Relative impacts of mitigation, temperature, and precipitation on 21st-century megadrought risk in the American Southwest

American Association for the Advancement of Science (AAAS) | October 5th, 2016

Megadroughts are comparable in severity to the worst droughts of the 20th century but are of much longer duration. A megadrought in the American Southwest would

Megadroughts are comparable in severity to the worst droughts of the 20th century but are of much longer duration. A megadrought in the American Southwest would impose unprecedented stress on the limited water resources of the area, making it critical to evaluate future risks not only under different climate change mitigation scenarios but also for different aspects of regional hydroclimate. We find that changes in the mean hydroclimate state, rather than its variability, determine megadrought risk in the American Southwest. Estimates of megadrought probabilities based on precipitation alone tend to underestimate risk. Furthermore, business-as-usual emissions of greenhouse gases will drive regional warming and drying, regardless of large precipitation uncertainties. We find that regional temperature increases alone push megadrought risk above 70, 90, or 99% by the end of the century, even if precipitation increases moderately, does not change, or decreases, respectively. Although each possibility is supported by some climate model simulations, the latter is the most common outcome for the American Southwest in Coupled Model Intercomparison 5 generation models. An aggressive reduction in global greenhouse gas emissions cuts megadrought risks nearly in half.

Remote linkages to anomalous winter atmospheric ridging over the Northeastern Pacific

American Geophysical Union (AGU) | October 24th, 2017

Severe drought in California between 2013 and 2016 has previously been linked to the persistence of atmospheric high atmospheric pressure over the Pacific Ocean (nickname

Severe drought in California between 2013 and 2016 has previously been linked to the persistence of atmospheric high atmospheric pressure over the Pacific Ocean (nicknamed the “Ridiculously Resilient Ridge”), which prevented winter storms from reaching the coast over several consecutive years. There has been much discussion regarding why this high‐pressure system has been so persistent—and some scientists have previously suggested that unusual ocean temperature patterns in the Pacific, reductions in Arctic sea ice, or random weather variations may have played a role. In this study, we investigate relationships between atmospheric high pressure over the North Pacific and possible links to ocean conditions using both real‐world observations and climate model simulations. Our results suggest that persistent atmospheric high pressure similar to that which occurred during California's 2013–2016 drought can be partially linked to unusual Pacific Ocean temperatures and that knowledge of such ocean conditions may offer foresight regarding the potential for future droughts in this region.

Report on the Delta Drought Response Pilot Program for Water Year 2023

Sacramento-San Joaquin Delta Conservancy | July 24th, 2024

This report describes the 2023 Delta Drought Response Pilot Program (DDRPP/Program), provides an analysis of the Program’s effectiveness, and describes the Program outc

This report describes the 2023 Delta Drought Response Pilot Program (DDRPP/Program), provides an analysis of the Program’s effectiveness, and describes the Program outcomes, including findings and recommendations for application in future agricultural water conservation programs. The DDRPP launched in January 2022 as a response to the continuing risk of drought in the Sacramento-San Joaquin Delta Watershed. This report focuses on the results of the 2023 Program, with a brief analysis comparing both years of the Program. For detailed information on the 2022 Program and 2022 analysis, see the 2022 DDRPP Final Report (Sacramento-San Joaquin Delta Conservancy, 2023).

Ridging associated with drought in western and southwestern United States: characteristics, trends and predictability

American Meteorological Society (AMS) | April 1st, 2020

Persistent winter ridging events are a consistent feature of meteorological drought across the western and southwestern United States. In this study, a ridge detection al

Persistent winter ridging events are a consistent feature of meteorological drought across the western and southwestern United States. In this study, a ridge detection algorithm is developed and applied on daily geopotential height anomalies to track and quantify the diversity of individual ridge characteristics (e.g., position, frequency, magnitude, extent, and persistence). Three dominant ridge types are shown to play important, but differing, roles for influencing the location of landfalling atmospheric rivers (ARs), precipitation, and subsequently meteorological drought. For California, a combination of these ridge types is important for influencing precipitation deficits on daily through seasonal time scales, indicating the various pathways by which ridging can induce drought. Furthermore, both the frequency of ridge types and reduced AR activity are necessary features for explaining drought variability on seasonal time scales across the western and southwestern regions. The three ridge types are found to be associated in different ways with various remote drivers and modes of variability, highlighting possible sources of subseasonal-to-seasonal (S2S) predictability. A comparison between ridge types shows that anomalously large and persistent ridging events relate to different Rossby wave trains across the Pacific with different preferential upstream locations of tropical heating. For the “South-ridge” type, centered over the Southwest, a positive trend is found in both the frequency and persistence of these events across recent decades, likely contributing to observed regional drying. These results illustrate the utility of feature tracking for characterizing a wider range of ridging features that collectively influence precipitation deficits and drought.

Risk-Informed Future Climate Scenario Development for the State Water Project Delivery Capability Report

California Department of Water Resources (DWR) | August 24th, 2023

This report introduces and documents an extensive effort undertaken by the California Department of Water Resources (DWR) to develop risk-informed future climate scenario

This report introduces and documents an extensive effort undertaken by the California Department of Water Resources (DWR) to develop risk-informed future climate scenarios for the State Water Project (SWP) Delivery Capability Report (DCR), a report issued by the SWP every two years. These reports present DWR’s analysis of the SWP system and planning information for users of SWP water. The analysis provides information about how climate change, regulatory, and operational considerations affect SWP delivery capability. Specifically, the report must provide “…under a range of hydrologic conditions, the then existing overall delivery capability of the project facilities and the allocation of that capacity to each contractor. The range of hydrologic conditions shall include the historic extended dry cycle and long-term average.” (Settlement Agreement 2003).

