scholarly journals Diagnosing Moisture Sources for Flash Floods in the United States. Part I: Kinematic Trajectories

2019 ◽  
Vol 20 (8) ◽  
pp. 1495-1509 ◽  
Author(s):  
Jessica M. Erlingis ◽  
Jonathan J. Gourley ◽  
Jeffrey B. Basara
Keyword(s):  
United States ◽  
Flash Flood ◽  
The United States ◽  
Flash Floods ◽  
Reanalysis Data ◽  
Front Range ◽  
Flow Paths ◽  
South Central ◽  
Central Texas ◽  
Regional Reanalysis

Abstract This study uses backward trajectories derived from North American Regional Reanalysis data for 19 253 flash flood reports during the period 2007–13 published by the National Weather Service to assess the origins of air parcels for flash floods in the conterminous United States. The preferred flow paths for parcels were evaluated seasonally and for six regions of interest: the West Coast, Arizona, the Front Range of the Rocky Mountains, Flash Flood Alley in south-central Texas, the Missouri Valley, and the Appalachians. Parcels were released from vertical columns in the atmosphere at times and locations where there were reported flash floods; these were traced backward in time for 5 days. The temporal and seasonal cycles of flood events in these regions are also explored. The results show the importance of trajectories residing for long periods over oceanic regions such as the Gulf of Mexico and the Caribbean Sea. The flow is generally unidirectional with height in the lower layers of the atmosphere. The trajectory paths from oceanic genesis regions to inland hotspots and their orientation with height provide clues that can assist in the diagnosis of impending flash floods. Part II of this manuscript details the land–atmosphere interactions along the trajectory paths.

Changes in Future Flash Flood–Producing Storms in the United States

2020 ◽  
Vol 21 (10) ◽  
pp. 2221-2236 ◽  
Author(s):  
Erin Dougherty ◽  
Kristen L. Rasmussen
Keyword(s):  
United States ◽  
Climate Models ◽  
Flash Flood ◽  
Global Climate ◽  
The United States ◽  
Flash Floods ◽  
Global Climate Models ◽  
Future Climate ◽  
South Central ◽  
Rain Rates

AbstractFlash floods are high-impact events that can result in massive destruction, such as the May 2010 flash floods in the south-central United States that resulted in over $2 billion of damage. While floods in the current climate are already destructive, future flood risk is projected to increase based on work using global climate models. However, global climate models struggle to resolve precipitation structure, intensity, and duration, which motivated the use of convection-permitting climate models that more accurately depict these precipitation processes on a regional scale due to explicit representation of convection. These high-resolution convection-permitting simulations have been used to examine future changes to rainfall, but not explicitly floods. This study aims to fill this gap by examining future changes to rainfall characteristics and runoff in flash flood–producing storms over the United States using convection-permitting models under a pseudo–global warming framework. Flash flood accumulated rainfall increases on average by 21% over the United States in a future climate. Storm-generated runoff increases by 50% on average, suggesting increased runoff efficiency in future flash flood–producing storms. In addition to changes in nonmeteorological factors, which were not explored in this study, increased future runoff is possible due to the 7.5% K−1 increase in future hourly maximum rain rates. Though this median change in rain rates is consistent with Clausius–Clapeyron theory, some storms exhibit increased future rain rates well above this, likely associated with storm dynamics. Overall, results suggest that U.S. cities might need to prepare for more intense flash flood–producing storms in a future climate.

scholarly journals Diagnosing Moisture Sources for Flash Floods in the United States. Part II: Terrestrial and Oceanic Sources of Moisture

2019 ◽  
Vol 20 (8) ◽  
pp. 1511-1531 ◽  
Author(s):  
Jessica M. Erlingis ◽  
Jonathan J. Gourley ◽  
Jeffrey B. Basara
Keyword(s):  
United States ◽  
Boundary Layer ◽  
Land Surface ◽  
Flash Flood ◽  
The United States ◽  
Flash Floods ◽  
Heat Fluxes ◽  
Surface Model ◽  
Positive Anomaly ◽  
The Impact

