Archive June 2012

How deep was Wednesday’s snowfall? The people weigh in Waiology Jun 08

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By Daniel Collins

The snowstorm that covered much of the South Island with a white veil on Wednesday cut power to over a thousand homes and closed many schools and businesses. But in the midst of the disruption was a rare opportunity to do some important science: to measure the amount and density of the snow that fell at low elevations.

To get as much of this data as possible we asked for your help, and the results are now in. 42 people, at last count, sent in measurements, from Dunedin to Rangiora; a few more data are to be added.

CitizenSnowData6June2012Here is a Google Map of the measurements we’ve received. Ross Woods has helpfully compiled the largest measured depth at each location submitted.

Sampling is obviously biased towards Christchurch, because that’s where our social and scientist networks are largest. It’s not that snow didn’t fall elsewhere, just that no one there made the measurements for us. (We know it fell widely from aircraft and satellite photos shown in the media.)

The measurements are colour-coded — orange low, yellow intermediate, and blue high. The lowest measurements were near Leeston, Lyttelton and a few places around Christchurch. The highest were on the northern flank of the Port Hills (Christchurch south) and further north in Canterbury. In Christchurch, measurements made of asphalt or the like were shallower than over grass.

The Press explains why just north of Canterbury received the deepest snow.

A few people also made some handy density measurements. 21% in Spreydon (that is, percent relative to that of liquid water), 26% in Sydenham, 15% in Burnside in the morning and than 26% in the evening, and several others. Yes, snow density increased during the day. These numbers are invaluable in estimating snow loading on buildings.

The range of values we see across Christchurch, during the day, and even just a few centimeters apart, tells us that snow depth is quite variable. It is therefore important that we don’t just take one measurement but many. Replication. As we accrue more numbers, we get a richer and more accurate understanding of snowstorms.

And so a big thanks to all those citizen and professional scientists who gathered the data and sent them in. It all helps to push the envelop of hydrological knowledge a little bit further. But winter has just begun, so when it snows, we welcome more of your measurements.

Citizen science: How deep is the snow at your place? Waiology Jun 06


By Daniel Collins and Ross Woods

Measurements of snowfall at low elevations around New Zealand are few and far between, and yet the data would be really helpful in understanding how snowfall occurs and quantifying snow-related risks. After all, the large majority of New Zealand’s population and infrastructure reside closer to the coast than the mountains.

And so we’d like your help.

If you live at an elevation below 400 m, measure the snow depth after it snows. And if you’re extra keen, measure the snow water equivalent too.

Here are the instructions:

  1. Safety first. Do not make any measurements if it puts you or anyone else at risk. Data are valuable, but not that valuable.
  2. Measure the snow depth.
    1. Choose a location. Choose somewhere typical; don’t just focus on deep snow or snow drifts.
    2. Put a ruler vertically into the snow right down to ground level and record the snow depth. Do this 10 times at each location.
    3. Estimate how far apart these points are from one another: it could be just 10 meters or 100 meters, don’t make them further apart than that.
    4. If there are several days of snow, repeat these measurements at the same general location each day during fine spells, not when it’s snowing.
    5. Repeat these measurements at as many locations as you like, but keep the numbers separate.
  3. Measure the snow water equivalent
    1. This measurement tells us how heavy the snow is, or its density. Very handy when estimating snow loadings for buildings.
    2. Choose a location and measure the snow depth following the above instructions.
    3. Find an old saucepan (or similar cylinder) with straight sides, and measure its (inside) diameter
    4. Press the upside-down saucepan vertically down into the snow until you reach the ground (snow may need to be compressed into the pan – that’s ok)
    5. Pick up the saucepan and most of the snow should come with it. Pick up any snow that falls out and put it in the pan.
    6. Slowly melt all the snow in the pan, and measure the volume of water (e.g. with a measuring jug). Take care not to boil off the water.
    7. Repeat this exercise as many times as you’d like, being sure to keep the results distinct.
    8. Record the depth of snow, the diameter of the container, and the volume of melted water. Also record the location (e.g., in my garden or in a park, post code 9999 or street address).
  4. Send us your measurements
    1. For each location, send us your 10 snow depth measurements and whatever snow water equivalent measurements you made. Be sure to include a description of this location (e.g., in my garden, in a park) as well as a post code (address is optional and will be kept confidential).
    2. There are several ways you can send us your measurements:
      1. In the comments below
      2. In an email sent from the Contact page.
      3. In an email to either Daniel Collins or Ross Woods (firstname.surname AT
    3. Be sure to include the location of the measurements and the date and time of observation.
  5. What will happen to the data?
    1. The data will be given to any scientific study that asks for it, excluding your personal details and address.
    2. If we have enough data, we’ll develop a Google Map to share and will post it here on Waiology.

If you’d like to know what the snow density is, here are the equations:

Snow volume (in mL) = pi * ([Diameter in mm]/2)2 * [Depth in mm] / 1000
Snow density (in %) = 100 x [Volume of melted water in mL] / [Volume of snow in mL]

Or if snow depth = 180 mm, pan diameter = 200 mm, and the volume of melted water = 1620 mL, then the snow volume = 3.1416 x (200 / 2)2 * 180 / 1000 = 5655 mL. Snow density = 100 x 1620 / 5655 = 29%.

We look forward to your wonderful, citizen-powered data!

SnowElevation400mUpdate 7:40 pm. If you’re wondering what parts of the South Island, the main recipient of today’s snowfall, is below 400 m in elevation, here you go. (Just disregard the parts of the North Island that you can see.)

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