Climate change already has begun altering hydrologic cycles around the world, and it will continue to influence water quality and water quantity, the latter not only in terms of annual means but also seasonal trends, extremes, and transitions from snow to rain. The preceding changes in precipitation regimes combined with land cover and land use changes will alter runoff patterns. Changes in precipitation and runoff will in turn influence the resilience and functionality of the natural and built infrastructure on which the Department of Defense (DoD) depends to fulfill its missions and stewardship requirements.

In particular, stormwater and flood management infrastructures are commonly designed to handle specific design storms derived from at-site historical rainfall intensity-duration-frequency (IDF) curves. These curves are based on the assumptions that rainfall patterns and distributions are (1) spatially similar within a drainage area and (2) will remain unchanged throughout the design lifetimes of the infrastructures. Non-stationary conditions of land cover/land use and climate change challenge these assumptions. In 2015 SERDP began funding a cohort of projects that will improve our understanding of how precipitation and its variability and runoff may change with time and location and how these changes will affect DoD’s ability to ensure its infrastructure remains resilient in a changing world.

Dr. Dennis Lettenmaier of the University of California, Los Angeles and his project team, under SERDP project RC-2513, are studying how engineering design criteria for flooding and extreme precipitation, from snowmelt and rain-on-snow events, can be adjusted to reflect observed and projected effects of climate change. The new design criteria will be consistent with standard engineering practice, but take into account the evolving effects of climate change. This work will directly benefit risk-based flood design on DoD facilities.

Under SERDP project RC-2514, Dr. Yonas Demissie of Washington State University and his project team will develop an innovative framework that integrates methodologies for regional, adaptive, and probabilistic estimation of rainfall and runoff IDF curves, taking into consideration the spatial variation of precipitation in drainage areas and impacts of future climate change and uncertainty. The framework will be applied to 13 DoD installations across different geographic and climate regions to assess the potential risk of severe storms and resulting floods to existing installations. This research will result in novel approaches for developing next-generation IDF curves.

Dr. Anna Wagner of the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory and her project team, under SERDP project RC-2515, are working to improve understanding of snow accumulation and associated runoff timing, intensity, duration, and long-term trends as affected by a changing climate. This project will investigate historic and future climate scenarios at regional and watershed scales during snowmelt events and produce associated IDF curves for each of the study locations. These updated IDF curves will help DoD to define the impacts of climate change and develop adaptation strategies when changing snow conditions are involved.

Under SERDP project RC-2516, Dr. Casey Brown of the University of Massachusetts and his project team are developing and evaluating methods to produce updated IDF curves for engineering design at DoD installations. This research will couple non-stationary statistical analyses of observed hydrologic extremes with climate information produced through Earth system modeling. The resulting statistical framework will project future extremes and provide guidance on the use of historical and projection-based climate information to inform engineering design and management processes.

Dr. Kenneth Kunkel of North Carolina State University and his project team, under SERDP project RC-2517, are developing a framework for incorporating the potential impact of future climate change into IDF values of heavy precipitation. This project will leverage previous work conducted by the research team on heavy precipitation events. Actual changes in IDF values result from changes in atmospheric capacity (water vapor concentrations) and opportunity (the number and intensity of heavy precipitation-producing storm systems). This project will evaluate these two components to determine the potential impact for a wide range of frequencies and durations used by civil engineers. It also will provide a means for adjusting and delivering the IDF values and uncertainty estimates, similar to the National Oceanic and Atmospheric Administration (NOAA) Atlas 14.

For more information on these projects, visit SERDP and ESTCP’s Climate Change – Vulnerability and Impact Assessment sub-program area.