A warming-induced reduction in snow fraction amplifies rainfall extremes.

The intensity of extreme precipitation events is projected to increase in a warmer climate1-5, posing a great challenge to water sustainability in natural and built environments. Of particular importance are rainfall (liquid precipitation) extremes owing to their instantaneous triggering of runoff and association with floods6, landslides7-9 and soil erosion10,11. However, so far, the body of literature on intensification of precipitation extremes has not examined the extremes of precipitation phase separately, namely liquid versus solid precipitation. Here we show that the increase in rainfall extremes in high-elevation regions of the Northern Hemisphere is amplified, averaging 15 per cent per degree Celsius of warming-double the rate expected from increases in atmospheric water vapour. We utilize both a climate reanalysis dataset and future model projections to show that the amplified increase is due to a warming-induced shift from snow to rain. Furthermore, we demonstrate that intermodel uncertainty in projections of rainfall extremes can be appreciably explained by changes in snow-rain partitioning (coefficient of determination 0.47). Our findings pinpoint high-altitude regions as 'hotspots' that are vulnerable to future risk of extreme-rainfall-related hazards, thereby requiring robust climate adaptation plans to alleviate potential risk. Moreover, our results offer a pathway towards reducing model uncertainty in projections of rainfall extremes.

Widespread woody plant use of water stored in bedrock.

In the past several decades, field studies have shown that woody plants can access substantial volumes of water from the pores and fractures of bedrock1-3. If, like soil moisture, bedrock water storage serves as an important source of plant-available water, then conceptual paradigms regarding water and carbon cycling may need to be revised to incorporate bedrock properties and processes4-6. Here we present a lower-bound estimate of the contribution of bedrock water storage to transpiration across the continental United States using distributed, publicly available datasets. Temporal and spatial patterns of bedrock water use across the continental United States indicate that woody plants extensively access bedrock water for transpiration. Plants across diverse climates and biomes access bedrock water routinely and not just during extreme drought conditions. On an annual basis in California, the volumes of bedrock water transpiration exceed the volumes of water stored in human-made reservoirs, and woody vegetation that accesses bedrock water accounts for over 50% of the aboveground carbon stocks in the state. Our findings indicate that plants commonly access rock moisture, as opposed to groundwater, from bedrock and that, like soil moisture, rock moisture is a critical component of terrestrial water and carbon cycling.

Water rights trading planning and its application in water resources management: A water-ecology-food nexus perspective.

Nexus approach provides an effective perspective for implementing synergetic management of water resources. In this study, an interval two-stage chance-constrained water rights trading planning model under water-ecology-food nexus perspective (ITCWR-WEF) is proposed to analyze the interaction between water trading and water-ecology-food (WEF) nexus, which fills in the water resources management gaps from a novel nexus perspective. ITCWR-WEF incorporates hydrological simulation with soil and water assessment tool (SWAT), water rights configuration with interval two-stage chance-constrained programming (ITCP), and multi-criterion analysis with Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS). The developed ITCWR-WEF is applied to a real case of Daguhe watershed, which has characteristics of water scarcity, food producing areas and fragile ecosystem. Initial water rights allocation is addressed before the trading. Mechanisms analysis is designed to reveal mutual effect of water rights trading and WEF nexus. Optimal water management scenario is identified through multi-criterion analysis. Results reveal that the mechanism of water rights trading with WEF nexus under low constraint-violation risk level of water availability and environment capacity is recommended to promote the rational water resources allocation to balance the economic goals, water environment and water supply security, as well as ecological and food water demand guarantees.

Peak grain forecasts for the US High Plains amid withering waters.

