Evaluation of the subseasonal forecast skill of floods associated with atmospheric rivers in coastal Western U.S. watersheds

2021 ◽  
Author(s):  
Qian Cao ◽  
Shraddhanand Shukla ◽  
Michael J. DeFlorio ◽  
F. Martin Ralph ◽  
Dennis P. Lettenmaier
Keyword(s):  
River Basin ◽  
West Coast ◽  
Forecast Skill ◽  
Probabilistic Forecast ◽  
Lead Times ◽  
Flood Events ◽  
Streamflow Prediction ◽  
Antecedent Soil Moisture ◽  
Atmospheric Rivers ◽  
The U.S

AbstractAtmospheric rivers (ARs) are responsible for up to 90% of major flood events along the U.S. West Coast. The timescale of subseasonal forecasting (two weeks to one month) is a critical lead time for proactive mitigation of flood disasters. The NOAA/Climate Testbed Subseasonal Experiment (SubX) is a research-to-operations project with almost immediate availability of forecasts. It has produced a reforecast database that facilitates evaluation of flood forecasts at these subseasonal lead times. Here, we examine the SubX driven forecast skill of AR-related flooding out to 4-week lead using the Distributed Hydrology Soil Vegetation Model (DHSVM), with particular attention to the role of antecedent soil moisture (ASM), which modulates the relationship between meteorological and hydrological forecast skill. We study three watersheds along a transect of the U.S. West Coast: the Chehalis River basin in Washington, the Russian River basin in Northern California, and the Santa Margarita River basin in Southern California. We find that the SubX driven flood forecast skill drops quickly after week 1, during which there is relatively high deterministic forecast skill. We find some probabilistic forecast skill relative to climatology as well as ensemble streamflow prediction (ESP) in week 2, but minimal skill in weeks 3-4, especially for annual maximum floods, notwithstanding some probabilistic skill for smaller floods in week 3. Using ESP and reverse-ESP experiments to consider the relative influence of ASM and SubX reforecast skill, we find that ASM dominates probabilistic forecast skill only for small flood events at week 1, while SubX reforecast skill dominates for large flood events at all lead times.

A Summary of GFS Ensemble Integrated Water Vapor Transport Forecasts and Skill Along the U.S. West Coast during Water Years 2017–2020

2021 ◽  
Author(s):  
Jason M. Cordeira ◽  
F. Martin Ralph
Keyword(s):  
Water Vapor ◽  
West Coast ◽  
Situational Awareness ◽  
Probability Of Detection ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
Lead Times ◽  
Atmospheric Rivers ◽  
Skill Scores ◽  
The U.S

AbstractThe ability to provide accurate forecasts and improve situational awareness of atmospheric rivers (ARs) is key to impact-based decision support services and applications such as forecast-informed reservoir operations. The purpose of this study is to quantify the cool-season water year skill for 2017–2020 of the NCEP Global Ensemble Forecast System forecasts of integrated water vapor transport along the U.S. West Coast commonly observed during landfalling ARs. This skill is summarized for ensemble probability-over-threshold forecasts of integrated water vapor transport magnitudes ≥250 kg m–1 s–1 (referred to as P250). The P250 forecasts near North-Coastal California at 38°N, 123°W were reliable and successful at lead times of ~8–9 days with an average success ratio >0.5 for P250 forecasts ≥50% at lead times of 8 days and Brier skill scores >0.1 at a lead time of 8–9 days. Skill and accuracy also varied as a function of latitude and event characteristics. The highest (lowest) success ratios and probability of detection values for P250 forecasts ≥50% occurred on average across northern California and Oregon (southern California), whereas the average probability of detection of more intense and longer duration landfalling ARs was 0.1–0.2 higher than weaker and shorter duration events at lead times of 3–9 days. The potential for these forecasts to enhance situational awareness may also be improved, depending on individual applications, by allowing for flexibility in the location and time of verification; the success ratios increased 10–30% at lead times of 5-to-10 days allowing for flexibility of ±1.0° latitude and ±6 hours in verification.

scholarly journals Floods due to Atmospheric Rivers along the U.S. West Coast: The Role of Antecedent Soil Moisture in a Warming Climate

2020 ◽  
Vol 21 (8) ◽  
pp. 1827-1845 ◽  
Author(s):  
Qian Cao ◽  
Alexander Gershunov ◽  
Tamara Shulgina ◽  
F. Martin Ralph ◽  
Ning Sun ◽  
...  
Keyword(s):  
Soil Moisture ◽  
River Basin ◽  
West Coast ◽  
Extreme Precipitation ◽  
Antecedent Soil Moisture ◽  
Extreme Precipitation Events ◽  
Warming Climate ◽  
The U.S ◽  
Precipitation Events

