Warming and Elevated CO2 Have Opposing Influences on Transpiration. Which is more Important?

Current Forestry Reports (Springer) | March 14th, 2018

Plant transpiration is a key component of the terrestrial water cycle, and it is important to understand whether rates are likely to increase or decrease in the

Plant transpiration is a key component of the terrestrial water cycle, and it is important to understand whether rates are likely to increase or decrease in the future. Plant transpiration rates are affected by biophysical factors, such as air temperature, vapour pressure deficits and net radiation, and by plant factors, such as canopy leaf area and stomatal conductance. Under future climate change, global temperature increases, and associated increases in vapour pressure deficits, will act to increase canopy transpiration rates. Increasing atmospheric CO2 concentrations, however, is likely to lead to some reduction in stomatal conductance, which will reduce canopy transpiration rates. The objective of the present paper was to quantitatively compare the importance of these opposing driving forces. First, we reviewed the existing literature and list a large range of observations of the extent of decreasing stomatal conductance with increasing CO2 concentrations. We considered observations ranging from short-term laboratory-based experiments with plants grown under different CO2 concentrations to studies of plants exposed to the naturally increasing atmospheric CO2 concentrations. Using these empirical observations of plant responses, and a set of well-tested biophysical relationships, we then estimated the net effect of the opposing influences of warming and CO2 concentration on transpiration rates. As specific cases studies, we explored expected changes in greater detail for six specific representative locations, covering the range from tropical to boreal forests. For most locations investigated, we calculated reductions in daily transpiration rates over the twenty-first century that became stronger under higher atmospheric CO2 concentrations. It showed that the effect of CO2-induced reduction of stomatal conductance would have a stronger transpiration-depressing effect than the stimulatory effect of future warming. For currently cold regions, global warming would, however, lengthen the growing seasons so that annual sums of transpiration could increase in those regions despite reductions in daily transpiration rates over the summer months.

Warming and snow loss increase reliance on old groundwater in a Colorado River headwater

Nature Portfolio (Springer Nature) | April 8th, 2026

Atmospheric warming is reducing snowpack, with uncertain effects on mountainous streamflow, a crucial water resource. Despite limited historical observations of groundwat

Atmospheric warming is reducing snowpack, with uncertain effects on mountainous streamflow, a crucial water resource. Despite limited historical observations of groundwater–streamflow interactions above 2,500 m, new measurements in the Upper Colorado River headwaters indicate declining groundwater storage that is dated decades to millennia old. Here we use integrated hydrologic modelling spanning water years 2015–2021 to determine whether the loss of old-age groundwater buffers streamflow during low-snow years and whether that loss is exacerbated with warming. Results show that old-groundwater contributions to streams remain relatively steady through time, unlike the more variable contributions from young groundwater. Numerical experiments of increased surface air temperatures (+2.5 °C and +4 °C) increase rain–snow fractions and evapotranspiration and decrease runoff ratio by 2–3% per degree Celsius increase. As streamflow declines with warming, the age of groundwater supporting it gets older, in part owing to intermediate-aged (1–3 year) groundwater declining twice as fast. Simulations show that water table depths at higher elevations (>3,700 m) decline disproportionately and fail to recover even during wet years. These findings suggest altered groundwater–streamflow interactions with warming and snow loss, with implications for water resources.

Warming weakens the night-time barrier to global fire

Nature Portfolio (Springer Nature) | February 16th, 2022

Night-time provides a critical window for slowing or extinguishing fires owing to the lower temperature and the lower vapour pressure deficit (VPD). However, fire danger

