Improving regional water scarcity footprint characterization factors of an available water remaining (AWARE) method

Impact of the Grain for Green Project on water resources and ecological water stress in the Yanhe River Basin

The Grain for Green project (GGP), initialized by the Chinese government in 1999, has achieved substantial achievements accompanied by a decrease in surface runoff on the Loess Plateau, but the impacts of large-scale afforestation on regional water resources are uncertain. Hence, the objective of this study was to explore the impact of land use change on generalized water resources and ecological water stress using the blue and green water concepts, taking the Yanhe River Basin as the case study. The Soil and Water Assessment Tool (SWAT) was applied to quantify the green water and blue water, which are defined as generalized water resources. The ecological water requirement of vegetation (forest and grass), agricultural water footprint and virtual water flow are considered regional water requirements. The land use types of 1980 (Scenario I) and 2017 (Scenario II) were entered into the SWAT model while keeping the other parameters constant to isolate the influence of land use changes. The results show that the average annual differences in blue, green and generalized water resources were -72.08 million m³, 24.34 million m³, and -47.74 million m³, respectively, when the simulation results of Scenario II were subtracted from those of Scenario I, which shows that land use change caused by the GGP led to a decrease in blue and generalized water resources and an increase in green water resources. Surface runoff in Scenario I was more than that in Scenario II in all of the years of the study period from 1980–2017, and green water storage in Scenario I was more than that in Scenario II in all of the years of the study period except in 1998; although lateral flow in Scenario I was less than that in Scenario II except in 2000 and 2015, as was groundwater runoff in 1992, 2000 and 2015, and green water flow in 1998. Blue water flow, green water storage and green water flow in Scenario II were less than those in Scenario I in the whole basin, 12.89 percent of the basin and 99.21 percent of the basin, respectively. The total water footprint increased from 1995 to 2010 because the forest water footprint increased significantly in this period, although the agricultural water footprint and grass water footprint decreased. The ecological water stress index values had no obvious temporal change trends in either land use scenario, but the ecological water stress index in Scenario II was greater than that in Scenario I, which illustrates that the GGP led to an increase in ecological water stress from the perspective of generalized water resources.

Improving water scarcity footprint capabilities in arid regions through expansion of characterization factor methods

Water scarcity footprint (WSF) is a recent addition to life cycle assessment methodology that has advanced the understanding of freshwater environmental impact. The Available Water Remaining (AWARE) method is one approach that has gained significant traction in WSF applications. While an effective method for determining WSF, the methodology has limitations that constrain capabilities for determining freshwater environmental impact in arid regions. The primary limitation is the inability to compare regions when more water demand exists than what is available which typically occurs in arid regions. This limitation reduces resolution and therefore decision-making capabilities. This work proposes a novel method for determining WSF in arid regions by capturing and quantifying scarcity when water demand is greater than availability. The approach presented here, called the demand to availability (DTA) method, is intended to be used for small-scale, or subregion analyses in areas where truncation occurs using standard AWARE methods. With the regional specificity, unique characterization factors can be developed to enhance deterministic resolution and ultimately improve decision-making abilities. The DTA methods are presented universally, allowing for application and implementation to any region. A case study was developed to demonstrate the effectiveness of the DTA method by analyzing characterization factors (CFs) and alfalfa WSFs in the arid Southwestern United States. Using the standard AWARE methods, this region originally truncated 38% of counties resulting in zero resolution or decision-making abilities. Results of the case study that used the proposed DTA method show an improved resolution in 100% of these counties, both within CF and alfalfa WSF. Although the proposed method is an improvement for understanding WSFs in arid regions, limitations and constraints still exist and are discussed.

Polypyrrole-Dopamine Nanofiber Light-Trapping Coating for Efficient Solar Vapor Generation

