Flood Runoff in Relation to Water Vapor Transport by Atmospheric Rivers Over the Western United States, 1949–2015

American Geophysical Union (AGU) | November 29th, 2017

Atmospheric rivers (ARs) have a significant role in generating floods across the western United States. We analyze daily streamflow for water years 1949 to 2015 from 5,

Atmospheric rivers (ARs) have a significant role in generating floods across the western United States. We analyze daily streamflow for water years 1949 to 2015 from 5,477 gages in relation to watervapor transport by ARs using a 6 h chronology resolved to 2.5° latitude and longitude. The probability that an AR will generate 50 mm/d of runoff in a river on the Pacific Coast increases from 12% when daily mean water vapor transport, DVT, is greater than 300 kg m
1s
1to 54% when DVT>600 kg m
1s
1. Extreme runoff, represented by the 99th quantile of daily values, doubles from 80 mm/d at DVT = 300 kg m
1s
1to160 mm/d at DVT = 500 kg m
1s
1. Forecasts and predictions of water vapor transport by atmospheric rivers can support flood risk assessment and estimates of future flood frequencies and magnitude in the western United States.

Flood-Hazard Study -- 100 Year Flood Stage for Lucerne Lake, San Bernardino County, California

U.S. Geological Survey (USGS) | July 15th, 1977

Flood-Hazard Study -- 100-Year Flood Stage for Apple Valley Dry Lake, San Bernardino County, California

U.S. Geological Survey (USGS) | June 30th, 1975

A study of the flood hydrology of Apple Valley, Calif., was undertaken to develop the 100—year flood stage for Apple Valley dry lake. Synthetic hydrologic techniques we

A study of the flood hydrology of Apple Valley, Calif., was undertaken to develop the 100—year flood stage for Apple Valley dry lake. Synthetic hydrologic techniques were used because no adequate hydrologic or meteorologic data were available for the basin. The 100—year flood stage was estimated to be at an elevation of 2,909.0 feet (886.7 metres) above mean sea level.

From Climate Traces to Climate Insights: Future Scenarios Analysis for the California Central Valley

California Department of Water Resources (DWR) | October 2nd, 2023

California Water Code Section 10004.6 requires the California Department of Water Resources (DWR) to quantify current and future water conditions in the state. This infor

California Water Code Section 10004.6 requires the California Department of Water Resources (DWR) to quantify current and future water conditions in the state. This information is published in the California Water Plan (Water Plan), which is updated every five years. Water managers and planners constantly face the challenges of planning for an uncertain future where the only constant is change. To address the potential future changes and mitigate the probable risks, water managers must consider and quantify uncertainties and their impacts on water system vulnerability. Although it is not possible to know for certain how population growth, land use decisions, climate, and other factors change over time, water planners must consider these system stressors in long-term planning to evaluate future risks and uncertainty. The Water Plan evaluates many alternative future scenarios as an integral part of its analytical approach to quantify system vulnerability under a range of population and urban growth scenarios, land use, and climate uncertainties.

From Climate-Change Spaghetti to Climate-Change Distributions for 21st Century California

University of California, Davis (UC Davis) | March 1st, 2005

The uncertainties associated with climate-change projections for California are unlikely to disappear anytime soon, and yet important long-term decisions will be needed t

The uncertainties associated with climate-change projections for California are unlikely to disappear anytime soon, and yet important long-term decisions will be needed to accommodate those potential changes. Projection uncertainties have typically been addressedby analysis of a few scenarios, chosen based on availability or to capture the extreme cases among available projections. However, by focusing on more com-mon projections rather than the most extreme projections (using a new resampling method), new insights into current projections emerge: (1) uncertainties associated with future greenhouse-gas emissions are comparable with the differences among climate models, so that neither source of uncertainties should be neglected or underrepresented; (2) twenty-first century temperature projections spread more, overall, than do precipitation scenarios; (3) projections of extremely wet futures for California are true outliers among current projections; and (4) current projections that are warmest tend, overall, to yield a moderately drier California, while the cooler projections yield a some-what wetter future. The resampling approach appliedin this paper also provides a natural opportunity to objectively incorporate measures of model skill and the likelihoods of various emission scenarios into future assessments.

