Controversy over the Use of “Shade Covers” to Avoid Water Evaporation in Water Reservoirs

Abstract

Water scarcity and sustainability are main current concerns affecting billions of people worldwide. Apart from policies designed to guarantee water supply, technologies and procedures have been developed to optimize the uses of water and water recycling as well as to minimize water scarcity. Among these technologies, those based on the use of bioinspired fibres, membranes, nanomaterials, liquid-liquid extraction methods using ionic liquids or approaches involving plants or microbes have been successfully carried out. One of the main problems associated with most of these technologies is the high cost of their implementation and maintenance. Consequently, other cheaper strategies have been explored, such as the use of shade covers. The objective of this work is to summarize the most recent findings on the use of shade covers (suspended shade cloth covers and shade objects) on water reservoirs, mainly agricultural water reservoirs (AWRs). Reflections on the investment-benefit relationship of this technological proposal are also herein discussed. Apart from traditional shade cloth clover, more recently, other covers like shade balls/squares/hexagons (shady objects) have also been proposed as promising approaches to save water and keep its quality. However, the manufacturing of shady objects, mainly made of polyethylene plastic, results in: (i) high cost (high energy cost and use of raw materials like crude oil and natural gas); (ii) significant production of residues, and (iii) visual environmental pollution. The main conclusion reached from this review is that the controversy over the use of shade covers continues in the spotlight of scientists, water managers, and related companies; although this approach saves water and prevents water quality deterioration, a large number of recalcitrant residues are produced, not only during their production, but also when they must be replaced due to deterioration.

Impounding Reservoirs, Benefits and Risks: A Review of Environmental and Technical Aspects of Construction and Operation

“…R5-No update of water management instructions. R6-Possible negative impact on the morphology of the watercourse and the region downstream of the dam cross-section C2.2-Climate change impacts [53][54][55][56][57][58][59][60] The analyses concern 2 very large and 6 large reservoirs in Asia, 4 large reservoirs in Europe and a large reservoir system in South America. In addition, in [56] the reservoir capacity was a variable value, and in [60] a review based on a large dataset was performed.…”

“…The development of new technologies to technically reduce evaporation from storage tanks is also noticeable. However, studies have indicated that shade covers are not universally and widely applicable due to the high energy and water consumption in the production process, which translates into a high cost of implementing such a solution [60].…”

“…Sustainability 2023, 15, x FOR PEER REVIEW 8 of 23 future decades is not accurately recognised, and, moreover, its intensity is closely linked to a particular region of the Earth. In the publications analysed [57][58][59][60], there were discrepancies in the estimation of the magnitude of changes in temperature and precipitation, as well as different conclusions regarding the amount of evaporation. The paper [58] found a significant correlation between an increase in atmospheric CO2 concentration and a decrease in average evapotranspiration, while other studies indicated a general increase in water loss from reservoirs due to evaporation [57].…”

“…At the planning stage: Estimating design parameters based on climate models and catchment development changes [49,56]. Reducing evaporation through "shade curtains" when economically justified [60,122].…”

Evaporative loss and environmental impact of covers on water storages: A review

“…Modular floating covers were first designed to prevent water bird access to water storages close to airport runways (“bird balls,” Martinez‐Espinosa, 2021). Some municipal water managers adopted the strategy to reduce evaporative loss, which in the case of Los Angeles in the USA involved the release of 96 million 100 mm in diameter, high‐density polyethylene balls over the 175 acre water surface of the reservoir (Kavanaugh, 2016).…”