There's a new study in Science detecting increased multiyear droughts from 1980 to 2018. I didn't cover, but did see that their underlying precip data came from a downscaled weather reanalysis. Genuine Q: How much faith would you put in these trends given that origin? (It gave me pause.) - ThreadSky

voosen.me • 42 days ago

There's a new study in Science detecting increased multiyear droughts from 1980 to 2018. I didn't cover, but did see that their underlying precip data came from a downscaled weather reanalysis.

Genuine Q: How much faith would you put in these trends given that origin? (It gave me pause.)

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sarava.net•42 days ago

Reanalysis is not the best source for precip data, but it's often used because it's conveniently available on the same grid as T, winds, etc. Precip is much more sensitive to the weather model used for the reanalysis than other variables like T, winds, even in regions with good data coverage. /

sarava.net•42 days ago

That's because data assimilation, which is at the heart of reanalysis, doesn't really work well for the highly nonlinear and heterogenous precip process.
Other precip-specific datasets are better, but they may be shorter and not well suited to identify trends in data-poor regions.

jamtam.bsky.social•39 days ago

does dryness cause warming or does warming cause dryness

sarava.net•39 days ago

Initial warming is caused by greenhouse gases. That leads to dryness that can amplify the initial warming (positive feedback)

jamtam.bsky.social•39 days ago

that is the fundamental assumption, with everything that follows being a feedback. what if you actively drain 90% of continental wetland, introduce vast unnatural networks of drainage, degrade landscapes with chemical biocides, land clearing, eradication of species, and turn soils upside down.

sarava.net•39 days ago

In climate modeling, we don't assume feedbacks. In fact, assuming anything without a physical basis is considered a bad thing and we try to minimize that. Feedbacks happen when different physical processes interact, sometimes positively, sometimes negatively. They must balance for climate stability

astill73.bsky.social•39 days ago

📌

climateflavors.bsky.social•42 days ago

I agree, but I think the reanalysis data here has actually been bias-corrected with GPCC, which itself is widely used for precipitation trend analysis. But it's true that neither this paper nor the underlying dataset paper comment on precipitation trend quality.

climateflavors.bsky.social•42 days ago

Generally, variability and trends are more consistent in well-observed regions, less so elsewhere (duh), so I think one has to be careful in the tropics, high latitudes, Africa, etc.

Reanalysis are bad for precip extremes (maybe less of an issue for this new study, idk): https://doi.org/10.1088/1748-9326/ab6a22

voosen.me•42 days ago

Thanks Flavio, that's helpful! The challenge of precip in those parts of the world has been lodged in my brain ever since I learned just how drastically weather station coverage (and precip especially) dropped over Africa since the 1980s.

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