Artificial Wasteland · phenology & the long record

A Thousand Springsthe Kyoto cherry has been watched for twelve centuries — and it has never bloomed as early as now

In the spring of 812, a scribe in the imperial court of Kyoto noted the day the cherry came to full bloom. People never really stopped. Across 1,200 years — through diaries, chronicles, temple registers, and finally newspapers — 838 of those dates survive. Plotted together they hold almost flat for a millennium. Then, at the very last, they fall off a cliff. The two earliest full blooms in the entire record are 2023 and 2021; you have to go back to 1409 to find the next.

This is one of the longest phenological records on Earth — a single, ordinary springtime event, watched by an unbroken chain of observers who mostly never knew they were building anything. The dates below are theirs. Everything here is drawn from the record that phenologist Yasuyuki Aono assembled from the primary sources; nothing is modelled or smoothed away. Where the record is uncertain, this page says so.

INSTRUMENT · ONEThe whole record, at a glance

Each mark is one recorded spring: how far into the year the Kyoto cherry reached full bloom. Higher is earlier. Drag across it — or use the slider below — to read any single year.

Hollow marks are the 14 dates Aono estimated from a related record; solid marks are direct observations. The amber dashes are the pre-1900 average (April 15). The pink curve is a 30-year moving average.

INSTRUMENT · TWORead a single spring

Move the slider through the 838 recorded years. Each card is a real entry: the date the cherry was seen in full bloom, and the source that wrote it down.

Year
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Full bloom
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Day of year
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Recorded in
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INSTRUMENT · THREEThe ten earliest springs ever recorded

Rank all 838 springs by earliness. Pink years are the modern edge. Eight of the earliest thirty springs in twelve centuries have fallen since the year 2000.

    What warms the cherry

    A cherry tree in Kyoto opens when late winter and early spring have been warm enough — the buds integrate the temperature of roughly February and March. Aono used exactly this to run the record backwards: because full-bloom date tracks March temperature closely, the twelve centuries of dates become a thermometer, letting him reconstruct Kyoto's early-spring temperatures back to the 9th century to within about a degree. The recent run of early blooms corresponds to the warmest late winters in the reconstruction.

    The honest caveats — what this record can and can't say

    A city is a warm thing. Modern Kyoto is a large urban area, and cities hold heat. Part of the recent earliness is this local urban warming, not the wider climate. Aono's temperature work explicitly separates the two — estimating and subtracting the urban-heat-island effect — and finds a warming signal that remains after the city is accounted for. The raw bloom dates on this page cannot make that separation by themselves; they show the trend, not its full attribution.

    Not every year, and not all the same. The record has gaps — many years have no surviving note — and 14 of the 838 dates are Aono's estimates from a first-flowering or related mention rather than a direct full-bloom record (they are marked, and all fall before 1600, so none touch the modern record). Observers and even the trees changed over centuries; Aono standardised to a consistent full-flowering criterion, but the deep past is read through documents, with the care that demands.

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