Rainfall analysis of the May 2021 southeastern Texas and southern Louisiana flood

ABSTRACT

This paper analyzes the heavy rainfall on 16–20 May 2021 across southeastern Texas and southern Louisiana. In Louisiana, five fatalities were attributed to the event and > $1 billion in losses. The rainfall was caused by two slow-moving, mesoscale convective vortices that concentrated precipitation south of Port Arthur, TX, Lake Charles, LA, and Baton Rouge, LA, in 6 to 12-hour periods. Using calibrated radar data, the Storm Precipitation Analysis System estimated 6-h rainfall totals of 254–362 mm south of Lake Charles, surpassing 200–500-year average recurrence intervals (ARI) for those locations, with an isolated area receiving 367.5 mm, equating to a > 800-year ARI. In East Baton Rouge Parish, LA, 203–268 mm was estimated in 6-h (200–500-year ARI), with an isolated area receiving 274 mm, equivalent to a 750-year ARI. A comparison of the May 2021 and August 2016 events, which both affected southern Louisiana, is made using a depth-area-duration analysis. While the forcing mechanisms differed, 1–6 h rainfall depths were similar at 1 –25,900 km². The May 2021 event exceeded rainfall depths produced by the August 2016 event for 2–6 h durations for area sizes of 1–388 km², highlighting the precipitation intensity produced by the May 2021 event.

KEYWORDS:

• Extreme precipitation
• depth-area-duration
• average recurrence interval

Acknowledgments

VMB, BDK, DTT, and AKS would like to acknowledge support from NOAA Grants NA21OAR4310290 and NA21OAR4310306

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data used in this work is publicly available. Rainfall data are assimilated from six sources Automated Weather Observing Systems, Weather-Bureau-Army-Navy or WBAN, Cooperative Observer Network, Community Collaborative Rain, Hail, & Snow Network, Calcasieu Parish Police Jury’s Alert System – One Rain (58 stations), and Jefferson County (Texas) Drainage District No.6. Average recurrence intervals are from NOAA Atlas 14 and 5-min NEXRAD (Level II) Base Reflectivity Mosaics were downloaded from Iowa State University.

Additional information

Funding

The work was supported by the Climate Program Office [NA21OAR4310290, NA21OAR4310306].