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Tuesday, June 5, 2018

NOAA Atlas 14: Updated Rainfall Data Underscore Challenges of Managing Flood Risk

Hurricane Harvey

HARC scientists have been working to compile data about the impacts of flooding in our region.

Written by Carolyn LaFleur, Research Scientist, Energy and Sustainability

We all know that our region is facing enormous challenges as we grapple with flooding. While many factors such as development patterns and climate change affect flood risk, it comes down to how much rainfall we get and how runoff from storm events can be managed. Accurate information on rainfall amounts is essential to address these threats. National Oceanic and Atmospheric Administration (NOAA) scientists are developing revised predictions for major storm events based on historical rainfall data including the record-setting rainfall amounts of Hurricane Harvey. This is part of a national effort to provide a comprehensive atlas of precipitation for storms of various durations and return periods. Known as Atlas 14, this forthcoming NOAA publication contains the latest rainfall data for much of the United States. The Atlas is now the official U.S. Government source of precipitation frequency estimates.

With the benefit of 100 years of historical rainfall data, NOAA scientists formulate predictions on the magnitude of future rainfall events, including the 100-year storm.

With the benefit of 100 years of historical rainfall data, NOAA scientists formulate predictions on the magnitude of future rainfall events, including the 100-year storm. The 100-year storm event represents a 24-hour rainfall event with a 1% probability of occurring in any given year. Similarly, the probability of a 500-year storm event is 0.2%. Historical records, projected trends, and the devastation of recent floods clearly show that change is needed to mitigate future risk. In an update from the NOAA Hydrometeorological Design Studies Center New Atlas 14 data for our region indicate that rainfall amounts for the 100-year storm have significantly increased, by as much as to two to five inches. Some areas could see predicted 24-hour rainfall totals of as much as 14 to 18 inches. NOAA anticipates that the updated Atlas 14 data will be published by September 30th this year.

Rainfall data are used to create maps of flood zones to inform the public about flood risk. The Federal Emergency Management Agency (FEMA) flood hazard mapping program identifies flood hazards, assesses flood risks, and provides information for state and local entities involved in planning, permitting, and mitigation. Information about flood risk can be obtained for a specific site by entering an address in the online tool. Updated rainfall data will require updates for these maps as well. NOAA anticipates that the updated Atlas 14 data will be published by September 30th this year.

HARC scientists have been working to compile data about the impacts of flooding in our region. Using the power of Geographic Information Systems (GIS) in a readily accessible, user-friendly format, HARC published a story map Summarizing Hurricane Harvey's Environmental Impacts soon after the devastating event. HARC continues the work of studying ways in which communities can be made more resilient against future threats from severe weather events and transitional meteorological patterns. Research is essential to better understand existing vulnerabilities and develop adaptive strategies to mitigate damage to homes, businesses, and the environment.

The new rainfall data soon to be published by NOAA will be critical for decisions about land use, infrastructure design, emergency response, and more. As local officials and planners work toward solutions to protect and mitigate property losses, many solutions must be considered. Along with major new conventional infrastructure projects, we need improved development practices that reduce runoff and incorporate green stormwater infrastructure. By conserving and emulating the function of natural systems such as wetlands and riparian corridors we can invoke the sublime efficiency of nature to convey and clean stormwater. We all recognize the need for innovative, resilient structures and energy systems, and changes in how we collectively think about flood risk and response. HARC scientists are engaged in these critical conversations across our region, with independent analysis for people seeking scientific answers.