Night-time provides a critical window for slowing or extinguishing fires owing to the lower temperature and the lower vapour pressure deficit (VPD). However, fire danger is most often assessed based on daytime conditions1,2, capturing what promotes fire spread rather than what impedes fire. Although it is well appreciated that changing daytime weather conditions are exacerbating fire, potential changes in night-time conditions—and their associated role as fire reducers—are less understood. Here we show that night-time fire intensity has increased, which is linked to hotter and drier nights. Our findings are based on global satellite observations of daytime and night-time fire detections and corresponding hourly climate data, from which we determine landcover-specific thresholds of VPD (VPDt), below which fire detections are very rare (less than 95 per cent modelled chance). Globally, daily minimum VPD increased by 25 per cent from 1979 to 2020. Across burnable lands, the annual number of flammable night-time hours—when VPD exceeds VPDt—increased by 110 hours, allowing five additional nights when flammability never ceases. Across nearly one-fifth of burnable lands, flammable nights increased by at least one week across this period. Globally, night fires have become 7.2 per cent more intense from 2003 to 2020, measured via a satellite record. These results reinforce the lack of night-time relief that wildfire suppression teams have experienced in recent years. We expect that continued night-time warming owing to anthropogenic climate change will promote more intense, longer-lasting and larger fires.

Waste Not, Want Not: The Potential for Urban Water Conservation in California

Pacific Institute | November 1st, 2003

The largest, least expensive, and most environmentally sound source of water to meet California’s future needs is the water currently being wasted in every sector of

The largest, least expensive, and most environmentally sound source of water to meet California’s future needs is the water currently being wasted in every sector of our economy. That’s the core message of a major new report on urban water use in California released by the Pacific Institute of Oakland, California. “Waste Not, Want Not: The Potential for Urban Water Conservation in California,”in preparation for three years, is the first report to look comprehensively at residential, commercial, institutional, and industrial water use in the state — and then evaluate the potential for reducing this use through conservation and efficiency. Despite the progress California has already made in improving water efficiency, “Waste Not, Want Not” estimates that up to one-third of California’s current urban water use — more than 2.3 million acre-feet — can be saved using existing technology. And at least 85% of this savings (over 2 million acre-feet) can be saved at costs below what it will cost to tap into new sources of supply and without the social, environmental, and economic impacts that any major water project will bring.

Wasted Water: Reasonable Use Law in 21st Century California

Publisher not available | January 24th, 2015

The 2015 California Water Law Symposium focused on the reasonable use of water in modern day California. Panel topics: The Long View on Reasonable Use Law in Cali

The 2015 California Water Law Symposium focused on the reasonable use of water in modern day California. Panel topics: The Long View on Reasonable Use Law in California A Tale of Two Counties: Efficiency in a Modern Climate "Just" Pricing: Water Affordability and California's Human Right to Water Sustainable Groundwater Management The Role of Reasonable Use Law in the Russian River Frost Protection Litigation Advancements and Challenges in Agricultural Water Use Efficiency Since 2009

Wastewater Infrastructure: Overview, Funding, and Legislative Developments

Congressional Research Service (CRS) | September 22nd, 2017

The collection and treatment of wastewater remains among the most important public health interventions in human history and has contributed to a significant decrease in

