There is a strong relationship between BC's weather in winter and spring and the state of the El Niño Southern Oscillation (ENSO) and this relationship translates to variability in the province's snowpack from year to year. This app allows the exploration of that relationship between snow accumulation and ENSO in the province of British Columbia.
Snow water equivalent stations are maintained and operated by the [BC Ministry of Environment and Climate Change Strategy] (https://www2.gov.bc.ca/gov/content/environment/air-land-water/water/water-science-data/water-data-tools/snow-survey-data) and its partners BC Hydro, Rio Tinto, and Metro Vancouver. Data are collected using instruments called snow pillows which weigh the overlying snow and that weight is converted to the water equivalent content of the snowpack. Data are daily and comprise a daily archive through the previous water year (2023 at the time of this app's creation) and the continuously updated daily data for the most recent water year. The current-year snow data may have quality artifacts because the data have not been quality controlled. Oceanic Niño Index (ONI) is produced by the US National Oceanic and Atmospheric Administration's [Climate Prediction Center] (https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php). The index is based on sea surface temperature anomalies in the Niño 3.4 region of the tropical Pacific Ocean.
The primary elements of the plot are median snow water equivalent grouping by day of the hydrological year and range about that median expressed as one standard deviation of the data for that hydrological day. A trace and range are shown for each of the full record (in grey) and for the record subset by the selected ENSO strength colorized with reds showing selections with ENSO positive (El Niño) overall and blues for selections with ENSO negative (La Niña). For example, if the ONI range is -0.5 to 2, the midpoint of the range is 1.25 and thus the plot of the subset will be red in color.
The Oceanic Niño Index for a given year is taken as the extrema for the winter season of interest. The underlying ONI data are over three-month periods and incorporate the seasons OND through MAM. Rules for the hydrological year are applied. So, for example, if the extrema of the ONI falls in either the OND or NDJ seasons of the year 2005, the ascribed year will be 2006. The slider element of the app is labelled with subjective ENSO strengths. These are mapped to ONI as follows:
- -0.5 to 0.5 is ENSO neutral
- -1.3 or 1.3 are mapped as moderate events
- -2.7 or 2.7 are mapped as extreme events.
ONI is resolved and may be selected at 0.1 degree increments.
The data from the individual years are presented as-is. As described above, the current year's data is likely to have spurious values that have not been corrected by quality control software.
The primary component of this webpage is a graph that depicts the evolution of accumulated snow amount over the water year that runs from 1 October through 30 September in the subsequent year. User controls are:
- a checklist in the upper left to subset data to that with current year data and that with more than 20 years;
- a slider in the upper right that allows for the selection of a range of values of the ENSO strength;
- a map that shows the location of snow-pillow sites in BC;
- a graph that plots the snow water equivalent for the hydrological year.
The checklist contains two items whose selection causes the stations available for plotting to be subset. By default, the Require current year? option is selected to show stations that have data for the current year. The second option allows the restriction of available data to those stations with 20 or more years of record. Furthermore, a station is considered to have data for a given year only if the timeseries more than 80% complete. These longer, more complete records are recommended for investigating the ENSO/snow relationship for a given station.
The slider allows for the selection of a range of values of the ENSO strength as determined by the Oceanic Niño Index. Click and drag the handles or click on the slider bar and the range will adjust to your input. The graph title will respond and show you the currently selected ONI range. To view the entirety of the data for the chosen station, select the extreme ends of the range slider to encompass all ENSO conditions.
To select a station, zoom in to a station symbol of interest and click on it. The click will cause the graph to plot the data for that station and highlight the station in red. There are four button controls in the upper right corner of the map that allow downloading an image of the current map, zooming in, zooming out or resetting the axes.
What is plotted on the graph is dictated by the other app elements and can also be controlled by interacting with the two legends. The legend in the upper-left of the plot controls the presentation of the median and range curves for the station. The legend below the graph's axes controls the plotting of individual years. Clicking on a legend entry turns the element on or off. Double clicking turns all elements on or all but the clicked entry off. Finally, the graph and maps can both be zoomed into to modify the range of what is plotted. Additional controls in the upper right of the graph alow one to download an image of the current plot, reset the axes or choose a graph selection method.
This tool is intended for educational or entertainment purposes only. Official analysis of the snow and water supply status for British Columbia is available from the BC River Forecast Centre. The author makes no warranty nor is liable for anything associated with or resulting from the use of the app or the underlying data. No claims for data correctness or accuracy are made. This application is not affiliated with the Government of British Columbia, BC Hydro, Rio Tinto or Metro Vancouver.
Faron Anslow [email protected]