Canada’s Only True Desert

The media, governments, and tourism marketers have long been promoting the South Okanagan region around Osoyoos, BC, as Canada’s only true desert — even though Osoyoos is only semi-arid (or semi-desert if you prefer). As we shall see below, it is not a “true desert” by any known scientific definition.


Osoyoos, British Columbia

Others have tried this type of scam before, but few with the success of Osoyoos.

One tourist website I stumbled across a number of years ago started out by admitting that Lillooet (another semi-arid town) receives about 330 mm (13 inches) of precipitation per year at the official weather station, but then went on to claim that other areas of the valley where no weather stations have ever existed actually received less than 50 mm (2 inches). Don’t ask me how they would know that when no one was measuring it. Anyway, this would surely put the town in desert territory since  North America’s driest location — Death Valley, California — receives more than that. It seems that cooler heads have prevailed because this “information” has been scrubbed from the internet.

Inaccurate statistics placed on the internet become stubborn obstacles to truth long after they’ve been thoroughly debunked. One example being Della Falls on Vancouver Island, which has long been known as Canada’s tallest waterfall. Even a government website listed it as such until recently when some waterfall enthusiasts measured the waterfall. This bogus statistic is slowing being scrubbed from the internet and from government sources, but the misinformation lingers in the minds of the public.

Back to “Canada’s only true desert” again. In the old days – say like five years ago – you’d find a lot more articles like this, this, and this. Yes, you read that last story right – they actually claim there are tarantulas living there, which, of course, is complete horsefeathers! Equally false is the statement about the area being part of the Sonoran Desert. Not to be outdone, even the federal and provincial governments got into the act calling this area part of the Great Basin Desert.

Today the articles and press releases seem more nuanced, calling Osoyoos desert-like instead of “Canada’s only true desert.” I can only assume it’s because someone has asked tough questions like the waterfall enthusiasts did around Della Falls. Still, the public is left in the dark because any sort of correction has been done quietly to save face.


Those claims that Osoyoos is Canada’s only true desert and the northern extent of the Sonoran Desert are surprisingly easy to falsify.  The Sonoran Desert doesn’t even make it half way up Nevada, so that’s easy to debunk, but desert does exist into Washington State, and as we will see shortly, into British Columbia as well – just not Osoyoos.

The accepted definition of a desert is an area where the aridity index is less than 0.2 (think of it as evaporation being five times higher than precipitation); this index is calculated by taking the precipitation and dividing it by the potential evapotranspiration (similar to evaporation).

Desert (arid) is one of four dry climate classifications, accounting for 47% of the planet’s landmass.


Several different methods and formulas exist for determining the aridity. The best one is the Penman-Monteith method because it takes into account variables such as wind, humidity, sunshine, and air pressure.

Let’s look at the formula for a second.


Ahhh. Okay, let’s move on.

Less sophisticated methods are more often used to estimate potential evapotranspiration because the only variables available for most places are temperature and precipitation.

One of the more popular methods for determining aridity is the one employed by the Köppen climate classification. I will spare you the formula, but it yields similar results, placing Osoyoos in the wetter half of the semi-arid category. The Penman-Monteith method yields a more arid result, but at just over 0.28, still lands solidly within the semi-arid zone.

You might be saying to yourself at this point that Osoyoos might not be a true desert, but it’s the most arid place in Canada. After all, aridity is a function of both temperature and precipitation, and Osoyoos is both hot and dry. Temperature is an important component of aridity which is why Tuscon, Arizona is much more arid than Barrow, Alaska despite the fact that it gets more precipitation.

Similarly, Osoyoos is more arid than the far north for the same reason, but Osoyoos is not the most arid place in British Columbia. This alone surprises people who have been brainwashed into believing that Osoyoos is the driest place in Canada. Places drier than Osoyoos in Canada include the prairies around Medicine Hat, Kamloops, Merritt, Spences Bridge, the Fraser Canyon north of Lillooet, and parts of the Chilcotin from Kleena Kleene to the Fraser river. Drier (less precipitation), but not necessarily more arid.

The driest place of all is Ashcroft, which averages just over 200 mm (8″) per year. By comparison, Osoyoos averages 323 mm (12.7″) per year. This is a substantial inequality that the marginal temperature difference cannot overcome.

Using either of the methods above places Ashcroft in the arid category. The graph below shows the aridity of various places in Canada using the Penman-Monteith method.


The Köppen climate classification also locates Ashcroft in the arid or desert category, and this  map on Wikipedia confirms that.

