Saturday, May 27, 2023


Breakup is nearly complete now to the south of the Arctic Circle, but flooding problems continue on the Yukon River.  Heavy inflows from the Porcupine are keeping water levels very high downstream of Fort Yukon, and far to the southwest ice jam flooding has been a problem all week around Russian Mission and more generally in the Yukon delta region.  Flood warnings are now in effect all the way to the coast at Emmonak and Alakanuk.


Following up a bit more on the relationship between Alaska's fire season and the tropical Pacific, here's a map of June-July sea surface temperature patterns for the top 10 fire seasons since 1979 (all over 2 million acres).

This is interesting because it shows a "central Pacific El Niño" signal, and the eastern equatorial Pacific shows no unusual warmth at all.  A classic El Niño SST pattern would be focused in the eastern tropical Pacific: here's the average anomaly in the top 10 summer El Niño events since 1950.


So the Alaska fire equation is not as simple as El Niño = active fire season.  But we already know that, because prior to 1995 there were plenty of El Niño events without notably enhanced Alaskan wildfire.  Here's the average anomaly in those years (June-July El Niño between 1979 and 1995):

The obvious difference here is that both the northwestern and northeastern Pacific were cooler in those years; and of course some of the pre-1995 El Niño events were quite weak.

Now what about last year?  La Niña was entrenched in 2022, with plenty of cool water in both the central and eastern equatorial Pacific, but the North Pacific had much more widespread and unusual warmth than is typical for a strong La Niña.  The second map below shows the average SST anomaly for the top 10 summer La Niña events since 1950.

So if I had to guess, last year's active fire season had a lot to do with the warm North Pacific, especially in the western Bering Sea and south of the Aleutians.  A warm North Pacific is clearly associated with higher fire activity, as in the first SST map above.

As for this year, while we do have El Niño emerging, it's very much focused in the eastern Pacific, with no unusual warmth yet in the central tropical Pacific.  There's also much less warmth in the western Bering Sea than last year; so it seems the pattern is not particularly well aligned with a typical active fire season pattern.  However, SST anomalies can change quickly in summer.  It will be fascinating to see how this season plays out.

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