Abstract Backward trajectories were derived from North American Regional Reanalysis data for 19 253 flash flood reports published by the National Weather Service to determine the along-path contribution of the land surface to the moisture budget for flash flood events in the conterminous United States. The impact of land surface interactions was evaluated seasonally and for six regions: the West Coast, Arizona, the Front Range, Flash Flood Alley, the Missouri Valley, and the Appalachians. Parcels were released from locations that were impacted by flash floods and traced backward in time for 120 h. The boundary layer height was used to determine whether moisture increases occurred within the boundary layer or above it. Moisture increases occurring within the boundary layer were attributed to evapotranspiration from the land surface, and surface properties were recorded from an offline run of the Noah land surface model. In general, moisture increases attributed to the land surface were associated with anomalously high surface latent heat fluxes and anomalously low sensible heat fluxes (resulting in a positive anomaly of evaporative fraction) as well as positive anomalies in top-layer soil moisture. Over the ocean, uptakes were associated with positive anomalies in sea surface temperatures, the magnitude of which varies both regionally and seasonally. Major oceanic surface-based source regions of moisture for flash floods in the United States include the Gulf of Mexico and the Gulf of California, while boundary layer moisture increases in the southern plains are attributable in part to interactions between the land surface and the atmosphere.

scholarly journals Evaluation of Tools Used for Monitoring and Forecasting Flash Floods in the United States

2012 ◽  
Vol 27 (1) ◽  
pp. 158-173 ◽  
Author(s):  
Jonathan J. Gourley ◽  
Jessica M. Erlingis ◽  
Yang Hong ◽  
Ernest B. Wells
Keyword(s):  
United States ◽  
Flash Flood ◽  
The United States ◽  
Flash Floods ◽  
Urban Setting ◽  
Flash Flooding ◽  
Flood Prediction ◽  
Critical Success ◽  
Monitoring And Forecasting ◽  
First Time

Abstract This paper evaluates, for the first time, flash-flood guidance (FFG) values and recently developed gridded FFG (GFFG) used by the National Weather Service (NWS) to monitor and predict imminent flash flooding, which is the leading storm-related cause of death in the United States. It is envisioned that results from this study will be used 1) to establish benchmark performance of existing operational flash-flood prediction tools and 2) to provide information to NWS forecasters that reveals how the existing tools can be readily optimized. Sources used to evaluate the products include official reports of flash floods from the NWS Storm Data database, discharge measurements on small basins available from the U.S. Geological Survey, and witness reports of flash flooding collected during the Severe Hazards Analysis and Verification Experiment. Results indicated that the operational guidance values, with no calibration, were marginally skillful, with the highest critical success index of 0.20 occurring with 3-h GFFG. The false-alarm rates fell and the skill improved to 0.34 when the rainfall was first spatially averaged within basins and then reached 50% of FFG for 1-h accumulation and exceeded 3-h FFG. Although the skill of the GFFG values was generally lower than that of their FFG counterparts, GFFG was capable of detecting the spatial variability of reported flash flooding better than FFG was for a case study in an urban setting.

Real-Time Flash Flood Forecasting

2018 ◽  
Author(s):  
Jonathan J. Gourley ◽  
Robert A. Clark
Keyword(s):  
United States ◽  
Real Time ◽  
Flash Flood ◽  
Weather Prediction ◽  
The United States ◽  
Flood Forecasting ◽  
Flash Floods ◽  
Hydrologic Model ◽  
The World ◽  
Flash Flood Forecasting

Flash floods are one of the world’s deadliest and costliest weather-related natural hazards. In the United States alone, they account for an average of approximately 80 fatalities per year. Damages to crops and infrastructure are particularly costly. In 2015 alone, flash floods accounted for over $2 billion of losses; this was nearly half the total cost of damage caused by all weather hazards. Flash floods can be either pluvial or fluvial, but their occurrence is primarily driven by intense rainfall. Predicting the specific locations and times of flash floods requires a multidisciplinary approach because the severity of the impact depends on meteorological factors, surface hydrologic preconditions and controls, spatial patterns of sensitive infrastructure, and the dynamics describing how society is using or occupying the infrastructure. Real-time flash flood forecasting systems rely on the observations and/or forecasts of rainfall, preexisting soil moisture and river-stage states, and geomorphological characteristics of the land surface and subsurface. The design of the forecast systems varies across the world in terms of their forcing, methodology, forecast horizon, and temporal and spatial scales. Their diversity can be attributed at least partially to the availability of observing systems and numerical weather prediction models that provide information at relevant scales regarding the location, timing, and severity of impending flash floods. In the United States, the National Weather Service (NWS) has relied upon the flash flood guidance (FFG) approach for decades. This is an inverse method in which a hydrologic model is run under differing rainfall scenarios until flooding conditions are reached. Forecasters then monitor observations and forecasts of rainfall and issue warnings to the public and local emergency management communities when the rainfall amounts approach or exceed FFG thresholds. This technique has been expanded to other countries throughout the world. Another approach, used in Europe, relies on model forecasts of heavy rainfall, where anomalous conditions are identified through comparison of the forecast cumulative rainfall (in space and time) with a 20-year archive of prior forecasts. Finally, explicit forecasts of flash flooding are generated in real time across the United States based on estimates of rainfall from a national network of weather radar systems.

scholarly journals Flood Fatalities in the United States

2008 ◽  
Vol 47 (3) ◽  
pp. 805-818 ◽  
Author(s):  
Sharon T. Ashley ◽  
Walker S. Ashley
Keyword(s):  
United States ◽  
Hurricane Katrina ◽  
Flood Control ◽  
The United States ◽  
Ohio River ◽  
Structural Modifications ◽  
South Central ◽  
Central Texas ◽  
And Gender ◽  
Social Vulnerabilities

Abstract This study compiles a nationwide database of flood fatalities for the contiguous United States from 1959 to 2005. Assembled data include the location of fatalities, age and gender of victims, activity and/or setting of fatalities, and the type of flood events responsible for each fatality report. Because of uncertainties in the number of flood deaths in Louisiana from Hurricane Katrina, these data are not included in the study. Analysis of these data reveals that a majority of fatalities are caused by flash floods. People between the ages of 10 and 29 and >60 yr of age are found to be more vulnerable to floods. Findings reveal that human behavior contributes to flood fatality occurrences. These results also suggest that future structural modifications of flood control designs (e.g., culverts and bridges) may not reduce the number of fatalities nationwide. Spatially, flood fatalities are distributed across the United States, with high-fatality regions observed along the northeast Interstate-95 corridor, the Ohio River valley, and near the Balcones Escarpment in south-central Texas. The unique distributions found are likely driven by both physical vulnerabilities for flooding as well as the social vulnerabilities.

scholarly journals The Flashiest Watersheds in the Contiguous United States

2015 ◽  
Vol 16 (6) ◽  
pp. 2365-2381 ◽  
Author(s):  
Brianne K. Smith ◽  
James A. Smith
Keyword(s):  
United States ◽  
Pacific Northwest ◽  
West Coast ◽  
Urban Areas ◽  
Flash Flood ◽  
The United States ◽  
Flood Damage ◽  
Flood Events ◽  
Discharge Data ◽  
South Central

Abstract The authors identify the flashiest watersheds in the contiguous United States based on frequency of discharge peaks exceeding 1 m3 s−1 km−2. The entire digitized record of USGS instantaneous discharge data is used for all stream gauging stations with over 10 years of data. Using the 1 m3 s−1 km−2 threshold, the flashiest basins in the contiguous United States are located in urban areas along a swath of states from the south-central United States to the mid-Atlantic and in mountainous areas of the West Coast, especially the Pacific Northwest. The authors focus on small watersheds to identify the flashiest cities and states across the country and find Tulsa, Oklahoma; Baltimore, Maryland; and St. Louis, Missouri, to be the flashiest cities in the contiguous United States. Thunderstorms are major agents for peak-over-threshold flood events east of the Rocky Mountains, and tropical cyclones play a secondary role, especially in the Southeast. West Coast flood events are associated with winter storms. Flooding west of and within the Rockies is linked to steeply sloped terrain and compact watersheds. East of the Rockies, urban areas dominate flashy watersheds. The authors find that watersheds northeast (downwind) of city centers are flashier than other urban watersheds, consistent with the downwind maximum in rainfall found in many urban regions. They examine anomalous flood response in the Illinois–Missouri region; St. Louis is among the flashiest cities in the United States, while Chicago is among the least flashy. Their flashiness map is compared with other measures of flooding, including flood damage and National Weather Service flash flood reports.

