Observed Spatiotemporal Changes in the Mechanisms of Extreme Water Available for Runoff in the Western United States

Yan, Hongxiang; Sun, Ning; Wigmosta, Mark S.; Skaggs, Richard L.; Leung, L. Ruby; Coleman, André M.; Hou, Zhangshuan

doi:10.1029/2018gl080260

Cited by 30 publications

(32 citation statements)

References 50 publications

(81 reference statements)

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“…Figures 9a and 9b. The largest increases in the western United States occur in the high-elevation mountains that have not been affected by ROS in the past, especially the Upper Cascades in the PNW, which is consistent with the finding in Yan et al (2019). The greatest decreases occur in the coastal western United States, especially the middle-and low-elevation west facing barriers of the Sierra Nevada and the Cascades, where declines in snow accumulation and increases in rainfall intensity (which dilute ROS runoff contribution ratio) will occur in the future.…”

Section: Water Resources Researchsupporting

confidence: 89%

The Role of Rain‐on‐Snow in Flooding Over the Conterminous United States

Lettenmaier

Margulis

et al. 2019

Water Resources Research

111

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Based on a process‐level modeling of the rain‐on‐snow (ROS) events in the period of 1950 to 2013 and in a warmer climate, we quantify the historical and future runoff contribution from ROS to extreme floods and the source of runoff and snowmelt in large ROS events within the conterminous United States (CONUS). We find that the regions impacted most heavily by ROS include the West Coast, the major mountain ranges of the western interior, the Upper Midwest, the Northeast, and the lower Appalachians. While 70% of extreme (upper 0.1%) runoff events in these regions have some contribution from ROS, the runoff generated during these ROS events accounts for less than 10% of the total extreme flood runoff; the much larger fraction of extreme runoff is from either intense rainfall or clear‐sky snowmelt. Rainfall is the dominant source of runoff in ROS events along the West Coast and over the west‐facing slopes of the Cascades and Sierra Nevada, while snowmelt dominates ROS runoff in the other regions in the CONUS. Net radiation dominates the snowmelt during ROS in the high mountains in the West, while net radiation and turbulent heat flux are equally dominant in the rest of CONUS. Historically, the role of ROS in streamflow extremes is most significant in midelevation areas, but this “significant influence zone” will shift to higher elevations in a warmer future. The future ROS frequency changes exert a first order control on the future change of the runoff contribution from ROS to extreme floods.

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Section: Water Resources Researchsupporting

confidence: 89%

The Role of Rain‐on‐Snow in Flooding Over the Conterminous United States

Lettenmaier

Margulis

et al. 2019

Water Resources Research

111

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“…Berghuijs et al () explored the dominant flood‐generating mechanisms across the continental United States and found that snowmelt and ROS events were more robust predictors of the flooding response than rainfall over the western United States. This is further confirmed by Yan et al (), Yan, Sun, Wigmosta, Skaggs, Leung, et al () who found that the standard precipitation‐based intensity‐duration‐frequency curves often significantly underestimate extreme events in snow‐dominated environments, suggesting a critical role of snow in flooding in those environments. With a warming climate, ROS‐driven flood risk is projected to increase significantly in many western United States river basins with more frequent ROS events at high elevations where seasonal snowpack persists even in a warmer climate (Musselman et al, ).…”

Section: Introductionsupporting

confidence: 65%

Regional Snow Parameters Estimation for Large‐Domain Hydrological Applications in the Western United States