Running Dry: Weathering the Great California Drought

Harvard University | December 1st, 2016

Essays include: "Physical Mechanisms of the California Drought" - Richard Seager "Droughts and the Global Economy: Lessons from California" - Jay R. Lund

Essays include: "Physical Mechanisms of the California Drought" - Richard Seager "Droughts and the Global Economy: Lessons from California" - Jay R. Lund "Addressing Variability: Adaptation and Innovation in California’s Water Systems" - Laila Kasuri "The California Case: Managing Groundwater in Irrigated Agriculture" - Josué Medellín-Azuara "The Hidden Health Consequences of Drought" - Rory Stewart & Erika Eitland "California’s Unconventional Energy-Water Nexus" - Jonathan Buonocore, Don Kriens, Susan Cahalan, Drew Michanowicz, Alexandra Gast, Kate Konschnik "The 2 R’s: What Brazil Can Teach Us About California’s Drought" -  Luis Augusto Bertoni Strengari "Carlsbad Desalination: A Leap in Water Prices, for the Better?" - Aldís Elfarsdóttir

Sacramento and San Joaquin river basins: Procedures for hydrologic analysis

U.S. Army Corps of Engineers (USACE) | September 9th, 2008

The primary purpose of this document is to describe the methods and procedures we will use to complete the hydrologic analysis of the Sacramento and San Joaquin river b

The primary purpose of this document is to describe the methods and procedures we will use to complete the hydrologic analysis of the Sacramento and San Joaquin river basins. Specifically, we describe the required inputs, models, analysis, and anticipated results. This description will give the HAC an opportunity to review, in advance, the procedures for the hydrologic analysis. The secondary purpose of this paper is to initiate development of a project management plan (PMP) by outlining specific procedural tasks to be completed in the hydrologic analysis.

Science and Decision Making: Water Management and Tree‐Ring Data in the Western United States

American Water Resources Association (AWRA) | October 5th, 2009

Growing populations, limited resources, and sustained drought are placing increased pressure on already over‐allocated water supplies in the western United States, prom

Growing populations, limited resources, and sustained drought are placing increased pressure on already over‐allocated water supplies in the western United States, prompting some water managers to seek out and utilize new forms of climate data in their planning efforts. One source of information that is now being considered by water resource management is extended hydrologic records from tree‐ring data. Scientists with the Western Water Assessment (WWA) have been providing reconstructions of streamflow (i.e., paleoclimate data) to water managers in Colorado and other western states (Arizona, New Mexico, and Wyoming), and presenting technical workshops explaining the applications of tree‐ring data for water management for the past eight years. Little is known, however, about what has resulted from these engagements between scientists and water managers. Using in‐depth interviews and a survey questionnaire, we attempt to address this lack of information by examining the outcomes of the interactions between WWA scientists and western water managers to better understand how paleoclimate data has been translated to water resource management. This assessment includes an analysis of what prompts water managers to seek out tree‐ring data, how paleoclimate data are utilized by water managers in both quantitative and qualitative ways, and how tree‐ring data are interpreted in the context of organization mandates and histories. We situate this study within a framework that examines the coproduction of science and policy, where scientists and resource managers collectively define and examine research and planning needs, the activities of which are embedded within wider social and political contexts. These findings have broader applications for understanding science‐policy interactions related to climate and climate change in resource management, and point to the potential benefits of reflexive interactions of scientists and decision makers.

Science be Dammed: How Ignoring Inconvenient Science Drained the Colorado River

University of Arizona Press | November 26th, 2019

Science Be Dammed is an alarming reminder of the high stakes in the management—and perils in the mismanagement—of water in the western United States.  It seems decep

Science Be Dammed is an alarming reminder of the high stakes in the management—and perils in the mismanagement—of water in the western United States.  It seems deceptively simple: even when clear evidence was available that the Colorado River could not sustain ambitious dreaming and planning by decision-makers throughout the twentieth century, river planners and political operatives irresponsibly made the least sustainable and most dangerous long-term decisions. Arguing that the science of the early twentieth century can shed new light on the mistakes at the heart of the over-allocation of the Colorado River, authors Eric Kuhn and John Fleck delve into rarely reported early studies, showing that scientists warned as early as the 1920s that there was not enough water for the farms and cities boosters wanted to build. Contrary to a common myth that the authors of the Colorado River Compact did the best they could with limited information, Kuhn and Fleck show that development boosters selectively chose the information needed to support their dreams, ignoring inconvenient science that suggested a more cautious approach. Today water managers are struggling to come to terms with the mistakes of the past. Focused on both science and policy, Kuhn and Fleck unravel the tangled web that has constructed the current crisis. With key decisions being made now, including negotiations for rules governing how the Colorado River water will be used after 2026, Science Be Dammed offers a clear-eyed path forward by looking back. Understanding how mistakes were made is crucial to understanding our contemporary problems. Science Be Dammed offers important lessons in the age of climate change about the necessity of seeking out the best science to support the decisions we make.

Securing Color River Supplies - An Urban-Agriculture Partnership in the Palo Verde Valley

Metropolitan Water District of Southern California (MWD) | March 16th, 2022