Variations in Flash Flood-Producing Storm Characteristics Associated with Changes in Vertical Velocity in a Future Climate in the Mississippi River Basin

2021 ◽  
Author(s):  
Erin Dougherty ◽  
Kristen L. Rasmussen
Keyword(s):  
United States ◽  
River Basin ◽  
Vertical Velocity ◽  
Mississippi River ◽  
Flash Flood ◽  
The United States ◽  
Flash Floods ◽  
Future Climate ◽  
Mississippi River Basin ◽  
Storm Characteristics

AbstractThe Mississippi River Basin (MRB) is a flash flood hotspot receiving the most frequent flash floods and highest average rainfall accumulation of any region in the United States. Given the destruction flash floods cause in the current climate in the MRB, it is critical to understand how they will change in a future, warmer climate in order to prepare for these impacts. Recent work utilizing convection-permitting climate simulations to analyze future precipitation changes in flash flood-producing storms in the United States shows that the MRB experiences the greatest future increase in flash flood rainfall. This result motivates the goal of the present study to better understand the changes to precipitation characteristics and vertical velocity in flash flood-producing storms in the MRB. Specifically, the variations in flash flood-producing storm characteristics related to changes in vertical velocity in the MRB are examined by identifying 484 historical flash flood-producing storms from 2002–2013 and studying how they change in a future climate using 4-km convection-permitting simulations under a pseudo-global warming framework. In a future climate, precipitation and runoff increase by 17% and 32%, respectively, in flash flood-producing storms in the MRB. While rainfall increases in all flash flood-producing storms due to similar increases in moisture, it increases the most in storms with the strongest vertical velocity, suggesting that storm dynamics might modulate future changes in rainfall. These results are necessary to predict and prepare for the multifaceted impacts of climate change on flash flood-producing storms in order to create more resilient communities.

scholarly journals Extreme Precipitation Events in the South-Central United States during May and June 2010: Historical Perspective, Role of ENSO, and Trends

2011 ◽  
Vol 12 (5) ◽  
pp. 1056-1070 ◽  
Author(s):  
R. W. Higgins ◽  
V. E. Kousky ◽  
P. Xie
Keyword(s):  
United States ◽  
Daily Precipitation ◽  
Flash Flood ◽  
The United States ◽  
Flood Events ◽  
The South ◽  
South Central ◽  
Extreme Precipitation Events ◽  
Central United States ◽  
Precipitation Events

Abstract An analysis of extreme daily precipitation events that occurred in the south-central United States during May and June 2010 is carried out using gridded station data and reanalysis products in use at the National Centers for Environmental Prediction (NCEP). Various aspects of the daily extremes are examined from a climate perspective using a 62-yr (1948–2010) period of record, including their historical ranking, common circulation features, moisture plumes, and the possible influence of ENSO. The analysis also considers how the frequency and intensity of daily extremes is changing in the United States. Each of the 2010 flash flood events examined here was associated with historic daily rainfall totals. Several of the events had meteorological conditions in common at upper and lower levels of the atmosphere, and all of the events fit well into an existing classification scheme for heavy precipitation events associated with flash flooding. Each case exhibited characteristics of the “Maya Express” flood events that link tropical moisture plumes from the Caribbean and Gulf of Mexico to midlatitude flooding over the central United States. Consistent with recent assessment reports, it is shown that extreme daily precipitation events in the United States have increased in frequency during the most recent 30-yr period (1980–2009) when compared to the previous 30-yr period (1950–79), though the increases are relatively small during May and June.

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