Mechanisms of a Meteorological Drought Onset: Summer 2020 to Spring 2021 in Southwestern North America

American Meteorological Society (AMS) | November 1st, 2022

By summer 2021 moderate to exceptional drought impacted 28% of North America, focused west of the Mississippi, with serious impacts on fire, water resources, and agricult

By summer 2021 moderate to exceptional drought impacted 28% of North America, focused west of the Mississippi, with serious impacts on fire, water resources, and agriculture. Here, using reanalyses and SST-forced climate models, we examine the onset and development of this southwestern drought from its inception in summer 2020 through winter and spring 2020/21. The drought severity in summer 2021 resulted from four consecutive prior seasons in which precipitation in the southwest United States was the lowest on record or, at least, extremely dry. The dry conditions in summer 2020 arose from internal atmospheric variability but are beyond the range of what the studied atmosphere models simulate for that season. From winter 2020 through spring 2021 the worsening drought conditions were guided by the development of a La Niña in the tropical Pacific Ocean. Decadal variability in the Pacific Ocean aided drought in the southern part of the region by driving the cool season to be drier during the last two decades. There is also evidence that the southern part of the region in spring is drying due to human-driven climate change. In sum the drought onset was driven by a combination of internal atmospheric variability and interannual climate variability and aided by natural decadal variability and human-driven climate change.

Mediterranean California’s water use future under multiple scenarios of developed and agricultural land use change

PLOS | October 31st, 2017

With growing demand and highly variable inter-annual water supplies, California’s water use future is fraught with uncertainty. Climate change projections, anti

With growing demand and highly variable inter-annual water supplies, California’s water use future is fraught with uncertainty. Climate change projections, anticipated population growth, and continued agricultural intensification, will likely stress existing water supplies in coming decades. Using a state-and-transition simulation modeling approach, we examine a broad suite of spatially explicit future land use scenarios and their associated county-level water use demand out to 2062. We examined a range of potential water demand futures sampled from a 20-year record of historical (1992–2012) data to develop a suite of potential future land change scenarios, including low/high change scenarios for urbanization and agriculture as well as “lowest of the low” and “highest of the high” anthropogenic use. Future water demand decreased 8.3 billion cubic meters (Bm3) in the lowest of the low scenario and decreased 0.8 Bm3 in the low agriculture scenario. The greatest increased water demand was projected for the highest of the high land use scenario (+9.4 Bm3), high agricultural expansion (+4.6 Bm3), and high urbanization (+2.1 Bm3) scenarios. Overall, these scenarios show agricultural land use decisions will likely drive future demand more than increasing municipal and industrial uses, yet improved efficiencies across all sectors could lead to potential water use savings. Results provide water managers with information on diverging land use and water use futures, based on historical, observed land change trends and water use histories.

Megadroughts in the Common Era and the Anthropocene

Nature Portfolio (Springer Nature) | October 4th, 2022

Exceptional drought events, known as megadroughts, have occurred on every continent outside Antarctica over the past ~2,000 years, causing major ecological and societal

Exceptional drought events, known as megadroughts, have occurred on every continent outside Antarctica over the past ~2,000 years, causing major ecological and societal disturbances. In this Review, we discuss shared causes and features of Common Era (Year 1–present) and future megadroughts. Decadal variations in sea surface temperatures are the primary driver of megadroughts, with secondary contributions from radiative forcing and land–atmosphere interactions. Anthropogenic climate change has intensified ongoing megadroughts in south-western North America and across Chile and Argentina. Future megadroughts will be substantially warmer than past events, with this warming driving projected increases in megadrought risk and severity across many regions, including western North America, Central America, Europe and the Mediterranean, extratropical South America, and Australia. However, several knowledge gaps currently undermine confidence in understanding past and future megadroughts. These gaps include a paucity of high-resolution palaeoclimate information over Africa, tropical South America and other regions; incomplete representations of internal variability and land surface processes in climate models; and the undetermined capacity of water-resource management systems to mitigate megadrought impacts. Addressing these deficiencies will be crucial for increasing confidence in projections of future megadrought risk and for resiliency planning.

