Warm Tibetan Plateau winters account for 56% of California's January 2017 rain anomaly in models
A UCLA-led team reports in Science Advances that heat over the Tibetan Plateau preceded two record California winters. The model attribution is 56 and 30 per cent of the rainfall anomaly, from two cases.
The Scientist · Science desk
What happened
- A Science Advances paper published on 9 September, with UCLA atmospheric scientist Yongkang Xue as first author, identifies the first known climate teleconnection running from the Tibetan Plateau to California.
- The plateau ran unusually warm in December 2016 and February 2023, and roughly a month after each hotspot, parts of California, Nevada, Oregon, Utah and Arizona recorded record-breaking precipitation.
- The paper's modelling attributes 56 per cent of the January 2017 California rainfall anomaly and 30 per cent of the March 2023 anomaly to that plateau heat.
- Both wet spells fell in La Nina winters, when California and its neighbours are usually expected to run dry, which is what made the events puzzling.
- Xue says state-of-the-art forecast systems, which lean heavily on ocean conditions such as El Nino, did not predict either event.
Why it matters
- What's now possible capability The month between plateau warming and West Coast rain sits in the subseasonal range that ocean signals currently serve poorly, so a land-surface temperature that can simply be monitored would be a genuinely new input if the relationship holds up.
- What it limits constraint At 56 and 30 per cent, the plateau is an additional term in a western US precipitation forecast rather than a replacement for ENSO, and any operational use has to carry the ocean predictors alongside it.
- What doesn't add up contradiction Xue's team treats the model agreement as grounds for building the plateau into early warning, while Arun Kumar, formerly of NOAA, says the link needs confirming on fresh data before it is useful for forecasting at all.
- What it sets up precedent If the signal really only appears after 1980 because mountain regions are warming fast, then other high plateaus become candidate predictors, and the same search will be run on records that are similarly short.
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Those two percentages come out of experiments in which the observed plateau warmth is the input, not the unknown. According to New Scientist, the team simulated the effect of record December 2016 warmth over the plateau on the wet weather that arrived in California in January 2017, then repeated the exercise for February 2023 and March 2023 [12]. That design isolates a mechanism rather than testing prediction, since an operational system would first have to forecast the plateau anomaly, then propagate it across the Pacific without smearing it. Live Science reports the models replicated the extreme weather with surprising accuracy [20]. Reproducing an event whose driver you have already specified is the easier half of the job.
Subtract and the accounting is more modest than the link itself: 44 per cent of the January 2017 anomaly and 70 per cent of the March 2023 anomaly are left to everything else [22]. The two shares differ by 26 percentage points, close to a factor of two, across the only two cases in the paper [23]. With two events there is no basis for saying which is the representative one.
The physics is the sturdiest part. As the plateau, which averages more than 4,500 metres above sea level, warmed, a strong gradient formed against the regions north and south of it, generating a disturbance that travelled east along the jet stream as a Rossby wave train toward the Rockies [18][10]. Over the eastern Pacific the wave broke, which Xue says reduced static stability and sharply intensified atmospheric rivers, the narrow corridors of water vapour transport that drive much of the flooding in the western United States [11][14]. Matthew Huber of Purdue, who was not involved, called the analysis a very specific and impactful case study and said it builds on the established idea that extra heat on a mountaintop affects Rossby waves almost as if the mountain had suddenly grown [17].
The false alarm rate is missing from this record. Neither published account describes the converse test: early winters when the plateau ran hot and California's rainfall stayed unremarkable. Xue notes the connection appears in the observational record only after 1980, which he attributes to rapid warming in mountain regions [24]; that also caps how many analogue winters exist to score a predictor against. Andries-Jan de Vries of the University of Lausanne told New Scientist the study nicely demonstrates the effect but that the exact causal mechanisms need further study [15]. Arun Kumar, formerly of NOAA, called the findings intriguing and said more work with fresh data is needed before they can prove useful for forecasting [16].
The test that would settle it is unglamorous: add plateau temperature as a predictor to a subseasonal hindcast over the post-1980 record and score it against the ocean-only baseline, counting misses and false alarms. Until that exists, this is a well-argued mechanism with two cases behind it, and roughly $6.6 billion in damage and at least nine deaths across those two winters [6] is a fair reason to spend the compute on the harder experiment.
What to watch
- A third case: an early winter with anomalous plateau heat, and whether West Coast precipitation follows or does not.
- Whether any forecast centre adds plateau surface temperature to a subseasonal hindcast set and publishes skill scores against an ocean-only baseline.