The collection and treatment of wastewater remains among the most important public health interventions in human history and has contributed to a significant decrease in waterborne diseases during the past century. Nevertheless, waste discharges from municipal sewage treatment plants into rivers and streams, lakes, and estuaries and coastal waters remain a significant source of water quality problems throughout the country. The Clean Water Act (CWA) establishes performance levels to be attained by municipal sewage treatment plants in order to prevent the discharge of harmful wastes into surface waters. The act also provides financial assistance so that communities can construct treatment facilities and related equipment to comply with the law. Although approximately $95 billion in CWA assistance has been provided since 1972, funding needs for wastewater infrastructure remain high. According to the most recent estimate by the Environmental Protection Agency and the states, the nation’s wastewater treatment facilities will need $271 billion over the next 20 years to meet the CWA’s water quality objectives. Meeting the nation’s wastewater infrastructure needs efficiently and effectively is likely to remain an issue of considerable interest to policymakers. The CWA authorizes the principal federal program to support wastewater treatment plant construction and related eligible activities. Congress established the CWA Title II construction grants program in 1972, significantly enhancing what had previously been a modest grant program. Federal funds were provided through annual appropriations under a state-by-state allocation formula contained in the act. States used their allotments to make grants to cities to build or upgrade categories of wastewater treatment projects including treatment plants, related interceptor sewers, correction of infiltration/inflow of sewer lines, and sewer rehabilitation. In 1987, Congress amended the CWA and created the State Water Pollution Control Revolving Fund (SRF) program. This program represented a major shift in how the nation finances wastewater treatment needs. In contrast to the Title II construction grants program, which provided grants directly to localities, SRFs are loan programs. States use their SRFs to provide several types of loan assistance to communities, including project construction loans made at or below market interest rates, refinancing of local debt obligations, providing loan guarantees, and purchasing insurance. In 2014, Congress revised the SRF program by providing additional loan subsidies (including forgiveness of principal and negative interest loans) in certain instances. The law identifies a number of types of projects as eligible for SRF assistance, including wastewater treatment plant construction, stormwater treatment and management, energy-efficiency improvements at treatment works, reuse and recycling of wastewater or stormwater, and security improvements at treatment works. In both FY2016 and FY2017, Congress provided $1.394 billion for the clean water SRF program. President Trump’s FY2018 budget proposal requests the same amount as provided for the previous two fiscal years. Although appropriation levels have remained consistent in recent years (in nominal dollars), policymakers have continued to propose changes to the funding program. Issues debated in connection with these proposals include extending SRF assistance to help states and cities meet the estimated funding needs, modifying the program to assist small and economically disadvantaged communities, and enhancing the SRF program to address a number of water quality priorities beyond traditional treatment plant construction—particularly the management of wet weather pollutant runoff from numerous sources, which is the leading cause of stream and lake impairment nationally.

Wastewater Reuse for Agriculture: Development of a Regional Water Reuse Decision-Support Model (RWRM) for Cost-Effective Irrigation Sources

American Chemical Society (ACS) | August 8th, 2016

Water scarcity has become a critical problem in many semiarid and arid regions. The single largest water use in such regions is for crop irrigation, which typically relie

Water scarcity has become a critical problem in many semiarid and arid regions. The single largest water use in such regions is for crop irrigation, which typically relies on groundwater and surface water sources. With increasing stress on these traditional water sources, it is important to consider alternative irrigation sources for areas with limited freshwater resources. One potential irrigation water resource is treated wastewater for agricultural fields located near urban centers. In addition, treated wastewater can contribute an appreciable amount of necessary nutrients for plants. The suitability of reclaimed water for specific applications depends on water quality and usage requirements. The main factors that determine the suitability of recycled water for agricultural irrigation are salinity, heavy metals, and pathogens, which cause adverse effects on human, plants, and soils. In this paper, we develop a regional water reuse decision-support model (RWRM) using the general algebraic modeling system to analyze the cost-effectiveness of alternative treatment trains to generate irrigation water from reclaimed wastewater, with the irrigation water designed to meet crop requirements as well as California’s wastewater reuse regulations (Title 22). Using a cost-minimization framework, least-cost solutions consisting of treatment processes and their intensities (blending ratios) are identified to produce alternative irrigation sources for citrus and turfgrass. Our analysis illustrates the benefits of employing an optimization framework and flexible treatment design to identify cost-effective blending opportunities that may produce high-quality irrigation water for a wide range of end uses.

Wastewater surveillance for public health

American Association for the Advancement of Science (AAAS) | January 5th, 2023

Water & Power Rates Request 2016-2020 Frequently Asked Questions

Los Angeles Department of Water & Power (LADWP) | January 21st, 2016

Water Accounting in Western US, Australia, and Spain: Comparative Analysis

American Society of Civil Engineers (ASCE) | January 10th, 2020