) changes across the Northern Hemisphere, along with their future trajectories, remain poorly understood. Here, we integrated multi-source satellite observations with CMIP6 model ensembles to systematically assess the spatiotemporal evolution and trend divergence of leaf area index (LAI) and WA across Northern Hemisphere grasslands from 2000 to 2100. Our results showed that grassland LAI exhibited sustained growth during 2000–2020, with 55.28% of regions showing significant increasing trends. However, 73.67% of grassland regions experienced declining WA during the historical period, revealing widespread decoupling between grassland greening and water deficit. Future scenario projections indicated a reversal to increasing WA trends, with 57.51% of regions showing significant increases under SSP5–8.5. Furthermore, 61.87% of grasslands exhibited greening-driven drying (GDD) characteristics during the historical period, while greening-driven wetting (GDW) regions were projected to expand to 72.44% in the future. Analysis along aridity gradients revealed that humid zones contributed most prominently to LAI and WA changes. Mechanistic decomposition demonstrated that grassland WA changes shifted from precipitation-dominated control (53.60%) in the historical period toward a regime jointly governed by precipitation dominance and coupled precipitation–evapotranspiration drivers in the future. Concurrently, the dominant factor controlling grassland greening transitioned from vapor-pressure deficit (VPD) to temperature (TEM) control. Additionally, driving factors exhibited pronounced differentiation patterns along aridity gradients during the historical phase: arid zones were dominated by soil moisture (SM) and semi-arid zones displayed dual control by SM and VPD, while humid zones were governed by coupled TEM-VPD regulation. This study reveals the divergent trends between grassland greening and WA and unravels their driving mechanisms, offering important scientific evidence for formulating regionally differentiated ecological water resource management strategies.

Dryland communities find little refuge from grazing due to long-term changes in water availability

The avocado cv. Hass requires a suitable rootstock for optimal development under water stress. This study evaluated the performance of two avocado rootstocks (ANRR88 and ANGI52) grafted onto cv. Hass under four water stress conditions, 50% and 25% deficit, and 50% and 25% excess during the nursery stage. Plant height, leaf area (LA), dry matter (DM), and Carbon (OC) content in the roots, stems, and leaves were measured. Root traits were evaluated using digital imaging, and three vegetation indices (NDVI, CIRE, and MTCI) were used to quantify stress. The results showed that genotype significantly influenced the response to water stress. ANRR88 exhibited adaptation to moderate to high water deficits. ANGI52 adapted better to both water deficit and excess, and showed greater root exploration. LA and DM reductions of up to 60% were observed in ANRR88, suggesting a higher sensitivity to extreme changes in water availability. More than 90% of the total OC accumulation was observed in the stem and roots. The NDVI and the MTCI quantified the presence and levels of stress applied, and the 720 nm band provided high precision and speed for detecting stress. These insights are crucial for selecting rootstocks that ensure optimal performance under varying water availability, enhancing productivity and sustainability.

The broad objective of this study is to estimate the economic impact of changes in water availability due to climate change in Switzerland with a 2050 time horizon. To do so, the sectoral structure of the computable general equilibrium model GEMINI-E3 is being extended. Raw water resources are introduced as a production factor into the model and a drinking water distribution sector is specified for Switzerland to allow for a precise analysis of the economic consequences of restricted water supply. Predictions of water availability in 2050 are taken from a hydrological model and alternative climate change scenarios are considered. Simulations show possible restrictions in water resource availability to increase raw water prices substantially compared to the baseline. However, the global economic impact for Switzerland is rather small due to the low price of raw water in Switzerland and its small value in the benchmark scenario. Finally, the simulation of scenarios featuring alternative levels of endogenous adaptive capacity of the economy highlights the importance of the ability to reduce water losses and to transform production processes to decrease their water intensity in determining the extent of welfare losses provoked by a decrease in water availability.

Hydraulic performance benchmarking for effective management of water distribution networks: An innovative composite index-based approach

Strengthening the planning of hydrological resources to optimize the use of water in agriculture is a key adaptation measure of the Chilean agricultural sector to cope with future climate change. To address this challenge, decision-makers call for tools capable of representing farmers’ behaviours under the likely stresses generated by future climate conditions. In this context, of special concern are the effects of water variability on small-scale farmers, who commonly operate with narrow profit margins and who lack access to financial resources and technological knowledge. This paper sheds light on the economic impacts of changes in water availability on small-scale agriculture. We provide a hydro-economic modelling framework that captures the socio-economic effects of water shocks on smallholders in the Vergara River Basin, Chile. This approach links a farm risk-based economic optimization model to a hydrologic simulation model adjusted for the basin. Our results indicate that at the aggregated level, there will be minor economic impacts of climate change on the basin’s small-scale agriculture, with small decreases in both expected utility and wealth. However, large differences in the economic impacts of wealthy and poor small-scale farmers are found. Changes in water availability, reduce the options of land reallocation to increase farmer’s expected utility, being the poor small-scale farmers the most negatively affected.