Irrigated agriculture contributes 40% of total global food production. In the US High Plains, which produces more than 50 million tons per year of grain, as much as 90% of irrigation originates from groundwater resources, including the Ogallala aquifer. In parts of the High Plains, groundwater resources are being depleted so rapidly that they are considered nonrenewable, compromising food security. When groundwater becomes scarce, groundwater withdrawals peak, causing a subsequent peak in crop production. Previous descriptions of finite natural resource depletion have utilized the Hubbert curve. By coupling the dynamics of groundwater pumping, recharge, and crop production, Hubbert-like curves emerge, responding to the linked variations in groundwater pumping and grain production. On a state level, this approach predicted when groundwater withdrawal and grain production peaked and the lag between them. The lags increased with the adoption of efficient irrigation practices and higher recharge rates. Results indicate that, in Texas, withdrawals peaked in 1966, followed by a peak in grain production 9 y later. After better irrigation technologies were adopted, the lag increased to 15 y from 1997 to 2012. In Kansas, where these technologies were employed concurrently with the rise of irrigated grain production, this lag was predicted to be 24 y starting in 1994. In Nebraska, grain production is projected to continue rising through 2050 because of high recharge rates. While Texas and Nebraska had equal irrigated output in 1975, by 2050, it is projected that Nebraska will have almost 10 times the groundwater-based production of Texas.

What Is Groundwater? How to Manage and Protect Groundwater Resources.

Among the water resources on earth, groundwater is a resource hidden in the rocks of the earth's crust. For various reasons, notably the fact that this water is not directly visible but also as a consequence of education and longstanding traditions, the properties and physical laws governing groundwater are not well known outside the circle of hydrogeologists, the scientists specialists of the survey, management, and protection of groundwater resources. This resource has lots of advantages, notably when compared to surface water, and is thus largely used worldwide for many purposes: agriculture, tap water, industries, bottling, etc. In fact, this resource is available year-long, even during the dry season and in arid countries, and is well protected from surface contaminations. It needs, however, to be appropriately managed and protected to ensure its sustainability (quantity and quality). Thus, this study intends to provide the basics of the groundwater science, "hydrogeology." It is illustrated by examples taken from the Evian Natural Mineral Water, that is groundwater, and the way it is managed and protected. The groundwater resource is a sustainable water resource belonging to the earth's water cycle, which flows thanks to the natural energy provided by the sun. The main physical processes of the groundwater water cycle are the infiltration of rainwater into the soil, its slow flow within the pervious rocks from the earth's crust, called "aquifers," and finally its natural outflow at springs and into rivers. It can also be reached with man-made wells and pumped. Groundwater contains dissolved minerals that are mostly the results of interactions between the water and the aquifers' rocks.

Will We Soon Run Out of Water?

In 2000, the World population was 6.2 billion; it reached 7 billion in 2012 and should reach 9.5 billion (±0.4) in 2050 and 11 billion (±1.5) in 2100, according to UN projections. The trend after 2100 is still one of global demographic growth, but after 2060, Africa would be the only continent where the population would still increase. The amount of water consumed annually to produce the food necessary to meet the needs varies greatly between countries, from about 600 to 2,500 m3/year per capita, depending on their wealth, their food habits (particularly meat consumption), and the percentage of food waste they generate. In 2000, the total food production was on the order of 3,300 million tons (in cereal equivalents). In 2019, about 0.8 billion inhabitants of the planet still suffer from hunger and do not get the nutrition they need to be in good health or, in the case of children, to grow properly (both physically and intellectually). Assuming a World average water consumption for food of 1,300 m3/year per capita in 2000, 1,400 m3/year in 2050, and 1,500 m3/year in 2100, a volume of water of around 8,200 km3/year was needed in 2000, 13,000 km3/year will be needed in 2050, and 16,500 km3/year in 2100. Will that much water be available on earth? Can there be conflicts related to a food deficit? Some preliminary answers and scenarios for food production will be given from a hydrologist viewpoint.

Finding water scarcity amid abundance using human-natural system models.

Water scarcity afflicts societies worldwide. Anticipating water shortages is vital because of water's indispensable role in social-ecological systems. But the challenge is daunting due to heterogeneity, feedbacks, and water's spatial-temporal sequencing throughout such systems. Regional system models with sufficient detail can help address this challenge. In our study, a detailed coupled human-natural system model of one such region identifies how climate change and socioeconomic growth will alter the availability and use of water in coming decades. Results demonstrate how water scarcity varies greatly across small distances and brief time periods, even in basins where water may be relatively abundant overall. Some of these results were unexpected and may appear counterintuitive to some observers. Key determinants of water scarcity are found to be the cost of transporting and storing water, society's institutions that circumscribe human choices, and the opportunity cost of water when alternative uses compete.

