Kelowna IS Semi-Arid?

[Glacier]

Somewhat related to this thread: Okanagan Lake evaporation factor

a three-year, $3 million project that looked at the valley’s water supply, but found one piece of the puzzle missing: how much water is lost off Okanagan Lake through evaporation?

Initial estimates put lake evaporation at one metre per year.

Using the aridity indexes for Penticton that I calculated on the previous page, we can expect an evaporation rate of 0.98 m per year. It's good to know that EC agrees with me.

[BriTer]

I haven't read this whole thread so I don't know if anyone has mentioned yet that we are part of the Sonora Desert system. The only desert in Canada.

[oneh2obabe]

Canada has only one officially, recognized desert. It lies in the southern part of British Columbia's Okanagan Valley, near the town of Osoyoos.

Nowhere in Canada is there a desert, at least not in the way most people mean "desert". The badlands of Alberta are located within the semi-arid western prairies, and as such, cannot be deserts. Dry they are, but not dry enough to be a desert. The Okanagan Valley contains no deserts. Places in the Okanagan, such as Osoyoos, like the western prairies, are semi-arid, and again do not in any way comprise a desert. Osoyoos may "officially" be called a desert, however this is not based on any ecological standing, and it is likely that Osoyoos is called a desert for tourism reason. Parts of the far north are considered to be "polar deserts", as they receive very little precipitation, but most people do not use the word 'desert" to refer to such places.

[Glacier]

Canada has only one officially, recognized desert.

To be clear, Osoyoos is not an officially recognized desert. It's simply a marketing term used by local tourism promoters that has caught on within the general public. It's akin to how Lytton calls itself "Canada's Hotspot" even though there is no scientific basis to the claim. Such claims are pure marketing (AKA propaganda).

Everyone needs their claim to fame. The truth is secondary.

[oneh2obabe]

You know that, I know that, but we can't make everybody believe it. But it does make for a good marketing ploy doesn't it? This was in the 2nd part of my post and they note that Osoyoos is called a desert for tourism reasons.

The Okanagan Valley contains no deserts. Places in the Okanagan, such as Osoyoos, like the western prairies, are semi-arid, and again do not in any way comprise a desert. Osoyoos may "officially" be called a desert, however this is not based on any ecological standing, and it is likely that Osoyoos is called a desert for tourism reason.

[Glacier]

Exciting stuff! I think I may have just proved that there IS a true desert in BC, or last there used to be 50 to 100 years ago.

In 2010, a weather station was installed at Ashcroft. This is interesting, not only because it is the first time since 1985 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 doesn't record precipitation. 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 things out.

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 no idea how much precipitation has fallen in Ashcroft since 1985, 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 1912 and 1970)
Ashcroft = 206.3mm (6 years between 1973 and 1980)
Ashcroft North = 209.7 mm (5 years between 1980 and 1985)

The big question remains: Is Ashcroft arid or semi-arid? Before we attempt an answer, a short recap.
aridity index <0.2 = arid
aridity index <0.5 = semi-arid

Values so far:
Kamloops ------------------0.282
Osoyoos---------------------0.308
Penticton-------------------0.339
Lytton-----------------------0.368
Lethbridge------------------0.376

Now for an answer (or at least an attempt).

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 1912-1970 (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 as talked about in the first page of this thread. According this data as shown on the Köppen climate classification map, Ashcroft is a true desert! (Notice the little pink area in BC). Status: arid.

In summary, Ashcroft is indisputably the most arid place in BC, but it is unclear if it can be classified as arid or semi-arid. Depending on how much wind speed, sunshine, and humidity has changed over time, Ashcroft may be semi-arid today even thought it was most definitely arid back in the 20s and 30s when 150mm would be a wet year. Given the fact that Köppen climate classification method classifies Ashcroft as arid, and given the past precipitation data, a balance of probabilities indicate that true desert conditions exist around Ashcroft.

[tsayta]

cool