et al. 2019

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In snow‐dominated regions, a key source of uncertainty in hydrologic prediction and forecasting is the magnitude and distribution of snow water equivalent (SWE). With ensemble simulations, this work demonstrates that SWE variability across the mountain ranges of the western United States (represented by 246 Snow Telemetry stations) can largely be captured at the daily time scale by a simple mass and energy‐balance snow model with four physically reasonable parameters—three snow albedo parameters and one snow temperature threshold for precipitation partitioning. The model skill is lower in the maritime Pacific Northwest where SWE variability is more sensitive to errors associated with simulated energy balance (e.g., downward radiation fluxes) and the temperature‐only precipitation partitioning approach. Poor model skill in high‐altitude, windy locations in the Northern Rockies can be attributed to precipitation undercatch and underrepresented wind processes. For the purpose of large‐domain hydrologic applications, regional snow parameters were developed for eight ecoregions characterized by a distinct hydroclimatic regime across the western United States. Results suggest that regionally coherent snow parameterizations are able to capture daily variations in SWE at most Snow Telemetry stations, suggesting that areas with a similar hydroclimate share a similar snow regime. While the three albedo parameters show limited spatial variability across all regions, the regional snow temperature threshold (Ts) shows marked spatial variation correlated with relative humidity; the Ts values increase from 0.2 °C in the higher‐humidity Pacific Northwest to 4.0 °C in the colder, lower‐humidity Rocky Mountains.

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“…By differentiating the precipitation phase using the change in SWE, the authors (Yan et al, 2018) also identified the dominant mechanism of extreme W at these sites, and found significant regional differences in flood-generating mechanisms across the WUS, e.g., the maritime regime is ROS dominated, and the continental regime is snowmelt dominated. The authors (Yan et al, 2019b) confirmed that this regional variability is associated with climate variability across the WUS, which includes air temperature, solar radiation, and atmospheric humidity. In the maritime regime that features high humidity, latent energy can warm the falling precipitation through condensation, leading to more frequent ROS events (Harpold and Brooks, 2018).…”

Section: Ng-idf Curves Vs Prec-idf Curvesmentioning

confidence: 64%

“…Global warming will lead to a shift in rain-snow ratio and increase soil freeze-thaw cycles, resulting in more frequent ROS events and higher flood risk at higher elevations in the future (Beniston and Stoffel, 2016;Musselman et al, 2018;Li et al, 2019). Using the BCQC SNOTEL data, the authors (Yan et al, 2019b) examined the changes in snow process and frequency of ROS events over 1979-2017. They found statistically significant trends toward declining and earlier snowmelt over the WUS.…”

Section: Nonstationary Ng-idf Curves Under Climate Changementioning

confidence: 99%

Next-Generation Intensity-Duration-Frequency Curves for Climate-Resilient Infrastructure Design: Advances and Opportunities

et al. 2020

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National and international security communities (e.g., U.S. Department of Defense) have shown increasing attention for innovating critical infrastructure and installations due to recurring high-profile flooding events in recent years. The standard infrastructure design approach relies on local precipitation-based intensity-duration-frequency (PREC-IDF) curves that do not account for snow process and assume stationary climate, leading to high failure risk and increased maintenance costs. This paper reviews the recently developed next-generation IDF (NG-IDF) curves that explicitly account for the mechanisms of extreme water available for runoff including rainfall, snowmelt, and rain-on-snow under nonstationary climate. The NG-IDF curve is an enhancement to the PREC-IDF curve and provides a consistent design approach across rain- to snow-dominated regions, which can benefit engineers and planners responsible for designing climate-resilient facilities, federal emergency agencies responsible for the flood insurance program, and local jurisdictions responsible for developing design manuals and approving subsequent infrastructure designs. Further, we discuss the recent advances in climate and hydrologic science communities that have not been translated into actional information in the engineering community. To bridge the gap, we advocate that building climate-resilient infrastructure goes beyond the traditional local design scale where engineers rely on recipe-based methods only; the future hydrologic design is a multi-scale problem and requires closer collaboration between climate scientists, hydrologists, and civil engineers.

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Observed Spatiotemporal Changes in the Mechanisms of Extreme Water Available for Runoff in the Western United States

Cited by 30 publications

References 50 publications

The Role of Rain‐on‐Snow in Flooding Over the Conterminous United States

The Role of Rain‐on‐Snow in Flooding Over the Conterminous United States

Regional Snow Parameters Estimation for Large‐Domain Hydrological Applications in the Western United States

Next-Generation Intensity-Duration-Frequency Curves for Climate-Resilient Infrastructure Design: Advances and Opportunities

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