Solar vapor generation (SVG) typically uses a solar absorbing material at the water-air interface to convert solar energy into heat for evaporation. However, the intrinsic solar absorption of the material determines the upper limit of the solar energy capture. By designing a light-trapping surface structure with open pores and channels, we can break this limit and further improve the absorption by enabling multiple reflections within the surface. Polypyrrole (PPy) is emerging as a promising solar thermal material. In this work, we propose an ultrasonic spray coating method to obtain a nanofiber light-trapping coating by copolymerization with dopamine (DA), which can be directly synthesized at room temperature rapidly (30 min). Due to its excellent wettability, this coating can transport water and can be directly coated on the thermal insulating layer, not requiring an additional water transport layer. This nanoscale coating significantly improves solar absorption at different incident angles across the full solar spectrum, achieving the highest solar-to-thermal conversion efficiency of 95.8% at 1.385 kg·m^-2·h^-1 under 1 sun. When applied on salt water, this solar evaporator achieves self-cleaning in the absence of solar irradiation. Moreover, the surface structure can be further tuned into granular/plane-fibrous/plane-granular structures by using different oxidants or surfactants, and their formation mechanisms are also proposed. This PPy-DA nanofiber coating shows great potential for SVG and other applications based on a PPy material, especially for those requiring a certain surface morphology.

Critical evaluation of functional aspects of evaporation barriers through environmental and economics lens for evaporation suppression - A review on milestones from improved technologies

Climate change models predict an increase in rainfall variability, leading to floods and drought events, hence intensifying the need for reservoirs. However, up to 50% of reservoirs' capacity is lost by evaporation, affecting their function of ensuring water availability and stability. Over decades biological, chemical and physical barriers "covers" were developed for inhibiting evaporation. Such barrier's efficiency and applicability are still a matter of discussion, given their economic efficiency, environmental consequences, and operational difficulties are accounted for. In this review, we discussed the efficiency, applicability, and environmental suitability of these covers. Compared to the physical covers, the chemical and biological solutions tend to be less efficient. However, the use of physical covers is multidisciplinary, involving climate, material, and hydrological sciences, and are more efficient. Among the physical covers, the use of suspended covers and free-floating elements decreases evaporation to the tune of 85 and 80.0%, respectively. However, the economic efficiency of free-floating elements remains an open question since all studies overlooked their water footprint (water used in the manufacturing process of these covers), which was found to be very high. The use of these covers decreases heat storage, gas exchange rate, and light availability that could adversely influence dissolved oxygen, water quality, aquatic organisms, and the water ecosystem's function. These ecological consequences have not yet been investigated. The exception is the suspended covers, which have had determinate effects on dissolved oxygen and algae growth. Due to light weight, floating elements' operation is unstable and vulnerable to move due to wind effects. Therefore, such covers must be engineered to increase their stability. Free-floating elements could provide a visible and scalable solution to evaporation suppression when considering their economic visibility, environmental effects, and stability against wind and wave effects under the field conditions. However, these covers can be viable only when water availability is the limiting factor in crop production. We found that studies at reservoir scale are highly limited, therefore, investigations at reservoirs' scale emphasizing ecological aspects, cover stability and cost efficiency, are urgently needed.

Assessing the water scarcity footprint of food crops by growing season available water remaining (AWARE) characterization factors in Thailand

Water scarcity problems are a national agenda that must be prioritized. Thailand is an agricultural country with agriculture consuming a large amount of water. Sustainable water management for the agricultural sector is urgently needed. This study assessed the impacts of water consumption by agricultural products using a water scarcity footprint (WSF) assessment. This study presents the use of the growing season available water remaining characterization factors (AWARE CFs) of specific crops, based on growth months of that crop, instead of the annual AWARE CFs of agricultural products to assess the value of this approach for an appropriate assessment of water resource and the planning of crop production priorities. The original marginal AWARE CF was considered for determining the growing season AWARE CFs of major rice, second rice, sugarcane, maize, and cassava in 25 Thai watersheds. The growing season AWARE CFs of the food crops were used to determine their WSFs for the 25 Thai watersheds. The growing season AWARE CFs of major rice, second rice, sugarcane, maize, and cassava for Thailand were 1.74, 11.5, 6.01, 3.28, and 7.96 m³ world-eq. per m³ consumed, respectively. There were statistical differences between the means of annual AWARE CFs and growing season AWARE CFs for all Thai food crops in almost all watersheds. The WSFs using growing season AWARE CFs of major rice, second rice, sugarcane, maize, and cassava were 0.05-3.66, 1.10-193, 0.51-7.99, 1.09-8.28, and 1.65-30.3 m³ world-eq. per kilogram, respectively. This work identified suitable watersheds for growing food crops and compiled them as databases for the use of zoning food crop cultivation by the Thai government. Regarding WSF values, the least suitable watershed for growing major rice, second rice, sugarcane, and cassava was the Petchaburi watershed. The least suitable watershed for growing maize was the Chao Phraya watershed.