Organochlorine Pesticides and Potentially Toxic Elements in Groundwater from a Protected Reserve in the Maya Region of Hopelchen, Mexico.

Water quality degradation by organochlorine pesticides and potentially toxic elements is of worldwide concern. This research explores groundwater conditions, regarding organochlorine pesticides and potentially toxic elements, in Hopelchen, Campeche, which is located in the buffer zone of the Calakmul Biosphere Reserve. Unfortunately, agriculture is allowed and agrochemical use is not monitored and sanctioned. Results show that Heptachlor, Endosulfan, and Dieldrin, all recognized carcinogens, had concentrations above the Mexican normative recommended values. Conversely, Cd and Ni concentrations were below recommended values. These results demonstrate that government intervention involving immediate control over agrochemical use is mandatory. Also, the results underscore the contamination of groundwater in several of the Calakmul Biosphere Reserve's buffer zones by organochlorine pesticides concentrations, posing a probable threat for local inhabitants who consume this water and use it for recreation.

Toward a comprehensive explanatory model of reliance on alternatives to the tap: evidence from California's retail water stores.

Building on a recent increase in scholarly attention to the problem of tap water mistrust and resulting negative health impacts, we examine the relationship between neighborhood reliance on tap water alternatives and a range of explanatory factors. We model retail water store locations as a proxy for reliance on tap water alternatives in urbanized neighborhoods across California. Our study is unique in its inclusion of variables representing both compliance with primary and secondary water quality standards by publicly regulated drinking water systems serving particular neighborhoods, other water system attributes and the socioeconomic characteristics of neighborhoods. The location of retail water stores in urbanized neighborhoods does not appear strongly related to observed measures of water quality. Secondary contamination shows a weak relationship to tap alternative reliance, and primary contamination was not correlated with higher levels of tap alternative reliance. On the other hand, our research suggests that other socioeconomic factors, particularly country of birth, are associated with the prevalence of more water stores. Increasing reliance on tap water likely requires measuring and addressing secondary contamination found in distributional systems and premise plumbing, and more aggressive public education campaigns.

The future of WRRF modelling - outlook and challenges.

The wastewater industry is currently facing dramatic changes, shifting away from energy-intensive wastewater treatment towards low-energy, sustainable technologies capable of achieving energy positive operation and resource recovery. The latter will shift the focus of the wastewater industry to how one could manage and extract resources from the wastewater, as opposed to the conventional paradigm of treatment. Debatable questions arise: can the more complex models be calibrated, or will additional unknowns be introduced? After almost 30 years using well-known International Water Association (IWA) models, should the community move to other components, processes, or model structures like 'black box' models, computational fluid dynamics techniques, etc.? Can new data sources - e.g. on-line sensor data, chemical and molecular analyses, new analytical techniques, off-gas analysis - keep up with the increasing process complexity? Are different methods for data management, data reconciliation, and fault detection mature enough for coping with such a large amount of information? Are the available calibration techniques able to cope with such complex models? This paper describes the thoughts and opinions collected during the closing session of the 6th IWA/WEF Water Resource Recovery Modelling Seminar 2018. It presents a concerted and collective effort by individuals from many different sectors of the wastewater industry to offer past and present insights, as well as an outlook into the future of wastewater modelling.

Climate-environment-water: integrated and non-integrated approaches to reservoir operation.

Integrated water planning and management face multiple challenges, among which are the competing interests of several water-using sectors and changing climatic trends. This paper presents integrated and non-integrated climate-environment-water approaches for reservoir operation, illustrated with Karkhe reservoir, Iran. Reservoir operation objectives are meeting municipal, environmental, and agricultural water demands. Results show the integrated approach, which relies on multi-objective optimization of municipal, environmental, and agricultural water supply, improves the municipal, environmental, and agricultural objectives by 70, 32, and 65% compared with the objectives' values achieved with the non-integrated approach, which implements a standard operating policy.

A fuzzy multi-objective optimization approach for treated wastewater allocation.