Megapluvials in Southwestern North America

American Geophysical Union (AGU) | March 25th, 2025

Droughts over the last century in Southwestern North America (SWNA) have had severe consequences for people and ecosystems across the region, most recently during the ear

Droughts over the last century in Southwestern North America (SWNA) have had severe consequences for people and ecosystems across the region, most recently during the early 21st-century megadrought (2000–2022). The 20thcentury, however, was bracketed by two extended pluvials that also had significant impacts in the region. We use a 1,224 years (800–2023 CE) record of observed and reconstructed soil moisture, in concert with a paleoclimate reanalysis product, to place the 20th-century pluvials in a longer-term context and investigate the occurrence and dynamics of similar events in the Common Era.

Memo: Effect of SWANCC vs. United States on the 401 certification program

California State Water Resources Control Board (SWRCB) | January 25th, 2001

This memorandum has been prepared to explain the effect of the recent US Supreme Court decision of Solid Waste Association of Northern Cook Counties v. United States Corp

This memorandum has been prepared to explain the effect of the recent US Supreme Court decision of Solid Waste Association of Northern Cook Counties v. United States Corps of Engineers (hereinafter “SWANCC”), which was issued on January 9th. The memo is intended to address the impact of the decision on the 401 program (33 U.S.C. § 1341), and to indicate alternative regulatory avenues available to the Regional Boards for waters that are no longer covered by section 404/401 jurisdiction.

Memo: Issues Related to Overlap between Pre-1914 and Riparian Water Right Claims in the Delta

California State Water Resources Control Board (SWRCB) | December 15th, 2017

To: Michael Patrick George, Delta Watermaster From: Micah Green, Water Rights Analyst Re: Issues Related to Overlap between Pre-1914 and Riparian Water Right Claims in

To: Michael Patrick George, Delta Watermaster From: Micah Green, Water Rights Analyst Re: Issues Related to Overlap between Pre-1914 and Riparian Water Right Claims in the Delta Date: December 15, 2017 Pursuant to your request, I have researched an issue raised in the course of my review of responses to the Division of Water Rights’ 2015 Information Order submitted by water right claimants within the Legal Delta. I. Question Presented Under California water law and within the Legal Delta, are there any circumstances under which riparian and appropriative rights can “overlap” becoming indistinguishable or inseparable such that either or both may be lawfully exercised at the election of the holder? II. Short Answer It is possible to perfect both riparian and appropriative water rights for beneficial use on the same parcel. However, riparian and appropriative rights are distinct property interests that must be separately established. There is no California precedent recognizing “overlapping” or “intertwined” water rights, and water laws against hoarding and non-use operate to preclude the duplicative exercise of water rights.

Memorandum of Understanding by and among Colorado River Basin Municipal and Public Water Providers

Southern Nevada Water Authority (SNWA) | November 15th, 2022

Memorandum Report on the Floods of January and February 1969 in the Southern District of the Department of Water Resources

California Department of Water Resources (DWR) | February 27th, 1970

Memorialization and Memory of Southern California's St. Francis Dam Disaster of 1928

California State University, Northridge (CSUN) | August 1st, 2014

The commemoration of disasters is a product of social, cultural, economic, and  political forces in human society. Southern California's largely unheard-of St. Francis D

The commemoration of disasters is a product of social, cultural, economic, and  political forces in human society. Southern California's largely unheard-of St. Francis Dam Disaster of 1928 provides an excellent opportunity to study this complex process of commemoration, engaging memory within difference frames of reference. In particular, evaluating how and why this man-made dam disaster has been forgotten on a state and national level, but tenuously remembered within the flood-zone, allows for consideration of the diversity of commemorative processes in the construction of memory and heritage related to major catastrophes.

Merced Groundwater Subbasin Groundwater Sustainability Plan

Merced Subbasin Groundwater Sustainability Agency (MSGSA) | November 12th, 2019