So it is true that true desert exists in Canada, but it’s located 230 km to the northwest of Osoyoos in the village of Ashcroft. That’s why aliens, when they choose to visit us, crash in the Ashcroft area, and as we all know, UFOs always crash in “true deserts.” The X-files has documented such an event recently near Ashcroft.

xfiles1 xfiles2 xfiles3

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11 Responses to Canada’s Only True Desert

  1. John says:

    How can you say that Ashcroft has an arid or desert climate and averages just over 200mm a year when there isn’t a climate station there to give us this information?

    • Hi John, Ashcroft has had several weather stations over the years, covering 70 years from 1924 to the present. The current automated weather station has been in operation since 2010 with precipitation data missing until 2014. Similarly, Osoyoos has had several weather stations over the years from 1954 to the present, for a total of 62 years. The only weather station in operation today is the automated station which has been in operation since 1990, though it didn’t start recording precipitation with any sort of accuracy until recently.

      That’s the downside of modern automated weather stations tasked with measuring precipitation — they are notoriously inaccurate and subject to frequent errors and missing data points. That’s why precipitation is derived from the abandoned manual stations while wind and humidity data are extracted from the automated station for both Osoyoos and Ashcroft.

      In 2010, an automated weather station was also installed at Ashcroft. This is interesting, not only because it is the first time since 1989 that weather data is available for that village, but also because it is the first time that wind speed and humidity have been measured. If you recall, these two variables are needed in order to accurately calculate aridity. In addition, we need daily minimum and maximum temperature, hours of sunshine, and precipitation.

      The problem with this new station – like so many automated weather stations today – is that it has a lot of missing precipitation data. The other hole in our data set is the hours of sunshine. I figure that since Ashcroft is between 25 and 30% drier than Kamloops, it would be a safe to add 5% to the Kamloops numbers as a means of estimating Ashcroft.

      Using the past two years of data along with this sunshine estimate, I arrived a number very similar to Kamloops as far as Potential Evapo-Transpiration (PET) level. While Ashcroft gets more sunshine, and more temperature extremes, the higher windspeeds at Kamloops balances out the evaporation rate difference.

      Using the data and assumptions above, the PET for Ashcroft is 974.5mm of evaporation/year, so aridity comes down to dividing the actual precipitation by this number.

      Since we have little precipitation data in Ashcroft since the 1980s, we can deduce a number from older data.

      Looking at EC database, we observe the following data sets:

      Ashcroft = 187.0 mm ( 31 years between 1924 and 1970)
      Ashcroft = 206.3mm (6 years between 1973 and 1980)
      Ashcroft North = 209.7 mm (5 years between 1980 and 1985)

      Of course, precipitation is a huge factor when determining aridity, so I spent time time trying various ways of accurately calculating this figure.

      Method #1: Obtaining a weighted average, we get 192.7 mm/year.
      Aridity Index = 0.1977; Status: arid, but barely

      Method #2: Compare the data from the 70s and 80s to Kamloops and scale to today’s levels: 204.8 mm
      Aridity Index = 0.21; Status: semi-arid

      Method #3: Use the data from the 1924-1970 (when BC was much drier than it is today): 187 mm
      Aridity Index = 0.19; Status: arid.

      Method #4: Using the Köppen climate classification method (google it to see how it works). According this data as shown on the Köppen climate classification map, Ashcroft is a true desert even using the figure arrived at in method #2 above.

      So it’s not 100% certain that Ashcroft is a true desert, but it is by far the driest place in BC, and thus the most arid and desert-like place in the province. The second most arid place in BC is Spences Bridge, which I left off the chart for simplicity sake.

  2. John says:

    Thanks for the detailed reply. You’ve done a good job at trying to get the most out of the limited data available. I’m glad to hear that a new climate station has been installed there.

    What I’m really intersted to know is how does one view the old climate station data for Ashcroft?

  3. Pingback: The Sunshine Tax | Questioning The Data

  4. Roger says:

    Now I will have to stop telling people I have been to the northern most desert in the world, based on the aridity index, referring to Carcross Desert, Yukon. Off to Ashcroft to re-establish my credibility. Thanks for the info..

  5. Les Robertson says:

    you might check Empress Alberta its drier then Osoyoos just a bit more precip. then Ashcroft but more sun and wind a higher evaporation rate summer heat too

    • Empress is slightly less arid than Medicine Hat even though it’s slightly drier. The reason being that it’s colder. Temperature is a large factor with evaporation. So is wind, but so is relative humidity, and BC has significantly drier air than Alberta during the summer months. As for sunshine, Alberta is sunny in the winter, but BC is just as sunny during the summer months, and that’s when it has the largest impact on aridity.

      Note that Empress gets 311.6mm/year while Ashcroft gets just over 200mm. That’s a significant difference that can’t easily be overcome by other factors like wind.

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