Extreme Precipitation & Atmospheric Rivers

A Climatology of Atmospheric Rivers and Associated Precipitation for the Seven US National Climate Assessment Regions

Slinskey, E.A., P.C. Loikith, D.E. Waliser, B. Guan, and A.C. Martin, 2020: A Climatology of Atmospheric Rivers and Associated Precipitation for the Seven U.S. National Climate Assessment Regions. Journal of Hydrometeorology, 21, 2439-2456, https://doi.org/10.1175/JHM-D-20-0039.1.


Personnel

Emily A. Slinskey1, Paul C. Loikith1, Duane E. Waliser2, Bin Guan3, Andrew Martin1

1. Portland State University, Department of Geography, Portland, OR

2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

3. Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles

Figure 1. The seven National Climate Assessment (NCA) sub-regions across the Continental United States and the associated abbreviations.

Project Synopsis

Atmospheric Rivers (ARs) are long, narrow filamentary corridors of enhanced water vapor transport. They play an important role in regional water supply and hydrometeorological extremes. Enhanced precipitation occurs when the AR interacts with a mechanism capable of lifting the AR beyond the saturation level. Here an AR detection algorithm is applied to global reanalysis from Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) to objectively and consistently characterize ARs regionally across the Continental United States (CONUS). This work was completed in support of the ongoing efforts of the National Climate Assessment (NCA) and discusses results relative to the seven NCA delineated regions spanning the CONUS illustrated in Figure 1.

The seasonal distribution of AR frequency, calculated at each grid cell as the percentage of days when the grid cell is within the boundary of an AR for that season, across the CONUS is shown in Figure 2. Results show that along the West Coast and in the Pacific Northwest ARs are primarily a cold season phenomena, with maxima in the winter in the Southwest and in the winter and fall in the Pacific Northwest. East of the Rocky Mountains, AR frequency maxima occur across the seasonal cycle notably in the winter in the southeast, in the spring in the southern Great Plains, and in the fall in the Midwest and Northeast.

Figure 2. AR frequency (% of days) between 1981-2016 at each grid cell. Results are for (a) December, January, and February; (b) March, April, and May; (c) June, July, and August; and (d) September, October, and November.

How often is extreme precipitation associated with atmospheric rivers?

Figure 3. AR extreme precipitation fraction (% of days) calculated as the number of linked 95th percentile extreme precipitation AR days relative to the total number of 95th percentile extreme precipitation days between 1981-2016 at each grid cell. Results are for (DJF) December, January, and February; (MAM) March, April, and May; (JJA) June, July, and August; and (SON) September, October, and November.

The seasonal distribution of the fraction of linked AR extreme precipitation days relative to the total number of extreme precipitation days calculated at each grid cell is shown in Figure 3. ARs represent an important meteorological mechanism for generating wintertime precipitation extremes along the US West Coast. In the eastern and central US, AR fractions are highest in the winter, spring, and fall with several regions revealing noticeable maxima, including the Ohio River Valley. In the Southeast, elevated AR extreme precipitation fractions occur during the non-summer months where winter and spring events across the western portion of the region are linked to strong synoptic weather systems transporting water vapor from the Gulf of Mexico.

Presentations with Published Abstracts

Climate Change Effects on Atmospheric Rivers over the Continental United States. Emily Slinskey (poster), Paul Loikith, Ilan Gonzalez-Hirshfeld, Alexander Goodman, Duane Waliser, Bin Guan, and Andrew Martin. American Meteorological Society Annual Meeting, Virtual, January 2021.


An Assessment of the Contribution of Non-Orographic Lifting in Atmospheric River

Precipitation. Emily Slinskey (poster), Paul Loikith, Ilan Gonzalez-Hirshfeld, Duane Waliser, Bin Guan, and Andrew Martin. American Geophysical Union Fall Meeting, Virtual, December 2020.


Climate Change Effects on Atmospheric Rivers over the Continental United States. Emily Slinskey (talk), Paul Loikith, Ilan Gonzalez-Hirshfeld, Alexander Goodman, Duane Waliser, Bin Guan, and Andrew Martin. International Atmospheric River Community Virtual Symposium, October 2020.

A Climatology of Atmospheric Rivers and Associated Precipitation for the Seven US National Climate Assessment Regions. Emily Slinskey (talk), Paul Loikith, Duane Waliser, Bin Guan, and Andrew Martin. 100th American Meteorological Society Annual Meeting, Boston, Massachusetts, January 2020.

A Climatology of Atmospheric Rivers and Associated Precipitation for the Seven US National Climate Assessment Regions. Emily Slinskey, Paul Loikith (talk), Duane Waliser, Bin Guan, and Andrew Martin. American Geophysical Union Fall Meeting, San Francisco, California, December 2019.

