The growing threat of multiyear droughts

American Association for the Advancement of Science (AAAS) | January 25th, 2025

Droughts have major societal and ecological impacts, including drinking water shortages, crop failures, tree mortality, wildfires, and reduced ecosystem productivity (1).

Droughts have major societal and ecological impacts, including drinking water shortages, crop failures, tree mortality, wildfires, and reduced ecosystem productivity (1). Shifts in the hydrological cycle and continued warming with climate change are leading to rapidly evolving droughts that are more intense and longer lasting (2). Extreme but short-term droughts (<1 year) can have a wide range of consequences, depending on the severity and timing of the drought as well as an ecosystem’s resistance (3, 4). However, as a drought extends to a multiyear event, these ecological effects can amplify because short-lived buffering from physiological adaptations or water storage may weaken, leading to longer-lasting results (4). On page 278 of this issue, Chen et al. (5) report that increasing precipitation anomalies and atmospheric moisture demands are leading to multiyear droughts with growing impacts on vegetation. This highlights the need to better understand the ecological responses to such drought events.

The Impact of a Severe Drought on Dust Lifting in California’s Owens Lake Area

Nature Portfolio (Springer Nature) | May 11th, 2017

Mineral dust aerosols are responsible for some of the largest sources of uncertainties in our current understanding of climate change. Here we show that a severe drought

Mineral dust aerosols are responsible for some of the largest sources of uncertainties in our current understanding of climate change. Here we show that a severe drought is having a significant impact in one of largest sources of mineral dust aerosols of the U.S., the Owens Lake area in California’s southwest. Measurements of aerosol concentration (PM2.5 particle matter) in the Owens Lake salty playa show that the annual mean concentration of PM2.5 aerosol has been increasing steadily since the beginning of the current drought, with periods of high aerosol concentration increasing from 4 months in 2013 to 9 months in 2015. Interestingly, the PM2.5 aerosol concentration usually increases abruptly from less than ~0.05 mg/m3 to ~0.25 mg/m3. This occurs when saltation events break salt crusts produced by the efflorescence of brine in the salty playa. The brine is produced by either rainfall or runoff water. Based on this observation, we hypothesize that there is an upper limit of ~0.25 mg/m3 in the annual mean PM2.5 aerosols concentration in the Owens Lake basin that might limit the impact of mineral dust aerosols on climate. Indeed, the upper annual limit of ~0.25 mg/m3 has been nearly reached during the current drought.

The implications of drought and water conservation on the reuse of municipal wastewater: Recognizing impacts and identifying mitigation possibilities

Water Research, Elsevier | November 1st, 2017

As water agencies continue to investigate opportunities to increase resilience and local water supply reliability in the face of drought and rising water scarcity, wa

As water agencies continue to investigate opportunities to increase resilience and local water supply reliability in the face of drought and rising water scarcity, water conservation strategies and the reuse of treated municipal wastewater are garnering significant attention and adoption. Yet a simple water balance thought experiment illustrates that drought, and the conservation strategies that are often enacted in response to it, both likely limit the role reuse may play in improving local water supply reliability. For instance, as a particular drought progresses and agencies enact water conservation measures to cope with drought, influent flows likely decrease while influent pollution concentrations increase, particularly salinity, which adversely affects wastewater treatment plant (WWTP) costs and effluent quality and flow. Consequently, downstream uses of this effluent, whether to maintain streamflow and quality, groundwater recharge, or irrigationmay be impacted. This is unfortunate since reuse is often heralded as a drought-proof mechanism to increase resilience. The objectives of this paper are two-fold. First, we illustrate—using a case study from Southern California during its most recent drought— how drought and water conservation strategies combine to reduce influent flow and quality and, subsequently, effluent flow and quality. Second, we use a recently developed regional water reuse decision support model (RWRM) to highlight cost-effective strategies that can be implemented to mitigate the impacts of drought on effluent water quality. While the solutions we identify cannot increase the flow of influent or effluent coming into or out of a treatment plant, they can improve the value of the remaining effluent in a cost-effective manner that takes into account the characteristics of its demand, whether it be for landscaping, golf courses, agricultural irrigation, or surface water augmentation.

The key role of dry days in changing regional climate and precipitation regimes

Nature Portfolio (Springer Nature) | March 13th, 2014

Future changes in the number of dry days per year can either reinforce or counteract projected increases in daily precipitation intensity as the climate warms. We

Future changes in the number of dry days per year can either reinforce or counteract projected increases in daily precipitation intensity as the climate warms. We analyze climate model projected changes in the number of dry days using 28 coupled global climate models from the Coupled Model Intercomparison Project, version 5 (CMIP5). We find that the Mediterranean Sea region, parts of Central and South America, and western Indonesia could experience up to 30 more dry days per year by the end of this century. We illustrate how changes in the number of dry days and the precipitation intensity on precipitating days combine to produce changes in annual precipitation, and show that over much of the subtropics the change in number of dry days dominates the annual changes in precipitation and accounts for a large part of the change in interannual precipitation variability.

