Sustainable irrigation and climate feedbacks

Agricultural irrigation induces greenhouse gas emissions directly from soils or indirectly through the use of energy or construction of dams and irrigation infrastructure, while climate change affects irrigation demand, water availability and the greenhouse gas intensity of irrigation energy. Here, we present a scoping review to elaborate on these irrigation-climate linkages by synthesizing knowledge across different fields, emphasizing the growing role climate change may have in driving future irrigation expansion and reinforcing some of the positive feedbacks. This Review underscores the urgent need to promote and adopt sustainable irrigation, especially in regions dominated by strong, positive feedbacks.

Heat exposure during outdoor activities in the US varies significantly by city, demography, and activity

Environmental heat is a growing public health concern in cities. Urbanization and global climate change threaten to exacerbate heat as an already significant environmental cause of human morbidity and mortality. Despite increasing risk, very little is known regarding determinants of outdoor urban heat exposure. To provide additional evidence for building community and national-scale resilience to extreme heat, we assess how US outdoor urban heat exposure varies by city, demography, and activity. We estimate outdoor urban heat exposure by pairing individual-level data from the American Time Use Survey (2004-2015) with corresponding meteorological data for 50 of the largest metropolitan statistical areas in the US. We also assess the intersection of activity intensity and heat exposure by pairing metabolic intensities with individual-level time-use data. We model an empirical relationship between demographic indicators and daily heat exposure with controls for spatiotemporal factors. We find higher outdoor heat exposure among the elderly and low-income individuals, and lower outdoor heat exposure in females, young adults, and those identifying as Black race. Traveling, lawn and garden care, and recreation are the most common outdoor activities to contribute to heat exposure. We also find individuals in cities with the most extreme temperatures do not necessarily have the highest outdoor heat exposure. The findings reveal large contrasts in outdoor heat exposure between different cities, demographic groups, and activities. Resolving the interplay between exposure, sensitivity, adaptive capacity, and behavior as determinants of heat-health risk will require advances in observational and modeling tools, especially at the individual scale.

Water Distribution System Failure Risks with Increasing Temperatures

In the coming decades, ambient temperature increase from climate change threatens to reduce not only the availability of water but also the operational reliability of engineered water systems. Relatively little is known about how temperature stress can increasingly cause hardware components to fail, quality to be affected, and service outages to occur. Changes to the estimated-time-to-failure of major water system hardware and the probability of quality noncompliance were estimated for a modern potable water system that experiences hot summer temperatures, similar to Phoenix, AZ, and Las Vegas, NV. A fault tree model was developed to estimate the probability that consequential service outages in quantity and quality will occur. Component failures are projected to have a percent increase of 10-101% in scenarios where peak summer temperature has increased from 36 to 44 °C, which create the conditions for service outages to have a percent increase of 7-91%. Increased service outages due to multiple pumping unit failures and water quality noncompliances are the most notable concerns for water utilities. The most effective strategies to prevent temperature-related failures should focus on monitoring and correcting chlorine residual and disinfection byproduct concentration, and on cooling pumping unit motors and electronics.

Energy efficiency to reduce residential electricity and natural gas use under climate change

Climate change could significantly affect consumer demand for energy in buildings, as changing temperatures may alter heating and cooling loads. Warming climates could also lead to the increased adoption and use of cooling technologies in buildings. We assess residential electricity and natural gas demand in Los Angeles, California under multiple climate change projections and investigate the potential for energy efficiency to offset increased demand. We calibrate residential energy use against metered data, accounting for differences in building materials and appliances. Under temperature increases, we find that without policy intervention, residential electricity demand could increase by as much as 41-87% between 2020 and 2060. However, aggressive policies aimed at upgrading heating/cooling systems and appliances could result in electricity use increases as low as 28%, potentially avoiding the installation of new generation capacity. We therefore recommend aggressive energy efficiency, in combination with low-carbon generation sources, to offset projected increases in residential energy demand.

Spatial Differences and Costs of Emissions at U.S. Airport Hubs

As local governments plan to expand airport infrastructure and build air service, monetized estimates of damages from air pollution are important for balancing environmental impacts. While it is well-known that aircraft emissions near airports directly affect nearby populations, it is less clear how the airport-specific aircraft operations and impacts result in monetized damages to human health and the environment. We model aircraft and ground support equipment emissions at major U.S. airports and estimate the monetized human health and environmental damages of near airport (within 60 miles) emissions. County-specific unit damage costs for PM, SOx, NOx, and VOCs and damage valuations for CO and CO2 are used along with aircraft emissions estimations at airports to determine impacts. We find that near-airport emissions at major U.S. airports caused a total of $1.9 billion in damages in 2013, with airports contributing between $720 thousand and $190 million each. These damages vary by airport from $1 to $9 per seat per one-way flight and costs per passenger are often greater than airport charges levied on airlines for infrastructure use. As the U.S. aviation system grows, it is possible to minimize human and environmental costs by shifting aircraft technologies and expanding service into airports where fewer impacts are likely to occur.

Improving the accuracy of vehicle emissions profiles for urban transportation greenhouse gas and air pollution inventories

Metropolitan greenhouse gas and air emissions inventories can better account for the variability in vehicle movement, fleet composition, and infrastructure that exists within and between regions, to develop more accurate information for environmental goals. With emerging access to high quality data, new methods are needed for informing transportation emissions assessment practitioners of the relevant vehicle and infrastructure characteristics that should be prioritized in modeling to improve the accuracy of inventories. The sensitivity of light and heavy-duty vehicle greenhouse gas (GHG) and conventional air pollutant (CAP) emissions to speed, weight, age, and roadway gradient are examined with second-by-second velocity profiles on freeway and arterial roads under free-flow and congestion scenarios. By creating upper and lower bounds for each factor, the potential variability which could exist in transportation emissions assessments is estimated. When comparing the effects of changes in these characteristics across U.S. cities against average characteristics of the U.S. fleet and infrastructure, significant variability in emissions is found to exist. GHGs from light-duty vehicles could vary by -2%-11% and CAP by -47%-228% when compared to the baseline. For heavy-duty vehicles, the variability is -21%-55% and -32%-174%, respectively. The results show that cities should more aggressively pursue the integration of emerging big data into regional transportation emissions modeling, and the integration of these data is likely to impact GHG and CAP inventories and how aggressively policies should be implemented to meet reductions. A web-tool is developed to aide cities in improving emissions uncertainty.

Intertemporal cumulative radiative forcing effects of photovoltaic deployments

Current policies accelerating photovoltaics (PV) deployments are motivated by environmental goals, including reducing greenhouse gas (GHG) emissions by displacing electricity generated from fossil-fuels. Existing practice assesses environmental benefits on a net life-cycle basis, where displaced GHG emissions offset those generated during PV production. However, this approach does not consider that the environmental costs of GHG release during production are incurred early, while environmental benefits accrue later. Thus, where policy targets suggest meeting GHG reduction goals established by a certain date, rapid PV deployment may have counterintuitive, albeit temporary, undesired consequences. On a cumulative radiative forcing (CRF) basis, the environmental improvements attributable to PV might be realized much later than is currently understood, particularly when PV manufacturing utilizes GHG-intensive energy sources (e.g., coal), but deployment occurs in areas with less GHG-intensive electricity sources (e.g., hydroelectric). This paper details a dynamic CRF model to examine the intertemporal warming impacts of PV deployments in California and Wyoming. CRF payback times are longer than GHG payback times by 6-12 years in California and 6-11 years in Wyoming depending on the PV technology mix and deployment strategy. For the same PV capacity being deployed, early installations yield greater CRF benefits (calculated over 10 and 25 years) than installations occurring later in time. Further, CRF benefits are maximized when PV technologies with the lowest manufacturing GHG footprint (cadmium telluride) are deployed in locations with the most GHG-intensive grids (i.e., Wyoming).

The conservation nexus: valuing interdependent water and energy savings in Arizona

Water and energy resources are intrinsically linked, yet they are managed separately--even in the water-scarce American southwest. This study develops a spatially explicit model of water-energy interdependencies in Arizona and assesses the potential for cobeneficial conservation programs. The interdependent benefits of investments in eight conservation strategies are assessed within the context of legislated renewable energy portfolio and energy efficiency standards. The cobenefits of conservation are found to be significant. Water conservation policies have the potential to reduce statewide electricity demand by 0.82-3.1%, satisfying 4.1-16% of the state's mandated energy-efficiency standard. Adoption of energy-efficiency measures and renewable generation portfolios can reduce nonagricultural water demand by 1.9-15%. These conservation cobenefits are typically not included in conservation plans or benefit-cost analyses. Many cobenefits offer negative costs of saved water and energy, indicating that these measures provide water and energy savings at no net cost. Because ranges of costs and savings for water-energy conservation measures are somewhat uncertain, future studies should investigate the cobenefits of individual conservation strategies in detail. Although this study focuses on Arizona, the analysis can be extended elsewhere as renewable portfolio and energy efficiency standards become more common nationally and internationally.

Integrating life-cycle environmental and economic assessment with transportation and land use planning

The environmental outcomes of urban form changes should couple life-cycle and behavioral assessment methods to better understand urban sustainability policy outcomes. Using Phoenix, Arizona light rail as a case study, an integrated transportation and land use life-cycle assessment (ITLU-LCA) framework is developed to assess the changes to energy consumption and air emissions from transit-oriented neighborhood designs. Residential travel, commercial travel, and building energy use are included and the framework integrates household behavior change assessment to explore the environmental and economic outcomes of policies that affect infrastructure. The results show that upfront environmental and economic investments are needed (through more energy-intense building materials for high-density structures) to produce long run benefits in reduced building energy use and automobile travel. The annualized life-cycle benefits of transit-oriented developments in Phoenix can range from 1.7 to 230 Gg CO2e depending on the aggressiveness of residential density. Midpoint impact stressors for respiratory effects and photochemical smog formation are also assessed and can be reduced by 1.2-170 Mg PM10e and 41-5200 Mg O3e annually. These benefits will come at an additional construction cost of up to $410 million resulting in a cost of avoided CO2e at $16-29 and household cost savings.