Future Atmospheric Rivers and Impacts on Precipitation: Overview of the ARTMIP Tier 2 High-Resolution Global Warming Experiment

American Geophysical Union (AGU) | March 14th, 2023

Atmospheric rivers (ARs) are long and narrow weather features often referred to as “rivers in the sky.” They often transport water from lower latitudes to higher lati

Atmospheric rivers (ARs) are long and narrow weather features often referred to as “rivers in the sky.” They often transport water from lower latitudes to higher latitudes typically across climate zones and produce precipitation necessary for local climates. Understanding ARs in a warming climate is challenging because of the variety of ways an AR can be defined on gridded data sets. Unlike weather features such as tropical cyclones where identification methodologies are similar, algorithms that determine the characteristics of ARs vary depending on the science question posed. Because there is no real consensus on AR identification methodology, we aim to quantify the algorithmic uncertainty in AR metrics and precipitation. We compare 16 different ways of defining an AR on gridded data sets and present the range of possibilities in which an AR could change under global warming. Generally, ARs are projected to increase but the amount of that increase is a function of the algorithm. Across all algorithms and focus regions, AR precipitation is projected to become more extreme.

Future Changes in Global Atmospheric Rivers Projected by CMIP6 Models

American Geophysical Union (AGU) | January 31st, 2024

Future dryness in the southwest US and the hydrology of the early 21st century drought

National Academy of Sciences (NAS) | December 14th, 2010

Recently the Southwest has experienced a spate of dryness, which presents a challenge to the sustainability of current water use by human and natural systems in

Recently the Southwest has experienced a spate of dryness, which presents a challenge to the sustainability of current water use by human and natural systems in the region. In the Colorado River Basin, the early 21st century drought has been the most extreme in over a century of Colorado River flows, and might occur in any given century with probability of only 60%. However, hydrological model runs from downscaled Intergovernmental Panel on Climate Change Fourth Assessment climate change simulations suggest that the region is likely to become drier and experience more severe droughts than this. In the latter half of the 21st century the models produced considerably greater drought activity, parti- cularly in the Colorado River Basin, as judged from soil moisture anomalies and other hydrological measures. As in the historical record, most of the simulated extreme droughts build up and per- sist over many years. Durations of depleted soil moisture over the historical record ranged from 4 to 10 years, but in the 21st century simulations, some of the dry events persisted for 12 years or more. Summers during the observed early 21st century drought were re- markably warm, a feature also evident in many simulated droughts of the 21st century. These severe future droughts are aggravated by enhanced, globally warmed temperatures that reduce spring snowpack and late spring and summer soil moisture. As the climate continues to warm and soil moisture deficits accumulate beyond historical levels, the model simulations suggest that sustaining water supplies in parts of the Southwest will be a challenge.

Future extreme precipitation amplified by intensified mesoscale moisture convergence

Nature Portfolio (Springer Nature) | November 18th, 2025

Extreme precipitation events are driven by complex multiscale atmospheric dynamic interactions, fuelled by available moisture. They are expected to intensify with

Extreme precipitation events are driven by complex multiscale atmospheric dynamic interactions, fuelled by available moisture. They are expected to intensify with climate change, posing increasing risks to human communities and ecosystems. However, current low-resolution climate models struggle to accurately represent key extreme precipitation-generating phenomena, limiting our ability to generate robust and reliable future projections. Here we present an ensemble of climate simulations with a 10-to-25-km resolution and an improved representation of mesoscale convective systems to assess future changes in daily extreme precipitation and its drivers. Our high-resolution simulations more realistically capture the observed spatial distribution and intensity of daily extreme precipitation over the historical period than the 100-km resolution counterparts. In a future scenario with high carbon dioxide emissions, daily extreme precipitation over land could increase by about 41% by 2100, mainly as a result of increased mesoscale moisture convergence. The impact of this dynamical contribution to extreme precipitation is underestimated by a factor of three in the low-resolution model. These results highlight the crucial role of high-resolution climate modelling in constraining future extremes and informing more effective climate risk assessments and adaptation strategies. Click here for a Science news article on the model and its evolution.  

Future land-use related water demand in California

Environmental Research Letters (IOP) | May 18th, 2019

Water shortages in California are a growing concern amidst ongoing drought, earlier spring snowmelt, projected future climate warming, and currently mandated water use r

Water shortages in California are a growing concern amidst ongoing drought, earlier spring snowmelt, projected future climate warming, and currently mandated water use restrictions. Increases in population and land use in coming decades will place additional pressure on already limited available water supplies. We used a state-and-transition simulation model to project future changes in developed (municipal and industrial) and agricultural land use to estimate associated water use demand from 2012 to 2062. Under current efficiency rates, total water use was projected to increase 1.8 billion cubic meters (+4.1%) driven primarily by urbanization and shifts to more water intensive crops. Only if currently mandated 25% reductions in municipal water use are continuously implemented would water demand in 2062 balance to water use levels in 2012. This is the first modeling effort of its kind to examine regional land-use related water demand incorporating historical trends of both developed and agricultural land uses.