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Thoughts From Engineers: Precipitation Estimates That Make Us or Break Us

Chris Maeder on February 2, 2023 - in Articles, Column

On the eve of the New Year, in a one-two move suggestive of a “prepper” mentality, the U.S. Congress passed two laws that address the issues of national resilience and disaster preparedness. Sponsors of the legislation noted that the vulnerable state of the country’s infrastructure combined with the frequency of recent extreme storms constituted the principal drivers behind passage of these two significant federal laws.

The sweeping 2021 Infrastructure Investment and Jobs Act (IIJA) set aside funds for rebuilding the nation’s infrastructure and advanced appropriations in the amount of $492 million to the National Oceanic and Atmospheric Administration (NOAA) for a number of water-modeling and flood-mapping initiatives, including updated precipitation studies. The Providing Research and Estimates of Changes in Precipitation (PRECIP Act) was passed to undertake a portion of this critical research. The PRECIP Act draws from funds identified in the IIJA and additional appropriations to research different methodologies and ultimately update extreme precipitation estimates to better reflect current trends and future climate conditions.

The Flood Level Observation, Operations and Decision Support Act (FLOODS Act) calls for development of a national warning and notification system that’s broad in reach, responsive to changing conditions, and agile in its ability to give notice to at-risk parties quickly and efficiently. The FLOODS Act complements the goals of the PRECIP Act in several important ways. Most importantly, both laws are unmistakable signals that the United States is accelerating its work in terms of preparing for climate change.

Designing for Durability: Why Up-to-Date Precipitation Data Is Essential

Precipitation frequency estimates are necessary for critical infrastructure design and development as well as countless other applications such as stormwater management and modeling, floodplain and watershed management, stream-flow analysis, and more. Extreme rainfall estimates, specifically probable maximum precipitation (PMP) estimates, have long been used in the design of critical infrastructure such as dams, bridges, hospitals and power facilities. These data are vital to building resilient infrastructure, and numerous professional groups—from the Association of State Floodplain Management to the American Society of Civil Engineers to the Union of Concerned Scientists—all have voiced strong support for updated PMP estimates.

What Does the PRECIP Act Require?

If there was a way for Congress to focus—laser-like—on the challenge represented by current and future precipitation trends, the PRECIP Act is the answer. NOAA is directed to contract with the National Academies of Sciences, Engineering and Medicine (National Academies) for the purpose of studying the “state of practice and research needs for precipitation estimation, including probable maximum precipitation estimation.”

The National Academies also is specifically charged with assessing methodologies that consider non-stationary conditions in the context of future climate variability. Recommendations for long-term data management, critical areas of research as well as strengthening interagency coordination and partnerships also are required. No later than six years following the completion of the report that covers these topics, NOAA is charged with publishing updated PMPs for the entire United States. Thereafter, the estimates are to be revisited at least every 10 years. The PRECIP Act also mandates development of a National Guidance document that covers best practices for federal and state agencies, consultants, and other users of PMP studies.

Elements of a Comprehensive Flood-Warning System

The FLOODS Act is an ambitious, comprehensive law that establishes a “National Integrated Flood Information System” that builds on existing state, regional and local forecasting; data collection; and information networks; but it also ramps all these systems up a notch. The law calls for more monitoring at critical locations and more-robust lines of communication across and among federal and state agencies as well as other relevant private and public parties. Not only will the system “provide an effective flood early warning system,” it also “collects and integrates information on the key indicators of floods and flood impacts, including streamflow, reservoir release and diversion, precipitation, soil moisture,” and other parameters.

The comprehensive and integrated character of the law’s mandate is apparent in language that calls for “improvements in seasonal precipitation and temperature … and floodwater prediction.” Additional monitoring and observational tools as well as modeling capability are authorized—in fact, anything that NOAA considers necessary—to achieve as completely as possible “total water prediction.” This floodwater monitoring and informational system includes all interconnected and related physical systems, including modeling to “improve the coupling of and interoperability between hydrologic models and coastal ocean models.”

Bringing closure to years of irregular funding and updates via special request from regional sources, the law also provides annual federal funding on the order of $3.5 million each year between 2020 and 2030 for updates to the official NOAA Precipitation Frequency Atlas. The Atlas will publish updated frequency estimates every 10 years and will cover “temporal and spatial distributions of heavy precipitation; analyses of seasonality in precipitation; and trends in annual maximum series data.”

Steps Forward … and Back

Both laws stress research and ongoing investigations of the many questions and challenges identified by the laws. In the case of the FLOODS Act, NOAA must vigilantly evaluate the fitness of the country’s existing warning and notification systems, and remedy any shortcomings. The PRECIP Act calls on NOAA, the National Academies and partner institutions to aggressively examine our understanding of underlying atmospheric and geophysical systems. Both laws ensure NOAA and its partners remain watchful and responsive to changing circumstances moving forward.

As these initiatives roll out on a national scale, local-scale communities freshly hit by extreme precipitation and flooding hunker down and revisit land-use plans, update zoning ordinances and rebuild—drawing on data that aren’t necessarily representative of current or future conditions. The construction industry isn’t waiting for updated precipitation estimates, and county and municipal planning efforts press on as well, often to inadvertently push development into flood-prone areas.

The PRECIP and FLOOD laws represent critical initiatives to ensure state-of-the-art science, research and warning systems are accessible to all—from engineers and contractors to local decision-makers to vulnerable U.S. citizens. The situation is far from perfect, particularly from a timing perspective. The fire has been lit, and the momentum to prepare, warn and build to withstand extreme weather events is accelerating, but a country as complex, multi-layered and diverse as the United States can only move so fast. 


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About Chris Maeder

Chris Maeder, P.E., M.S., CFM, is engineering director at CivilGEO Inc.; email: [email protected].

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