The Lower Colorado Basin Fiscal Years 2019 & 2020

U.S. Bureau of Reclamation (USBR) | January 4th, 2021

The Northern California 2018 Extreme Fire Season

American Meteorological Society (AMS) | February 19th, 2020

The fire season of 2018 was the most extreme on record in Northern California in terms of the number of fatalities (95), over 22,000 structures destroyed, and over 600,00

The fire season of 2018 was the most extreme on record in Northern California in terms of the number of fatalities (95), over 22,000 structures destroyed, and over 600,000 ha burned. The most deadly and destructive fire in California history, the Camp Fire, occurred in Butte County in the Sierra Nevada foothills in early November, and caused 85 fatalities and destroyed nearly 19,000 structures. The largest fire complex in state history, the Mendocino Complex, which included the Ranch fire, the largest single fire in state history, burned nearly 186,000 ha. It occurred in July and August, killing one firefighter. In western Shasta County nearly 138,000 ha burned from July through September in the Carr, Hirz, and Delta Fires. These fires caused multiple closures of Interstate 5 and exhibited some of the most extreme fire behavior ever observed in California. The Carr Fire caused eight fatalities, including two firefighters and two workers supporting firefighting efforts, burned over 1,100 homes in west Redding, caused the evacuation of one-third of the city, and produced an extreme fire vortex with an Enhanced Fujita scale rating between 136 to 165 mph, making it arguably the strongest tornado type event in state history, and one of the strongest documented cases in the world (Lareau et al. 2018).

The reduced net carbon uptake over Northern Hemisphere land causes the close-to-normal CO2 growth rate in 2021 La Niña

American Association for the Advancement of Science (AAAS) | June 7th, 2024

The Role of Snowpack, Rainfall, and Reservoirs in Buffering California Against Drought Effects

U.S. Geological Survey (USGS) | August 1st, 2016

California’s vast reservoir system, fed by annual snow and rainfall, plays an important part in providing water to the State’s human and wildlife population. There ar

California’s vast reservoir system, fed by annual snow and rainfall, plays an important part in providing water to the State’s human and wildlife population. There are almost 1,300 reservoirs throughout the State, but only approximately 200 of them are considered storage reservoirs, and many of the larger ones are critical components of the Federal Central Valley Project and California State Water Project. Storage reservoirs, such as the ones shown in figure 1, capture winter precipitation for use in California’s dry summer months. In addition to engineered reservoir storage, California also depends on water “stored” in the statewide snowpack, which slowly melts during the course of the summer, to augment the State’s water supply.

The seven Colorado River Basin states letter to the U.S. Bureau of Reclamation, 5/22/23

U.S. Bureau of Reclamation (USBR) | May 22nd, 2023

The twenty-first century Colorado River hot drought and implications for the future

American Geophysical Union (AGU) | February 17th, 2017

Between 2000 and 2014, annual Colorado River flows averaged 19% below the 1906–1999 average, the worst 15-year drought on record. At least one-sixth to one-half (averag

Between 2000 and 2014, annual Colorado River flows averaged 19% below the 1906–1999 average, the worst 15-year drought on record. At least one-sixth to one-half (average at one-third) of this loss is due to unprecedented temperatures (0.9°C above the 1906–1999 average), confirming model-based analysis that continued warming will likely further reduce flows. Whereas it is virtually certain that warming will continue with additional emissions of greenhouse gases to the atmosphere, there has been no observed trend toward greater precipitation in the Colorado Basin, nor are climate models in agreement that there should be a trend. Moreover, there is a significant risk of decadal and multidecadal drought in the coming century, indicating that any increase in mean precipitation will likely be offset during periods of prolonged drought. Recently published estimates of Colorado River flow sensitivity to temperature combined with a large number of recent climate model-based temperature projections indicate that continued business-as-usual warming will drive temperature-induced declines in river flow, conservatively −20% by midcentury and −35% by end-century, with support for losses exceeding −30% at midcentury and −55% at end-century. Precipitation increases may moderate these declines somewhat, but to date no such increases are evident and there is no model agreement on future precipitation changes. These results, combined with the increasing likelihood of prolonged drought in the river basin, suggest that future climate change impacts on the Colorado River flows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur.