The West’s Torrential Rains, Drought, and La Nina

October 25, 2021

As a torrential “atmospheric river” drowns the west, breaking, for the moment, a historic drought, it’s worth remembering that the emergent pattern of precipitation coming more often in giant dumps is not ideal to get out of a dry spell.

Cloudbursts and gullywashers tend to run off quickly, as opposed to the more frequent, slow, soaking rainfall that actually feeds soil and aquifers in a sustainable way.
I put the question to Kevin Trenberth a few years ago and got a lucid explanation, above.
Below, Daniel Swain updates on the California situation.

Below, more perspective from my recent chat with Park Williams of UCLA.
He points out, importantly, that rising temperature means more precipitation will fall as rain rather than snow at high altitudes, affecting the snow storage capacity of mountain reservoirs, and snow melts off sooner in the spring, leaving a longer period for unprotected soil to dry out.

Below, Williams notes that the mega droughts of the past have coincided with La Nina-like configurations in the Pacific. He notes, (and Trenberth mentions above) that recent dry decades in the west have coincided with the generally “La Nina” like pattern that seems increasingly stuck. Not that there are no El Ninos, but they are fewer and farther between.

2 Responses to “The West’s Torrential Rains, Drought, and La Nina”

  1. rhymeswithgoalie Says:

    Cloudbursts and gullywashers tend to run off quickly, as opposed to the more frequent, slow, soaking rainfall that actually feeds soil and aquifers in a sustainable way.

    I saw a video years back (possibly here) about one hydro activists who went to farming areas in the mountainous areas of India where the change in monsoon rains and glacier melt meant that they didn’t have enough water at the end of the season. He showed them a way to retain more of the wet-season water in their local aquifers by use of sustainable excavation technology (shovels). They dug channels and pits that redirected and captured high water, holding it long enough to recharge their water tables and aquifers rather than letting it all flow by.


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