A Climatology of Atmospheric Rivers and Associated Heavy Precipitation over the Northwest United States. Emily Slinskey(talk), Paul Loikith, Duane Waliser, Bin Guan, and Andrew Martin. 10th Annual Northwest Climate Conference, Portland, OR, October 2019.

The Association Between Atmospheric Rivers and Extreme Precipitation over the Eastern United States. Emily Slinskey (talk), Paul Loikith, Duane Waliser, and Bin Guan. American Meteorological Society Annual Meeting, Phoenix, AZ, January 2019.

An Extreme Precipitation Categorization Scheme and its Observational Uncertainty over the Continental United States

Slinskey, E.A., P.C. Loikith, D.E. Waliser, and A. Goodman, 2019: An Extreme Precipitation Categorization Scheme and its Observational Uncertainty over the Continental United States. J. Hydrometeor., 20, 1029–1052, https://doi.org/10.1175/JHM-D-18-0148.1.

Personnel

Emily A. Slinskey1, Paul C. Loikith1, Duane E. Waliser2, Alexander Goodman2

1. Portland State University, Department of Geography, Portland, OR

2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

Figure 1. Precipitation Category (P-Cat) thresholds and associated colors.

Project Synopsis

Extreme precipitation is associated with numerous societal and environmental impacts across the United States (US). According to the 2017 4th National Climate Assessment (NCA), climate change is projected to alter the frequency, severity, and seasonality of extreme precipitation across the US. Therefore, a spatial understanding and intuitive means of monitoring and tracking extreme precipitation over time is critical. Towards this end, we apply an event-based categorization scheme, which assigns Precipitation Categories (P-Cats) to extreme precipitation events based on 3-day storm totals, to demonstrate its utility in interpreting extreme precipitation climatology, variability, and change over space and time. To further constrain observational uncertainty when monitoring and tracking precipitation extremes, the scheme is used as the basis for a dataset intercomparison spanning a range of gridded and in-situ products.

Figure 2. Maximum observed P-Cats at each grid point for 1998-2015. (Top Row) Maximum P-Cats on native grid; (Bottom Row) maximum P-Cats on common MERRA-2 grid. Color scale is as in Figure 1. Un-shaded grid cells indicate that no P-Cat has occurred during the data record.

Figure 2 results show a prevalence of high-end P-Cats in the West across the coastal mountain ranges, the Sierra Nevada and Cascade ranges, and the Transverse Ranges of Southern California. High-end P-Cats also occur in the Southeast stretching from Texas eastward to the Carolinas. The maximum P-Cats recorded during this period are generally much lower across the Great Plains, the desert Southwest, and the interior western rain shadows. All datasets capture this general pattern, however, considerable differences are apparent in P-Cat extent and magnitude. Higher resolution datasets, PRISM and TRMM, most closely resemble GHCN-D and capture a greater frequency of high-end P-Cats relative to the lower resolution products. When all datasets are rescaled to a common coarser grid, differences persist with datasets originally constructed at a high resolution maintaining a higher frequency and magnitude of P-Cats.

Presentations with Published Abstracts

Assessment of Observational Uncertainty in Extreme Precipitation Events over the Continental United States. Emily Slinskey (talk), Paul Loikith, Duane Waliser, and Alexander Goodman. 8th GEWEX Open Science Conference: Extremes and Water on the Edge, Canmore, Alberta, Canada, May 2018.

Assessment of Observational Uncertainty in Extreme Precipitation Events over the Continental United States. Emily Slinskey (poster), Paul Loikith, Duane Waliser, and Alexander Goodman. American Geophysical Union Fall Meeting, New Orleans, LA, December 2017.

A Multi-Platform Dataset Assessment of Observational Uncertainty in Extreme Precipitation Events over the Continental United States. Emily Slinskey (talk), Paul Loikith, Duane Waliser, and Alexander Goodman. American Meteorological Society Conference on Climate Variability and Change, Baltimore, MD, July 2017.

Towards an Event Based Indicator for Monitoring Change in Extreme Precipitation in Support of the US National Climate Assessment. Emily Slinskey, Paul Loikith (poster), Duane Waliser, and Alexander Goodman. American Meteorological Society Annual Meeting, Seattle, WA, January 2017.

Towards an Event Based Indicator for Monitoring Change in Extreme Precipitation in Support of the US National Climate Assessment. Emily Slinskey (poster), Paul Loikith, Duane Waliser, and Alexander Goodman. American Geophysical Union Fall Meeting, San Francisco, CA, December 2016.

Towards an Event Based Indicator for Monitoring Change in Extreme Precipitation in Support of the US National Climate Assessment. Emily Slinskey (poster), Paul Loikith, Duane Waliser, and Alexander Goodman. Association of Pacific Coast Geographers, Portland, OR, October 2016.