Quantifying the influence of global warming on unprecedented extreme climate events

National Academy of Sciences (NAS) | April 24th, 2017

Efforts to understand the influence of historical global warming on individual extreme climate events have increased over the past decade. However, despite substa

Efforts to understand the influence of historical global warming on individual extreme climate events have increased over the past decade. However, despite substantial progress, events that are unprecedented in the local observational record remain a persistent challenge. Leveraging observations and a large climate model ensemble, we quantify uncertainty in the influence of global warming on the severity and probability of the historically hottest month, hottest day, driest year, and wettest 5-d period for different areas of the globe. We find that historical warming has increased the severity and probability of the hottest month and hottest day of the year at >80% of the available observational area. Our framework also suggests that the historical climate forcing has increased the probability of the driest year and wettest 5-d period at 57% and 41% of the observed area, respectively, although we note important caveats. For the most protracted hot and dry events, the strongest and most widespread contributions of anthropogenic climate forcing occur in the tropics, including increases in probability of at least a factor of 4 for the hottest month and at least a factor of 2 for the driest year. We also demonstrate the ability of our framework to systematically evaluate the role of dynamic and thermodynamic factors such as atmospheric circulation patterns and atmospheric water vapor, and find extremely high statistical confidence that anthropogenic forcing increased the probability of record-low Arctic sea ice extent.

Quantifying the Multiplier Effect of Southern California’s Turf Removal Rebate Program with Time-Series Aerial Imagery

American Water Resources Association (AWRA) | December 30th, 2020

From 2014 to 2016, water agencies in Southern California provided more than $350 million in rebates to owners who converted their turf to drought-tolerant landscaping. In

From 2014 to 2016, water agencies in Southern California provided more than $350 million in rebates to owners who converted their turf to drought-tolerant landscaping. In order to provide a fuller understanding of the water savings of this program, this study establishes that there was a behavioral contagion, or a multiplier effect, from rebate participants in the program. An imagery-based, time-series analysis of 20 Southern California neighborhoods from 2012 to 2018 was performed to detect what parcels converted their lawns without a rebate and how they were spatially correlated with rebate participants. This correlation was then used on almost 55,000 rebate participants to estimate the multiplier benefits for the entire program at 132%. For every 100 rebate participants, the multiplier effect helped contribute to an additional 132 parcels to convert to drought-tolerant landscaping. This methodology was compared with a previous study in the Irvine Ranch Water District providing similar results. This study provides the Metropolitan Water District of Southern California a better understanding of the water savings per rebate dollar of the Turf Removal Rebate Program as well as providing a robust approach for cities or water agencies to estimate the multiplier effect of their turf rebate programs.

Quantifying the Relationship Between Atmospheric River Origin Conditions and Landfall Temperature

American Geophysical Union (AGU) | October 11th, 2022

The temperature of landfalling atmospheric rivers (ARs) has direct implications for regional water resources. Compared to cool ARs, warm ARs can result in more surface ru

The temperature of landfalling atmospheric rivers (ARs) has direct implications for regional water resources. Compared to cool ARs, warm ARs can result in more surface runoff and flooding, less water availability via low snow accumulations and enhanced snowmelt, and greater challenges for storm forecasting and reservoir operations. Based on case studies, ARs with subtropical origin locations and warm origin conditions are assumed to be associated with warmer landfall temperatures—though, to date, this has not yet been demonstrated systematically. We analyze North Pacific ARs that made landfall along the West Coast of North America from 1980 to 2017. We find that ARs originating over the subtropical Pacific Ocean near Hawaii (“Pineapple Express”-type ARs) are indeed 1.5°C warmer and 2 kg/m2 moister in winter than ARs originating elsewhere. We extend this analysis for the full study population of ARs by quantifying AR origin conditions, including the spatial distribution of origin temperature, moisture content, and integrated vapor transport (IVT). We use fixed effects multivariate regression to quantify the relative influence of the origin conditions on landfall temperature. Our regression models show that AR origins with lower latitudes, longer AR lifetimes, and stronger IVT are associated with warmer landfall temperatures and that ARs that start warm generally stay warm. We also find that the phase of the El Niño/Southern Oscillation does not exhibit a consistent relationship with AR landfall temperature. Overall, our results partially affirm—yet also complicate—common assumptions about the role of different origin conditions in landfalling AR temperature.