This study presents an innovative data-driven approach to optimally design water distribution networks (WDNs). The methodology comprises five key stages: Generation of 600 synthetic WDNs with diverse properties, optimized to determine optimal component diameters; Extraction of 80 topological and hydraulic features from the optimized WDNs using graph theory; preprocessing and preparing the extracted features using established data science methods; Application of six feature selection methods (Variance Threshold, k-best, chi-squared, Light Gradient-Boosting Machine, Permutation, and Extreme Gradient Boosting) to identify the most relevant features for describing optimal diameters; and Integration of the selected features with four machine learning models (Random Forest, Support Vector Machine, Bootstrap Aggregating, and Light Gradient-Boosting Machine), resulting in 24 ensemble models. The Extreme Gradient Boosting-Light Gradient-Boosting Machine (Xg-LGB) model emerged as the optimal choice, achieving R2, MAE, and RMSE values of 0.98, 0.017, and 0.02, respectively. When applied to a benchmark WDN, this model accurately predicted optimal diameters, with R2, MAE, and RMSE values of 0.94, 0.054, and 0.06, respectively. These results highlight the developed model’s potential for the accurate and efficient optimal design of WDNs.

The current and future water availability for Mediterranean basins was assessed under different climate and policy scenarios. The high-resolution GIS-based WAPA model (Water Availability and Adaptation Policy Analysis) was used to obtain potential water availability under a set of realistic hypotheses. Diverse data sets were compiled on meteorological variables, water resources, runoff, land cover, and population density to create a geospatial database that covers river basins that drain into the Mediterranean Sea. The model was forced with the results of the global hydrological models H08 and CWatM for ISIMIP (Inter-Sectoral Impact Model Intercomparison Project) scenarios. These two hydrological models were forced with climate drivers for three historical scenarios (obsclim, picontrol, and historical), which define a baseline, and three future scenarios (ssp126, ssp370 and ssp585) provided by the sixth assessment report of IPCC (2023). A high-resolution map of the potential availability of water for irrigation was developed in Mediterranean basins. The allocation of water for irrigation is subordinated to the urban supply (drinking water) and for the conservation of river ecosystems. The results indicate that changes in hydrological regimes across the region are expected to have a significant impact on future water availability. The proposed approach provides a valuable tool for decision makers and stakeholders for the identification of areas vulnerable to changes in water availability. The information generated in this study, high-resolution spatial outputs and detailed water availability estimates, could work as a relevant input for integrated water resource management and climate change adaptation planning. This research offers a robust framework for assessing water resources under changing climate, applicable to other regions facing similar challenges. In summary, our study provides useful information to policymakers and stakeholders, helping them to make informed decisions to develop adaptive measures for sustainable water management under uncertain future climate conditions.

Epiphytes are highly dependent on atmospheric inputs of water and nutrients. Reductions in water availability associated with warming and climate change and continual atmospheric nitrogen (N) deposition can affect plant growth but few studies have evaluated the effects of changes in both water and nutrient availabilities on epiphytes. We experimentally tested whether epiphyte growth is more water- or nutrient-limited, if nutrient limitation was stronger for nitrogen or phosphorus, and whether nutrient limitation interacts with water availability. We applied watering (high and low) and nutrient addition (control, +N, +P, +N+P) treatments to greenhouse-grown Asplenium nidus, a common epiphytic fern found in many tropical and subtropical wet forests. We measured leaf area production and leaf elemental concentrations to assess how A. nidus growth and physiology respond to changes in water and nutrient availabilities. We found that leaf growth of A. nidus was more affected by water availability than nutrient addition and the effect of adding nutrients was not fully realized under low-water availability. Among the different nutrient treatments, +N+P had the greatest effects on A. nidus growth and physiology in both watering treatments. Watering treatment changed leaf elemental concentrations but not their ratios (i.e. C:N and N:P). Nutrient addition altered C:N and N:P ratios and increased the concentration of the added elements in leaves, with more pronounced increases in the high-watering treatment. We conclude that the growth of A. nidus is more water- than nutrient-limited. When nutrient limitation occurs (i.e. under high-water availability), nutrient co-limitation is stronger than limitation by N or P alone. This result taken together with studies of other epiphytes suggests greater water than nutrient limitation is likely widespread among epiphytic plants. The limited effects of nutrient addition in the low-water treatment suggest that the effect of atmospheric N deposition on epiphyte growth will be limited when water availability is low.

