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Calima: when the Saharan dust actually arrives
Calima is the one Tenerife weather event that can actually spoil a week, and it is the one every guide describes with a shrug. Here is the frequency, the intensity and the duration, by month and by zone.
Pick a zone
| Month | Days over EU PM10 limit | Noticeable dust | Heavy dust | Median PM10 | Worst 10% of days | Days |
|---|---|---|---|---|---|---|
| January | 19% | 26% | 10% | 18 µg/m³ | 120 µg/m³ | 93 |
| February | 20% | 27% | 12% | 18 µg/m³ | 130 µg/m³ | 85 |
| March | 1% | 1% | 0% | 11 µg/m³ | 19 µg/m³ | 93 |
| April | 8% | 10% | 0% | 13 µg/m³ | 37 µg/m³ | 90 |
| May | 0% | 0% | 0% | 11 µg/m³ | 18 µg/m³ | 93 |
| June | 0% | 1% | 0% | 12 µg/m³ | 22 µg/m³ | 90 |
| July | 2% | 2% | 0% | 13 µg/m³ | 27 µg/m³ | 93 |
| August | 12% | 18% | 0% | 17 µg/m³ | 56 µg/m³ | 93 |
| September | 7% | 8% | 1% | 12 µg/m³ | 31 µg/m³ | 90 |
| October | 9% | 14% | 3% | 13 µg/m³ | 38 µg/m³ | 93 |
| November | 14% | 19% | 2% | 13 µg/m³ | 88 µg/m³ | 90 |
| December | 30% | 40% | 11% | 17 µg/m³ | 126 µg/m³ | 93 |
“Noticeable dust” = daily mean Saharan dust over 50 µg/m³; “heavy” = over 200 µg/m³. The PM10 column uses the EU daily limit value of 50 µg/m³, which is a health standard, not a visibility one — a day can cross it and still look merely hazy.
How long an episode lasts
Frequency alone is misleading: what ruins a trip is not a dusty afternoon, it is a dusty week. These are runs of consecutive days above the EU limit.
| Zone | Episodes per year | Typical length | Longest observed |
|---|---|---|---|
| South resorts (Costa Adeje / Los Cristianos) | 12 | 2 days | 18 days |
| North coast (Puerto de la Cruz) | 9.7 | 2 days | 17 days |
| Santa Cruz / La Laguna | 9.7 | 2 days | 17 days |
| Las Canadas / Teide (2.000 m+) | 9.7 | 2 days | 17 days |
What the record says
The result that surprised me is the seasonality. The story you hear repeated is that calima is a summer thing, arriving with the heat. In this record the worst month on the south coast is December, with the EU daily PM10 limit exceeded on30% of days, followed by February at 20%. August is real but it is not the peak.
This is not a contradiction of the summer story so much as two different phenomena wearing the same name. Summer calima tends to ride in high and hot, which is why it is memorable; winter dust arrives in a lower, cooler layer that hangs around the coast. The health metric used here — daily mean PM10 at ground level — picks up the second one more readily than the first.
At the other end, 2 months (May, June) recorded no days at all above the limit in this sample. With only 3 years behind it, read that as “rare”, not “impossible”.
On duration: the south coast sees about 12 episodes a year, the typical one lasting 2 days. But the tail is long — the worst run in the record lasted 18 days. That asymmetry is the practical point: the median episode is a nuisance you can wait out, and the tail is the one that eats a holiday.
The honest limitation
Three years is a thin sample for monthly statistics, and I would rather say so than dress it up. The ranking of months is probably stable; the exact percentages are not. Extending this back to 2003 is possible using the Copernicus CAMS reanalysis directly rather than through a convenience API, and that is the next thing worth doing to this page.