- Whether the same post-1980 emergence turns up for other high-elevation regions, which would move this from one case study toward a general predictor.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence55
- Adoption
- Not scored
- Hype gap+30
- Incentives
- Not scored
- Confidence60
Perspective Coverage
3 publishers- Builder
- Builder 47%
- Operator
- Operator 41%
- Investor
- Investor 12%
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
The findings were published on Wednesday, September 9, in the journal Science Advances, based on modelling and analyses of precipitation and surface temperature data among other observations.
- [2]
The study is the first time researchers have identified this link between Tibetan Plateau temperatures and California rainfall, a climate teleconnection.
- [3]
The study's first author is Yongkang Xue, a distinguished professor of atmospheric and oceanic sciences at UCLA.
- [4]
In December 2016 and February 2023, the Tibetan Plateau was warmer than usual for those times of year.
- [5]
Roughly one month after each plateau hotspot appeared, parts of California, Nevada, Oregon, Utah and Arizona received record-breaking precipitation.
- [6]
The two events caused a total of around $6.6 billion in damage according to the study, and killed at least nine people.
- [7]
Xue said state-of-the-art forecast systems, which rely heavily on ocean conditions like El Nino, failed to predict this extreme rainfall.
- [8]
The record precipitation occurred during La Nina years, which are typically associated with dry conditions in California and neighbouring regions.
- [9]
In 2017 California experienced its wettest winter on record; January rain that year inundated hundreds of homes, blocked roads and caused power blackouts for more than half a million people.
- [10]
As temperatures rose over the plateau, a strong gradient formed with the regions north and south of it, generating an atmospheric disturbance that propagated eastward along the jet stream via Rossby waves, triggering a Rossby wave train between the Tibetan Plateau and the Rocky Mountains.
- [11]
Xue said that over the eastern Pacific the wave breaks, and this wave-breaking mechanism reduces static stability and significantly intensifies atmospheric rivers, driving extraordinary heavy precipitation along the West Coast.
- [12]
The team used climate models to simulate the effect of record warm weather over the Tibetan Plateau in December 2016 and the wet weather that arrived in California in January 2017, and repeated the modelling for February 2023 over the plateau and March 2023 in California.
- [13]
The results are part of a new body of research examining the influence of land temperatures on weather patterns, and Xue said this is the first study of a winter season in that line of work.
- [14]
Atmospheric rivers are narrow, elongated corridors of intense water vapour transport and are key drivers of precipitation and floods in the western United States.
- [15]
Andries-Jan de Vries of the University of Lausanne said the study seems to nicely demonstrate how anomalous surface heating over the Tibetan Plateau in early winter can affect winter hydroclimate and its extremes across the US south-west coast, but that the exact causal mechanisms linking the plateau to California require further study.
- [16]
Arun Kumar, formerly of the US National Oceanic and Atmospheric Administration, said that while the findings are intriguing, more work is needed to confirm the connection using fresh data before it can prove useful for forecasting.
- [17]
Matthew Huber, a professor at Purdue University who was not involved in the research, called the analysis a very specific and impactful case study and said the results build on the well-established idea that extra heat on a mountaintop affects Rossby waves almost as if the mountain had suddenly grown.
- [18]
The Tibetan Plateau has an average elevation greater than 4,500 metres above sea level.
- [19]
Xue says weather in high-elevation regions such as the Tibetan Plateau can have an effect on weather comparable to sea-surface temperatures.
- [20]
The models replicated the extreme weather with surprising accuracy, raising hopes that the Tibetan Plateau could be integrated into early warning systems.
- [21]
According to the paper, the modelling suggests heat over the Tibetan Plateau can explain 56 per cent of the extreme rainfall anomaly over California in January 2017 and 30 per cent of the rainfall anomaly in March 2023.
- [22]
The attribution leaves 44 per cent of the January 2017 California rainfall anomaly and 70 per cent of the March 2023 anomaly to causes other than Tibetan Plateau heat.
- [23]
The two attributed shares differ by 26 percentage points, a ratio of about 1.9, across the two cases examined.
- [24]
Xue says the connection between the high mountains and California emerges in the data only after 1980, a sign that rapidly rising temperatures in mountainous regions are causing unexpected effects, and says it is certainly something related to climate change.
Sources
3 independent publishers whose own reporting we read for this story.
- livescience.comRecord-breaking rain in California was caused by abnormally high temperatures on the other side of the world, study finds
1 article · September 9, 2026
- newscientist.comHeat spikes over Tibet may help explain severe Californian flooding
1 article · September 9, 2026
- phys.orgHow atmospheric events at the top of the world could have triggered two devastating California floods
1 article · September 10, 2026
Topics and entities
Topics
- Extreme precipitation
- Seasonal Weather Forecasting
- Atmospheric rivers
- Climate teleconnections
Entities
- University of California, Los Angeles
- Andries-Jan de Vries
- NOAA
- Science Advances