Sensitivity analysis to assess the relative importance of pipes in water distribution networks

The aim of this research is to support the assessment of countries’ risks of water conflicts in the immediate future, considering their vulnerability to changes in water availability. The risk of international water conflicts in the 5 years ahead of the year of analysis was estimated based on current water availability and its unequal distribution. Countries were classified by their vulnerability to reductions in water availability. In these vulnerability groups, the links of water availability (TRIP discharges per capita) and its unequal distribution with the risk of water conflicts were explored. The Gini Coefficient was employed to measure the inequalities. Inequalities showed statistically significant positive Logit links with the risk of water conflicts. The greatest risk for volatile conflicts exists for the Asian, South American and African countries, having the lowest water availability and the lowest economic capacity. Increasing inequalities increases the likelihood of water conflicts, suggesting enhancing access to water, to lower the likelihood of water conflicts. South American and Congo River basin countries are only at risk of low-level water conflicts, but have higher risks of conflict escalation, when inequality increases. The risk of North American and Asian water conflicts were modeled well, except in western Asia. The water conflict estimation provided only 11.9 % under-estimations and an accuracy of 54.1 %, globally. Inequalities in water can indicate the risk of water conflicts in the above regions. However, the risk of water conflicts between countries with higher economic capacity in the European continent showed no link with inequality. This study will facilitate the estimation of the risk of water conflicts resulting from climate change.

The Murray-Darling Basin in south-eastern Australia is one of the world’s largest rivers, draining an area of just over 1 million square kilometres. The basin drains about one-seventh of the Australian land mass and is the 16th longest river in the world. However, being located on the driest continent on Earth, its discharge is relatively small, averaging just 767 m3/s, far smaller than the discharge from any other similarly sized river worldwide.Despite the relative lack of water, the Murray-Darling Basin is one of the most significant agricultural areas in Australia. In 2008, the Murray-Darling Basin Authority was formed with a mandate to manage the basin in an integrated and sustainable manner. Water reform in the basin has been a world-first in terms of the scale of intervention, but it has led to numerous conflicts in terms of access to water. The ability to manage the basin adequately relies on appropriate research being carried out in order to determine how much water is currently available, where it is currently being used, and how water availability and use are likely to change into the future.Climate change projections for the Murray-Darling Basin indicate a future that is likely to be hotter, with more frequent and intense droughts, accompanied by a reduction in cool season rainfall, particularly in the south of the Basin. As this is where the majority of runoff is generated, this is likely to lead to reductions in water availability, with a median reduction of around 20%.The Murray-Darling Basin Plan was brought into force in 2012 and is due for review in 2026. CSIRO is carrying out hydroclimate research to assist policy makers to better understand the likely changes in water availability, and consequent adaptation options available to them. This presentation will summarise the likely climate change impacts on water availability and assess how best to deal with the uncertainties associated with these projections.

