Responses and impacts of atmospheric rivers to climate change

Nature Portfolio (Springer Nature) | March 9th, 2020

Atmospheric rivers (ARs) are characterized by intense moisture transport, which, on landfall, produce precipitation which can be both beneficial and destructive. ARs in C

Atmospheric rivers (ARs) are characterized by intense moisture transport, which, on landfall, produce precipitation which can be both beneficial and destructive. ARs in California, for example, are known to have ended drought conditions but also to have caused substantial socio-economic damage from landslides and flooding linked to extreme precipitation. Understanding how AR characteristics will respond to a warming climate is, therefore, vital to the resilience of communities affected by them, such as the western USA, Europe, East Asia and South Africa. In this Review, we use a theoretical framework to synthesize understanding of the dynamic and thermodynamic responses of ARs to anthropogenic warming and connect them to observed and projected changes and impacts revealed by observations and complex models. Evidence suggests that increased atmospheric moisture (governed by Clausius–Clapeyron scaling) will enhance the intensity of AR-related precipitation — and related hydrological extremes — but with changes that are ultimately linked to topographic barriers. However, due to their dependency on both weather and climate-scale processes, which themselves are often poorly constrained, projections are uncertain. To build confidence and improve resilience, future work must focus efforts on characterizing the multiscale development of ARs and in obtaining observations from understudied regions, including the West Pacific, South Pacific and South Atlantic.

Review of Science Used to Estimate Water Supply Reliability Involving the Delta

Delta Stewardship Council (Delta Council) | April 3rd, 2018

Review of Water Supply Reliability Estimation Related to the Sacramento-San Joaquin Delta

Delta Stewardship Council (Delta Council) | June 16th, 2022

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).

Scenarios of Future California Water Demand Through 2050

California Department of Water Resources (DWR) | August 14th, 2014

This paper describes the application of future scenarios for Water Plan Update 2013 (DWR 2013) to quantify future water demand for California and our 10 hydrologic region

This paper describes the application of future scenarios for Water Plan Update 2013 (DWR 2013) to quantify future water demand for California and our 10 hydrologic regions out to the year 2050. Starting with the publication of California Water Plan Update 2005 (DWR 2005), DWR has applied the concept of scenarios to describe future water management conditions. Scenarios are used to capture a broad range of uncertain factors that affect water management that are considered to be beyond the control of water managers. For Update 2013 scenarios were organized around narrative themes of growth and climate change, which were then quantified using factors about future population growth, housing densities, land use patterns, and climate.  For Updates 2005 and 2009, DWR attempted only to quantify future water demand management strategies at the hydrologic region scale. The hydrologic regions are large areas of tens of thousands square miles, too large to compute meaningful information on regional water management actions. But in parallel to the hydrologic region scale analysis as in current Update 2013, DWR has been pursuing a longer term project, to perform a more complete hydrologic analysis at the finer planning area scale. Results and analysis of planning area water management strategies is given in a separate report.  In addition to this paper, background information on the application of scenarios can be found in Chapter 5 and 6 of Update 2013. Chapter 5 provides information how scenarios are used to quantify water management uncertainty. Chapter 6 describes DWR’s efforts to effect long term improvements in data and analytical tools to support the Water Plan. 

Seasonal Peak Snow Predictability Derived From Early-Season Snow in North America

American Geophysical Union (AGU) | September 12th, 2023

Early season snow observations show promise in predicting peak snow water equivalent in locations where large-scale ocean-atmosphere patterns similarly influence fall and

Early season snow observations show promise in predicting peak snow water equivalent in locations where large-scale ocean-atmosphere patterns similarly influence fall and winter conditions, and in northern maritime locations where winter temperatures are warm enough that rain on snow and midwinter melt occur.

Sensitivity of Mountain Hydroclimate Simulations in Variable-Resolution CESM to Microphysics and Horizontal Resolution

American Geophysical Union (AGU) | July 31st, 2018

Sharpening of cold-season storms over the western United States

Nature Portfolio (Springer Nature) | January 19th, 2023

Winter storms are responsible for billion-dollar economic losses in the western United States. Because storm structures are not well resolved by global climate models, it

Winter storms are responsible for billion-dollar economic losses in the western United States. Because storm structures are not well resolved by global climate models, it is not well established how single events and their structures change with warming. Here we use regional storm-resolving simulations to investigate climate change impact on western US winter storms. Under a high-emissions scenario, precipitation volume from the top 20% of winter storms is projected to increase by up to 40% across the region by mid-century. The average increase in precipitation volume (31%) is contributed by 22% from increasing area coverage and 19% from increasing storm intensity, while a robust storm sharpening with larger increase in storm centre precipitation compared with increase in storm area reduces precipitation volume by 10%. Ignoring storm sharpening could result in overestimation of the changes in design storms currently used in infrastructure planning in the region.

Shifts in MJO behavior enhance predictability of subseasonal precipitation whiplashes

Nature Portfolio (Springer Nature) | April 28th, 2025