AbstractPrecipitation extremes are projected to become more frequent along the U.S. West Coast due to increased atmospheric river (AR) activity, but the frequency of less intense precipitation events may decrease. Antecedent soil moisture (ASM) conditions can have a large impact on flood responses, especially if prestorm precipitation decreases. Taken together with increased antecedent evaporative demand due to warming, this would result in reduced soil moisture at the onset of extreme precipitation events. We examine the impact of ASM on AR-related floods in a warming climate in three basins that form a transect along the U.S. Pacific Coast: the Chehalis River basin in Washington, the Russian River basin in Northern California, and the Santa Margarita River basin in Southern California. We ran the Distributed Hydrology Soil Vegetation Model (DHSVM) over the three river basins using forcings downscaled from 10 global climate models (GCMs). We examined the dynamic role of ASM by comparing the changes in the largest 50, 100, and 150 extreme events in two periods, 1951–2000 and 2050–99. In the Chehalis basin, the projected fraction of AR-related extreme discharge events slightly decreases. In the Russian basin, this fraction increases, however, and more substantially so in the Santa Margarita basin. This is due to increases in AR-related extreme precipitation events, as well as the fact that the relationship of extreme precipitation to extreme discharge is strengthened by projected increases in year-to-year volatility of annual precipitation in California, which increases the likelihood of concurrent occurrence of large storms and wet ASM conditions.

scholarly journals Forecasting Atmospheric Rivers during CalWater 2015

2017 ◽  
Vol 98 (3) ◽  
pp. 449-459 ◽  
Author(s):  
Jason M. Cordeira ◽  
F. Martin Ralph ◽  
Andrew Martin ◽  
Natalie Gaggini ◽  
J. Ryan Spackman ◽  
...  
Keyword(s):  
Water Vapor ◽  
West Coast ◽  
Heavy Precipitation ◽  
Field Studies ◽  
Field Phase ◽  
Forecast System ◽  
Field Campaign ◽  
Atmospheric Rivers ◽  
Vapor Flux ◽  
The U.S

Abstract Atmospheric rivers (ARs) are long and narrow corridors of enhanced vertically integrated water vapor (IWV) and IWV transport (IVT) within the warm sector of extra tropical cyclones that can produce heavy precipitation and flooding in regions of complex terrain, especially along the U.S. West Coast. Several field campaigns have investigated ARs under the CalWater program of field studies. The first field phase of CalWater during 2009–11 increased the number of observations of precipitation and aerosols, among other parameters, across California and sampled ARs in the coastal and near-coastal environment, whereas the second field phase of CalWater during 2014–15 observed the structure and intensity of ARs and aerosols in the coastal and offshore environment over the northeast Pacific. This manuscript highlights the forecasts that were prepared for the CalWater field campaign in 2015, and the development and use of an “AR portal” that was used to inform these forecasts. The AR portal contains archived and real-time deterministic and probabilistic gridded forecast tools related to ARs that emphasize water vapor concentrations and water vapor flux distributions over the eastern North Pacific, among other parameters, in a variety of formats derived from the National Centers for Environmental Prediction (NCEP) Global Forecast System and Global Ensemble Forecast System. The tools created for the CalWater 2015 field campaign provided valuable guidance for flight planning and field activity purposes, and they may prove useful in forecasting ARs and better anticipating hydrometeorological extremes along the U.S. West Coast.

scholarly journals The role of nearshore air-sea interactions for landfalling atmospheric rivers on the U.S. West Coast

2021 ◽  
Author(s):  
Samuel T Bartusek ◽  
Hyodae Seo ◽  
Caroline C Ummenhofer ◽  
John Steffen
Keyword(s):  
West Coast ◽  
Atmospheric Rivers ◽  
The U.S

scholarly journals Hourly storm characteristics along the U.S. West Coast: Role of atmospheric rivers in extreme precipitation

2017 ◽  
Vol 44 (13) ◽  
pp. 7020-7028 ◽  
Author(s):  
M. A. Lamjiri ◽  
M. D. Dettinger ◽  
F. M. Ralph ◽  
Bin Guan
Keyword(s):  
West Coast ◽  
Extreme Precipitation ◽  
Atmospheric Rivers ◽  
Storm Characteristics ◽  
The U.S

scholarly journals The Role of Nearshore Air‐Sea Interactions for Landfalling Atmospheric Rivers on the U.S. West Coast