KEY-WORDS: Bolivia, drought tolerance, shade tolerance, functional traits, trade-offs, ecophysiology, species distribution Tropical forests occur under rainfall regimes that vary greatly in the rainfall pattern and frequency and intensity of drought. Consequently water availability is one of the most important environmental factors influencing community structure, species composition, and plant functioning across large-scale rainfall gradients and small-scale topographic gradients within forests. The relative success of tree species to establish along these gradients of water availability and their success in dealing with future changes in water availability will depend on how they are adapted to tolerate drought. In this dissertation I applied a multi-species, multi-trait approach in field studies and a controlled experiment to give detailed information on the mechanisms of drought-tolerance of a large set of tropical dry and moist forest tree species. The following research questions were addressed; 1) How do dry and moist forests differ in soil water availability? 2) How are dry and moist forest species adapted to drought and what different drought-strategies can be distinguished? 3) Is there a trade-off between drought- and shade-tolerance? and 4) How do drought- and shade-tolerance determine local and regional tree species distribution? Dry season soil water availability is clearly lower in the dry forest than in the moist forest. Especially in the dry forest there is a lot of temporal and spatial variation in soil water availability. Temporal variation depends on the annual cycle of precipitation. Spatial heterogeneity is two-dimensional; 1) water availability varies with topography of the landscape; elevated crests are dry in comparison to slopes and low valleys, and 2) soil water is vertically redistributed with soil depth; in the dry season more water is available in deep soil layers while in the wet season most water is found in the top soil. When combining temporal and spatial dimensions, a complex mosaic of soil water availability emerges that shows great potential for niche partitioning among species at various levels, if species are adapted to exploit this variation. Seedlings of dry forest species have evolved mechanisms that enhance their access to water in deep soil layers, increase drought-induced cavitation resistance and increase water conservation. Seedlings of moist forest species show adaptations that improve their light foraging capacity and increase nutrient and water acquisition. Associations among functional traits show that there are three major drought strategies among tropical tree species, 1) physiological drought-tolerance, 2) drought-intolerance and 3) drought-avoidance. No conclusive evidence for a direct trade-off between species drought- and shade-tolerance was found, and the association between drought- and shade-tolerance is mainly subject to the scale of observation. On small scales, within the dry forest, drought- and shade-tolerance are positively related, as species hydraulic properties are integrally linked with niche differentiation for both light and water. This implies that in their distribution, light-demanding species will be restricted to habitats that combine high light and high moisture availability, while shade-tolerant species will be the better competitors in drier and shadier habitats. On larger scales a strong trade-off between above and belowground biomass allocation was found, which should in theory have resulted in a trade-off between drought- and shade-tolerance, but in practice it did not. Plants can compensate for a low root mass fraction by producing relatively cheap roots with a large specific root length and compensate for a low leaf mass fraction by making cheap leaves with a large specific leaf area. Drought- and shade-tolerance thus depend largely on different suites of morphological traits and can be uncoupled. Species distribution along the rainfall gradient was not directly explained by species drought survival, mainly because deciduousness was the most important factor contributing to survival and deciduous species are well represented in both dry and moist forests. The occurrence of evergreen species at the dry end of the rainfall gradient largely depends on drought related traits as a high wood density and a large biomass allocation to deep roots. Species occurrence at the moist end of the rainfall gradient was mainly determined by traits related to light-demand, as a high leaf mass fraction and long, branched root systems. In conclusion, I propose that at small scales, within forests, species distribution along water gradients depends on the interaction between species drought- and shade-tolerance while at larger scales distribution of (evergreen) species is mainly determined by their drought-tolerance.

Soils are important sources and sinks of three greenhouse gases (GHGs): carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). However, it is unknown whether semiarid landscapes are important contributors to global fluxes of these gases, partly because our mechanistic understanding of soil GHG fluxes is largely derived from more humid ecosystems. We designed this study with the objective of identifying the important soil physical and biogeochemical controls on soil GHG fluxes in semiarid soils by observing seasonal changes in soil GHG fluxes across a three million year substrate age gradient in northern Arizona. We also manipulated soil nitrogen (N) and phosphorus availability with 7 years of fertilization and used regression tree analysis to identify drivers of unfertilized and fertilized soil GHG fluxes. Similar to humid ecosystems, soil N2O flux was correlated with changes in N and water availability and soil CO2 efflux was correlated with changes in water availability and temperature. Soil CH4 uptake was greatest in relatively colder and wetter soils. While fertilization had few direct effects on soil CH4 flux, soil nitrate was an important predictor of soil CH4 uptake in unfertilized soils and soil ammonium was an important predictor of soil CH4 uptake in fertilized soil. Like in humid ecosystems, N gas loss via nitrification or denitrification appears to increase with increases in N and water availability during ecosystem development. Our results suggest that, with some exceptions, the drivers of soil GHG fluxes in semiarid ecosystems are often similar to those observed in more humid ecosystems.

Abstract. From the analysis of rainfall data available at about 5000 stations, this paper is prepared to provide comprehensive assessment of water availability in different states of India as well as for the country as a whole. Changes in water availability per person are occurring mainly as a consequence of changes in population. The water availability per capita in India was over 6000 m3 per annum in 1951, it now stands at about 1900 m3 per capita. Nevertheless, this amount is nearly twice the water need by the people of developed countries. The developed countries require about 1000 m3 of freshwater per capita per year. The increasing demand for water is in the 4 states of Haryana, UP, Bihar and West Bengal in the face of increasing population and possible changes in climate, the water available in these states is to be used most economically and judiciously so that the vagaries of nature do not put any severe strain.