Relative Humidity Has Uneven Effects on Shifts From Snow to Rain Over the Western U.S.

Harpold, Adrian A.; Rajagopal, S.; Crews, J. B.; Winchell, Taylor; Schumer, R.

doi:10.1002/2017gl075046

Cited by 49 publications

(39 citation statements)

References 30 publications

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“…Figure shows that the declining trends in annual maximum M _ only (not including ROS) were higher and more widespread than the other three W conditions with the inclusion of ROS, indicating that annual maximum M _ ros was less likely to be affected by a warming climate. These results were expected because a warming climate can cause more precipitation to fall as rain and partially offset the loss of snowpack (Musselman et al, ), especially in the regions that experience higher humidity and warmer wet bulb temperatures (Harpold et al, ; Rupp & Li, ). In Figures S6–S7, higher humidity is associated with larger annual maximum M _ ros across all SNOTEL stations, highlighting the importance of humidity in controlling the precipitation phase and, consequently, affecting the ROS intensity.…”

Section: Discussionmentioning

confidence: 94%

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

Yan

Sun

Wigmosta

et al. 2019

Geophysical Research Letters

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This paper presents the first study to identity, in historical records, regional changes in the mechanisms of extreme water available for runoff (W). We used a quality‐controlled Snowpack Telemetry data set (1979–2017) combined with the nonparametric regional Kendall test to examine changes in annual maximum W under four hydrometeorological conditions (melt only/rain‐on‐snow/all melt/all melt plus rainfall) over the mountainous regions of the western United States. Under a warming climate, our analyses indicated significant declining trends in annual maximum W at regional scale under all four conditions. The annual maximum of all melt plus rainfall decreased significantly by 15% in the southwestern United States, while the frequency of rain‐on‐snow events increased significantly by 32% in the northwestern United States. The annual maximum snowmelt only decreased significantly by 21% across the entire western United States. Our results confirmed that interaction between regional humidity and solar radiation with warming temperature helps drive these changes.

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Section: Discussionmentioning

confidence: 94%

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

Yan

Sun

Wigmosta

et al. 2019

Geophysical Research Letters

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“… Greater sensitivity to errors associated with the temperature‐only precipitation partitioning method (Harpold, Kaplan, et al, ; Jennings et al, ; Wayand et al, ). Improvement can be made by incorporating wet bulb temperature, dew point temperature, or relative humidity into the partitioning method (Ding et al, ; Harpold, Rajagopal, et al, ; Jennings et al, ; Marks et al, ). Greater sensitivity to errors in model simulated energy balances (Essery et al, ; Lapo et al, ). For instance, although mountain microclimate simulation model algorithms perform reasonably well under most climate conditions, they produce significantly higher (negative) bias in shortwave fluxes and (positive) longwave fluxes in coastal maritime environments (Bohn et al, ; Currier et al, ).…”

Section: Resultsmentioning

confidence: 99%

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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“…The snow‐covered season is the continuous period between initial snow cover and end of season snow disappearance that spans the date of maximum annual SWE. We make no effort to distinguish precipitation phase because of the challenges of doing so without local measurements (Harpold et al, ) of temperature and its relationship to phase (Rajagopal & Harpold, ). Moreover, we were not able to distinguish between melt and rain on days where both may have occurred and thus assumed that all rainwater was stored long enough on the pillow to be recorded (i.e., rain did not drain directly to the soil surface).…”

Section: Data Sets and Methodsmentioning

confidence: 99%

Potential for Changing Extreme Snowmelt and Rainfall Events in the Mountains of the Western United States

Harpold

Kohler

2017

JGR Atmospheres

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The intensity of mountain precipitation is often modified by snow accumulation and melt, yet rainfall‐based observations are widely used in planning and design. Comparisons of extreme rainfall versus snowmelt intensities are needed because they have different predictability and hazard implications. Regional warming is expected to intensify not only rainfall and snowfall but also slow snowmelt, which could further challenge intensity duration frequency (IDF) techniques. We use observations from 379 mountain sites across the western U.S. to estimate the 10 and 100 year intensity at 1, 2, and 30 day durations for historical snowmelt (SM), precipitation occurring during snow cover (SCP), and precipitation during the snow‐free period (SFP). At 1 day durations, 100 year SCP was greater than SM and SFP at 40% of sites, while SM was larger than SCP and SFP at 39% of sites. At 30 day durations, SM was greater than SCP and SFP at 95% of sites. The continental sites are generally insensitive to increased water input intensity from SCP occurring as rainfall. In contrast, the maritime mountains are relatively insensitive to changes in SM but have the potential for increased water input intensity from greater SCP occurring as rainfall. Standard precipitation intensity data sets accurately estimated the 100 year, 1 day SCP and SM but underestimated SM at 78 continental sites where SM was greater than SCP and SFP. These results confirm that snow processes modify IDF estimates and highlight regional sensitivity to increased winter rainfall and slower snowmelt that may necessitate local adaptation strategies.

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Relative Humidity Has Uneven Effects on Shifts From Snow to Rain Over the Western U.S.

Cited by 49 publications

References 30 publications

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

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

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

Potential for Changing Extreme Snowmelt and Rainfall Events in the Mountains of the Western United States

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