An Excel Based Module to Explore the Major Drivers of Snowmelt During Rain-On-Snow Flooding Events William Currier, Nic Wayand, & Jessica D. Lundquist *University of Washington, Mountain Hydrology Research, Civil and Environmental Engineering, Seattle, WA, USA Radiometer (CNR4) Introduction: A rain-on-snow flooding event is defined by extreme rain falling Data: Precipitation Gauge over a large extent of a snow-covered basin. Determining the contribution of I. Data to drive the model is taken from various locations: d) snowmelt during these events and determining the primary driver of the snow- 1. The Snoqualmie Pass research station (Figure 3) c) Wind Speed surface energy balance (Figure 1) is a critical question for flood forecasters and is a. Data is archived and available in real time1 2. Three National Resource Conservation Service (NRCS) not well understood due to sparse observations available over complex terrain. Air Temperature/ Existing snow energy balance models used for research are cumbersome to set up SNOTEL RH and run. Therefore, we have developed an Excel energy balance model that is a. Low through high elevation data is provided from the simple to set up, run and modify per the instructors goals. Our target audience is 2009 flood in the Snoqualmie Basin upper-level high school students or entry level undergraduates who have taken a II. Forcing data during different meteorological conditions is physics course and had some exposure to climatology. We include data taken from provided to run this model and includes: the Snoqualmie Pass research station (921 m) and three National Resource a. Air temperature Conservation Service SNOTEL stations in the Snoqualmie basin. The module b. Wind speed contains a PowerPoint presentation, a YouTube video and instructions for a hands c. Relative humidity on lab. The entire module and all of its components can be viewed here. d. Precipitation e. Solar irradiance e) f. Longwave irradiance III. Additional Pacific Northwest Climate projections [Elsener et al. 2010] are provided for students to discuss how changes in mean winter air temperature and precipitation may change rain-on-snow floods in the future. Snoqualmie Pass Figure 3 (Right): a.) The location of Snoqualmie Pass (921 m) relative to the Western U.S. and Canada. b.) The same location overlaid on a DEM. c.) The meteorological tower run by the Washington State Department of Transportation at Snoqualmie Pass d.) The meteorological tower run by the Mountain Hydrology Research group at Snoqualmie Pass. e.) The location of the NRCS SNOTEL stations. The red pixels in (e) show the metropolitan area of Seattle. Lab Exercise: Results/Model Output (Runoff): The model assumes that the temperature In the lab exercise there are instructions on how to run the model for various throughout the snowpack is zero degrees Celsius, therefore any available energy is meteorological conditions. Students are asked various questions such as: used to melt the snowpack. Additionally there is no soil component to the model 1. What components provide the most energy on each type of day? and thus any rainfall is assumed to be available for runoff. The model automatically 2. Comment on the importance of snowmelt vs. rainfall at different elevations during updates it’s figures based on the meteorological conditions allowing the student to the Snoqualmie flood. What is the ratio of snowmelt to rainfall at each elevation? simply and directly receive results from any perturbations in the forcing data. We 3. How could future climate scenarios impact rain-on-snow floods in the Snoqualmie believe this will allow the students to gain a conceptual understanding between Basin and the Pacific Northwest? different meteorological conditions, the resulting energy fluxes and subsequent Figure 1: A simple schematic describing typical rain on snow conditions and the energy balance equation (Red snowmelt. Box). Each component is annotated as follows:, SW – Shortwave Radiation, LW – Longwave Radiation, H – Sensible Heat Flux, Le – Latent Heat Flux, P – Precipitation, G – Ground Head Flux. Results/Model Output (Energy Balance Components): Water Available for Runoff (mm) 250 The model automatically outputs the snow surface energy balance components Goals of the Module: based on the meteorological conditions. Figure 4 shows the resulting daily 200 1. Introduce students to rain-on-snow floods. average net energy balance components available to melt snow based on 150 Typical Spring Day, 2. Provide an interactive environment for students to understand the different meteorological data. The model shows that the turbulent heat fluxes, H Calm Winds energy balance equation and how different components change in and Le, account for 68% of the energy to drive snow melt during a typical rain- 100 2009 Snoqualmie on-snow event while on a typical spring sunny day with calm winds the solar Flood Conditions importance under different meteorological conditions. 50 3. Allow students to discuss and think about how rain-on-snow radiation is the primary driver of snowmelt. 0 Snow Surface Energy balance components. Daily average (Wm-2) events may change in the future. Rainfall Snowmelt Total 100 Figure 5: The water available for runoff (mm) based on the energy balance from the middle elevation station in the Snoqualmie Basin during the 2009 flood and during a typical spring sunny day, with no winds at Snoqualmie Pass. 80 Rain-on-snow flood destruction The most recent rain-on- 60 Additional Resources snow event in the Pacific 40 Northwest was the A YouTube video that briefly introduces the Snoqualmie basin flood in 20 students to the energy balance and rain-on-snow 2009 (Figure 2). 0 flooding is provided. We believe that this could be Net Solar Net Longwave Sensible Heat Latent Heat Flux Heat from Rain Ground Heat assigned as a homework assignment the night Rain on snow floods have caused millions of Flux Flux before. A time-lapse video of the entire 2014 dollars in damages and 2009 Snoqualmie Flood Conditions Typical Spring Day, Calm Winds water year at Snoqualmie Pass is also available Figure 2: Photo (Left) by Alan Berner/Seattle Times on Thursday (January 8, to show the changing conditions at the site. have occurred from the 2009), floodwaters inundate the Snoqualmie Valley. Photo by the Washington Figure 4: A bar chart showing the amount of energy (W m-2) available at the surface based on meteorological conditions Alps to the Western U.S. State Dept. of Transportation of Interstate 5 (Right), south of Seattle closed due at the middle elevation station during the 2009 Snoqualmie Flood and during a typical spring sunny day, with no winds Citations for peer reviewed papers discussing to flooding at Snoqualmie Pass. rain-on-snow events are also available. All model components are available at: http://www.uwpcc.washington.edu/outreach/tertiary.jsp?action=GetEntity&entity=RSF&title=Rain+on+Snow+Flooding+Module 1Archived data: http://depts.washington.edu/mtnhydr/data/snoqualmie.shtml Elsener, M., L. Cuo, N. Voisin, J. Deems, A. Hamlet, J. Vano, K. Mickelson,. S. Lee, D. Lettenmaier, (2010), Implications of 21st century climate change for the hydrology of Washington State. Climatic Change, 1, 225-260 .