2021 ◽  
Vol 48 (6) ◽  
Author(s):  
Samuel T. Bartusek ◽  
Hyodae Seo ◽  
Caroline C. Ummenhofer ◽  
John Steffen
Keyword(s):  
West Coast ◽  
Atmospheric Rivers ◽  
The U.S

scholarly journals Changes in the Climatology, Structure, and Seasonality of Northeast Pacific Atmospheric Rivers in CMIP5 Climate Simulations

2017 ◽  
Vol 18 (8) ◽  
pp. 2131-2141 ◽  
Author(s):  
Michael D. Warner ◽  
Clifford F. Mass
Keyword(s):  
Water Vapor ◽  
West Coast ◽  
Large Scale ◽  
Coupled Model ◽  
Water Vapor Transport ◽  
Atmospheric Rivers ◽  
Climate Simulations ◽  
Rcp 8.5 ◽  
Intercomparison Project ◽  
The U.S

Abstract This paper describes changes in the climatology, structure, and seasonality of cool-season atmospheric rivers influencing the U.S. West Coast by examining the climate simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) that are forced by the representative concentration pathway (RCP) 8.5 scenario. There are only slight changes in atmospheric river (AR) frequency and seasonality between historical (1970–99) and future (2070–99) periods considering the most extreme days (99th percentile) in integrated water vapor transport (IVT) along the U.S. West Coast. Changes in the 99th percentile of precipitation are only significant over the southern portion of the coast. In contrast, using the number of future days exceeding the historical 99th percentile IVT threshold produces statistically significant increases in the frequency of extreme IVT events for all winter months. The peak in future AR days appears to occur approximately one month earlier. The 10-model mean historical and end-of-century composites of extreme IVT days reflect canonical AR conditions, with a plume of high IVT extending from the coast to the southwest. The similar structure and evolution associated with ARs in the historical and future periods suggest little change in large-scale structure of such events during the upcoming century. Increases in extreme IVT intensity are primarily associated with integrated water vapor increases accompanying a warming climate. Along the southern portion of the U.S. West Coast there is less model agreement regarding the structure and intensity of ARs than along the northern portions of the coast.

scholarly journals CalWater Field Studies Designed to Quantify the Roles of Atmospheric Rivers and Aerosols in Modulating U.S. West Coast Precipitation in a Changing Climate

2016 ◽  
Vol 97 (7) ◽  
pp. 1209-1228 ◽  
Author(s):  
F. M. Ralph ◽  
K. A. Prather ◽  
D. Cayan ◽  
J. R. Spackman ◽  
P. DeMott ◽  
...  
Keyword(s):  
West Coast ◽  
New Technologies ◽  
Weather Prediction ◽  
Cloud Microphysics ◽  
Global Climate Models ◽  
Climate Projections ◽  
Atmospheric Rivers ◽  
Changing Climate ◽  
New Findings ◽  
The U.S

Abstract The variability of precipitation and water supply along the U.S. West Coast creates major challenges to the region’s economy and environment, as evidenced by the recent California drought. This variability is strongly influenced by atmospheric rivers (ARs), which deliver much of the precipitation along the U.S. West Coast and can cause flooding, and by aerosols (from local sources and transported from remote continents and oceans) that modulate clouds and precipitation. A better understanding of these processes is needed to reduce uncertainties in weather predictions and climate projections of droughts and floods, both now and under changing climate conditions. To address these gaps, a group of meteorologists, hydrologists, climate scientists, atmospheric chemists, and oceanographers have created an interdisciplinary research effort, with support from multiple agencies. From 2009 to 2011 a series of field campaigns [California Water Service (CalWater) 1] collected atmospheric chemistry, cloud microphysics, and meteorological measurements in California and associated modeling and diagnostic studies were carried out. Based on the remaining gaps, a vision was developed to extend these studies offshore over the eastern North Pacific and to enhance land-based measurements from 2014 to 2018 (CalWater-2). The dataset and selected results from CalWater-1 are summarized here. The goals of CalWater-2, and measurements to date, are then described. CalWater is producing new findings and exploring new technologies to evaluate and improve global climate models and their regional performance and to develop tools supporting water and hydropower management. These advances also have potential to enhance hazard mitigation by improving near-term weather prediction and subseasonal and seasonal outlooks.

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