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Dam reservoirs are at the core of local water storage and supply, especially in water-stressed regions of the world with acute water shortage problems. However, evaporative losses from these reservoirs and their storage efficiency are often overlooked in water budgeting. We offer a mechanistic approach that combines physically-based modeling with remote sensing information of reservoir characteristics to reliably predict evaporative losses from dam reservoirs. The developed framework is used to predict evaporative water losses from potential dam reservoirs in different basins worldwide. We apply this framework to 10 of the largest dam reservoirs in the world's water-stressed regions to quantify evaporative water losses. Our analysis, spanning from 2000 to 2020, reveals considerable variations in annual evaporation rates in the reservoirs located in water-deprived regions exceeding 3200 mm/year during the study period with the total evaporative loss reaching 26.5 km3/year. The evaporative water loss accounts up to 15.8% of the storage capacity in one of the dam reservoirs, posing significant challenges for water allocation and conservation strategies, with notable economic and environmental consequences in regions already suffering from water scarcity. • A mechanistic framework was developed to quantify evaporation from dam reservoirs. • Evaporation accounts for up to 15.8% of the storage capacity of the dam reservoirs in water-stressed regions. • The study improves water accounting and management in regions with acute water scarcity. [ABSTRACT FROM AUTHOR]

Increasing demand for freshwater in arid regions with chronic water shortage calls for expansion of water storage for drought periods while protecting storage from evaporative losses. A cost‐effective and scalable method for evaporation suppression uses floating elements; however, little is known regarding biochemical and water quality effects under these covers. Two identical reservoirs with area of 25 m2 and depth of 2 m were used to investigate the influence of floating covers on water quality parameters for a period of one year (2019–2020). One of the reservoirs was covered with Styrofoam discs, and results were compared with the uncovered one. Results showed that the evaporation suppression efficiency of floating discs gradually decreased from 80% in spring to about 60% in winter. The comparison between reservoirs revealed that the presence of floating covers decreased pH, electrical conductivity (EC), total dissolved solids (TDS) and dissolved oxygen by 11%, 11%, 15% and 36%, respectively. We observed an increase in nitrate (30%), phosphate (27%) and ammonia (95%) concentrations in the covered reservoir. Results also demonstrated more concentration of biological populations such as algae and protozoa in the uncovered reservoir. The findings highlight improvement of certain water quality parameters in covered reservoirs such as EC and TDS with potential impacts on irrigation systems and soil health and salinity constraints. [ABSTRACT FROM AUTHOR]

Evaporative losses from reservoirs exacerbate water shortage during dry spells. Notwithstanding the extensive application of self-assembling floating covers for suppressing evaporation, the cover material is often overlooked and limited to available choices such as plastics. The present study is aimed at the production of floating covers using ultra-lightweight alkali-activated slag concrete that offers a range of mechanical and chemical features. Concrete specimens were made with different percentages of ground granulated blast-furnace slag as the binder, sodium metasilicate as the alkaline activator and lightweight perlite aggregates with a density of 100–150 kg/m3. To solve the problem of fracture in the preliminary specimens, slag was partially replaced with 15, 20 and 30% lime. In addition, microsilica (10, 12 and 15%) was introduced to improve the mechanical properties of the samples. In designs without microsilica, 30% replacement of slag with lime resulted in the desirable density, strength and permeability of samples. Results showed that microsilica generally increased the density, resistance and thermal conductivity of samples by 7, 74 and 14%, respectively, while water absorption and permeability decreased by 15% and 14%, respectively. The dry density of samples was obtained between 340 and 516 kg/m3 with a compressive strength of 0.2–0.9 MPa and a conductive heat transfer coefficient of 0.067–0.093 W/mK. [ABSTRACT FROM AUTHOR]

Water reservoirs have been used to mitigate seasonal water shortages since the dawn of civilization. Present day use of water reservoirs continues to expand to meet the increasing demand for irrigation water and to mitigate effects of climate change and droughts. Losses to evaporation are an important challenge to water storage efficiency in arid regions. We study the use and efficiency of self‐assembling floating covers as a simple and scalable solution to evaporation suppression. We report laboratory‐scale studies of evaporation suppression using different cover types under various external conditions that jointly affect surface flux partitioning. Experiments using floating spheres and disks of different colors, sizes, and materials were conducted for a range of external conditions (radiation, wind, and wind + radiation) over a 1.44 m2 water basin placed in a wind tunnel. Considering maximum cover density using spherical and disk‐shaped elements (91% surface cover), the evaporation was suppressed by 80% (for disks) and 70% (for spheres) relative to uncovered water surfaces in agreement with physically based model estimates. Surprisingly, evaporation suppression using black and white floating covers was similar despite significantly different surface energy partitioning pathways. The observed similarity was attributed to thermal decoupling between the top of cover elements and water surfaces. The study shows a high and nearly constant evaporation suppression efficiency of floating covers for a range of external conditions supporting the potential of such simple and scalable solution of evaporation suppression for regions with limited infrastructure or alternative water solutions. Key Points: Evaporative water losses from reservoirs in arid regions can be reduced effectively by floating coversIn a lab‐scale study on the effect of floating covers on water evaporation we found that 70‐80% of evaporation could be suppressedBlack and white covers had similar evaporation fluxes, due to the decoupling of energy partitioning of the covers from the water surface [ABSTRACT FROM AUTHOR]