In face of the new climate and socio-environmental conditions, conventional sources of water are no longer reliable to supply all water demands. Different alternatives are proposed to augment the conventional sources, including treated wastewater. Optimal and objective allocation of treated wastewater to different stakeholders through an optimization process that takes into account multiple objectives of the system, unlike the conventional ground and surface water resources, has been widely unexplored. This paper proposes a methodology to allocate treated wastewater, while observing the physical constraints of the system. A multi-objective optimization model (MOM) is utilized herein to identify the optimal solutions on the pareto front curve satisfying different objective functions. Fuzzy transformation method (FTM) is utilized to develop different fuzzy scenarios that account for potential uncertainties of the system. Non-dominated sorting genetic algorithm II (NSGA-II) is then expanded to include the confidence level of fuzzy parameters, and thereby several trade-off curves between objective functions are generated. Subsequently, the best solution on each trade-off curve is specified with preference ranking organization method for enrichment evaluation (PROMETHEE). Sensitivity analysis of criteria's weights in the PROMETHEE method indicates that the results are highly dependent on the weighting scenario, and hence weights should be carefully selected. We apply this framework to allocate projected treated wastewater in the planning horizon of 2031, which is expected to be produced by wastewater treatment plants in the eastern regions of Tehran province, Iran. Results revealed the efficiency of this methodology to obtain the most confident allocation strategy in the presence of uncertainties.

Assessing climate change impacts on water resources and crop yield: a case study of Varamin plain basin, Iran.

This research evaluated climate change impacts on water resources using soil and water assessment tool (SWAT) models under representative concentration pathway scenarios (RCP 2.6, RCP 6, RCP 8.5). First, drought intensity was calculated using the standardized precipitation index (SPI) for the period 1987-2016. Then, the coefficients of precipitation as well as minimum and maximum temperature changes were simulated as SWAT model inputs. The results revealed that temperature will rise in future periods and the precipitation rate will be changed consequently. Then, changes in runoff during periods of 2011-2040, 2041-2070, and 2071-2100 were simulated by introducing downscaled results to SWAT model. The model was calibrated and validated by SWAT calibration and uncertainty procedures (SWAT-CUP). Nash-Sutcliffe (NS) coefficients (0.57 and 0.54) and R2 determination coefficients (0.65 and 0.63) were obtained for calibration and validation periods, respectively. The results showed that runoff will rise in fall and spring while it will drop in winter and summer throughout future periods under all three scenarios. Such seasonal shifts in runoff levels result from climate change consequences in the forms of temperature rise, snowmelt, altered precipitation pattern, etc. Future-period evapotranspiration will rise under all three scenarios with a maximum increase in the period 2070-2100 under RCP 8.5 scenario. Additionally, rainfed crop yields will decline without considerable changes in irrigated and horticultural crop yields.

Numerical simulation to assess potential groundwater recharge and net groundwater use in a semi-arid region.

Accurate assessment of deep percolation (potential groundwater recharge) under different field crops is essential for sustainable management of scarce water resources and proper planning of crop rotation in irrigated, semi-arid regions of the world. The potential recharge from commonly grown field crops in semi-arid Indo-Gangetic Plain (IGP) of India was estimated using HYDRUS-1D model, where, irrigation, evapotranspiration, and soil moisture dynamics were simulated. Simultaneously, net groundwater use by different cropping patterns was also calculated. Among the hydraulic parameters, n was found most sensitive for water percolation. During rainy season, 293.8 and 159.1 mm water was percolated below the root zone of cotton and soybean, respectively, which accounted for 39.4 and 32.9% of the water input. During winter season, 66.8 and 30.3 mm water was percolated below the root zone of winter maize and mustard, respectively, accounting for 20.5 and 10.6% of added water. It was observed that net groundwater use was positive for cotton, soybean, and summer maize with the values of 168.8, 159.1, and 18.0 mm year-1, respectively, and negative for rice, wheat, winter maize, and mustard. For the eight most important cropping patterns of semi-arid IGP, the net groundwater use was negative and varied between - 4.4 mm year-1 for cotton-maize and -423 mm year-1 for rice-wheat. With these cropping patterns, the overall rate of decline of groundwater was 231 mm year-1. It was found that maize-wheat and soybean-wheat cropping patterns consume much less water than rice-wheat cropping pattern and therefore are suitable to arrest the declining trend of groundwater in semi-arid IGP of India.