Quantifying the role of atmospheric rivers in the interior western United States

Royal Meteorological Society (RMS) | July 13th, 2012

Atmospheric rivers (ARs) have increasingly been recognized for their contribution to high-impact weather and climate variability. A recent investigation based on observat

Atmospheric rivers (ARs) have increasingly been recognized for their contribution to high-impact weather and climate variability. A recent investigation based on observations located primarily in lowland valleys and basins of the western United States suggests that 10 – 50% of the total cool season (November to April) precipitation between water years 1998 and 2008 occurred on the day of and day following AR landfall (hereafter the AR fraction), as identified using  Special Sensor Microwave Imager data. However, these results are based only on ARs crossing the North American west coast between 32.5◦N and 52.5◦N, which excludes those crossing the west coast of the Baja Peninsula. Here, we identify ARs in the ERA-Interim reanalysis and examine the AR fraction at high-elevation observational sites and in the NOAA/CPC Unified Daily Precipitation Analysis. At high-elevation snowpack telemetry sites, we find good agreement with the AR fraction obtained previously for valley and basin locations. We also show that including ARs crossing the west coast of the Baja Peninsula (as far south as 24◦N) substantially increases the AR fraction over the southwestern United States

Racanelli Decision: Detailed summary of the decision

Department of Justice (DOJ) | November 16th, 2007

At their meeting on October 25, 2007, the Delta Vision Blue Ribbon Task Force members asked for a summary of United States v. State Water Resources Control Board (1986) 1

At their meeting on October 25, 2007, the Delta Vision Blue Ribbon Task Force members asked for a summary of United States v. State Water Resources Control Board (1986) 182 Cal.App.3d 82, commonly referred to as the “Racanelli Decision,” after the appellate judge who wrote the opinion. We repeat the Court’s own very short summary of the case, followed by a more detailed summary of the decision.

Rain Making

Scientific American | August 11th, 1894

I SHALL ask your attention this evening to the scientific principles which are involved in the condensation of atmospheric vapor, and to some of the attempts which have

I SHALL ask your attention this evening to the scientific principles which are involved in the condensation of atmospheric vapor, and to some of the attempts which have been made to produce this condensation by artificial means. Since the change from atmospheric vapor to water involves a change of the physical state of the same substance from a gas to a liquid.

Rainfall intensification amplifies exposure of American Southwest to conditions that trigger postfire debris flows

Nature Portfolio (Springer Nature) | June 7th, 2024

Rapid decline of California’s native inland fishes: a status assessment

University of California, Davis (UC Davis) | November 1st, 2010

Degradation of freshwater ecosystems is a global crisis best understood through intensive study of well-studied regional faunas. A quantitative protocol was used

Degradation of freshwater ecosystems is a global crisis best understood through intensive study of well-studied regional faunas. A quantitative protocol was used to determine conservation status of all 129 freshwater fishes native to California. Seven (5%) are extinct; 34 (26%) qualified for listing as endangered or threatened species; 32 (25%) were rated as imperiled, qualifying as California Species of Special Concern, with potential for listing; 34 (26%) rated being on a watch list and 22 (17%) were found to be relatively secure. Of 31 species officially listed under federal and state endangered species acts, 17 (55%) clearly qualified for listing under our criteria and 12 (39%) were rated as species of special concern. Conversely, of 34 extant species with the lowest ratings under our criteria, only 17 (50%) were officially listed. Climate change, area occupied and anthropogenic threats had the largest negative impact on status. Of the 15 categories of anthropogenic threats analyzed, those most likely to diminish status were alien species, agriculture and dams. Overall, 83% of California’s freshwater fishes are extinct, endangered, or in decline, a 16% increase since 1995 and a 21% increase since 1989. The decline seen in California’s inland fishes is probably typical of declines in areas that are less well documented, indicating a strong need for better methods of conservation of freshwater ecosystems.

Rapid emergence of climate change in environmental drivers of marine ecosystems

Nature Portfolio (Springer Nature) | March 7th, 2017

Climate change is expected to modify ecological responses in the ocean, with the potential for important effects on the ecosystem services provided to humankind

Climate change is expected to modify ecological responses in the ocean, with the potential for important effects on the ecosystem services provided to humankind. Here we address the question of how rapidly multiple drivers of marine ecosystem change develop in the future ocean. By analysing an ensemble of models we find that, within the next 15 years, the climate change-driven trends in multiple ecosystem drivers emerge from the background of natural variability in 55% of the ocean and propagate rapidly to encompass 86% of the ocean by 2050 under a ‘business-as-usual’ scenario. However, we also demonstrate that the exposure of marine ecosystems to climate change-induced stress can be drastically reduced via climate mitigation measures; with mitigation, the proportion of ocean susceptible to multiple drivers within the next 15 years is reduced to 34%. Mitigation slows the pace at which multiple drivers emerge, allowing an additional 20 years for adaptation in marine ecological and socio-economic systems alike.

Rapid groundwater decline and some cases of recovery in aquifers globally

Nature Portfolio (Springer Nature) | January 24th, 2024