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station_id string | date date32 | precip_mm float64 | precip_nophen int8 | precip_quality int8 | precip_homog int8 | max1h_mm float64 | max1h_nophen int8 | max1h_quality int8 | max1h_homog int8 | max10m_mm float64 | max10m_nophen int8 | max10m_quality int8 | max10m_homog int8 | pref int8 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
a0375 | 1974-01-01 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-02 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-03 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-04 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-05 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-06 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-07 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-08 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-09 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-10 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-11 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-12 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-13 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-14 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-15 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-16 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-17 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-18 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-19 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-20 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-21 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-22 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-23 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-24 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-25 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-26 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-27 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-28 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-29 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-30 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-01-31 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-01 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-02 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-03 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-04 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-05 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-06 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-07 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-08 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-09 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-10 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-11 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-12 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-13 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-14 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-15 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-16 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-17 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-18 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-19 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-20 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-21 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-22 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-23 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-24 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-25 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-26 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-27 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-02-28 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-01 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-02 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-03 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-04 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-05 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-06 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-07 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-08 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-09 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-10 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-11 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-12 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-13 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-14 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-15 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-16 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-17 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-18 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-19 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-20 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-21 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-22 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-23 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-24 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-25 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-26 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-27 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-28 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-29 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-30 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-03-31 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-01 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-02 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-03 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-04 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-05 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-06 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-07 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-08 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-09 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
a0375 | 1974-04-10 | null | null | 0 | 1 | null | null | 0 | 1 | null | null | 0 | 1 | 45 |
jma-rain-chiba
Rainfall of the 18 stations of the Japan Meteorological Agency (JMA) in Chiba (千葉県, prefecture number 45 of the JMA), 1974-01-01 to 2026-09-30, with the JMA's flags, as Parquet:
- daily: the daily total, the greatest 1 hour amount and the greatest 10 minute amount of each day, 346,788 station-days;
- hourly: the amount of each hour, 8,025,000 station-hours.
It is the Chiba counterpart of jma-rain-tokyo (same source, same columns), and it reaches into 2026 on purpose, see the next section.
Why Chiba, and why up to September 2026
Chiba had heavy rain and flood events in 2026 that this record covers. They are described in their own sources (not repeated here):
- 令和8年8月千葉豪雨: the JMA's report of 2026-09-16, https://www.data.jma.go.jp/stats/data/bosai/report/2026/20260916/20260916.html, and the Japanese Wikipedia article https://ja.wikipedia.org/wiki/令和8年8月千葉豪雨;
- 令和8年台風第25号: https://ja.wikipedia.org/wiki/令和8年台風第25号;
- 北印旛沼の堤防決壊 (a levee failure at 北印旛沼): the press release of Chiba Prefecture, https://www.pref.chiba.lg.jp/kendosei/press/2026/kitainba.html.
For orientation only, the largest values of the stations in this dataset in August and September 2026 (not a statement about any event): 351.0 mm in a day and 115.0 mm in 1 hour at 千葉 (s47682) on 2026-08-13 (the greatest hourly amount of that day is 107.5 mm, ending at 19:00), and daily totals of 300 mm and more at several stations on 2026-09-21, the largest 375.0 mm at 坂畑 (a1241).
October 2026 is not in this version: a test request that ended in October 2026, a month that had not ended, got an error page from the JMA's form, and the same request ended in September was served. October is to be added after the month has ended.
Source
- The JMA's 過去の気象データ・ダウンロード (download of past weather data),
https://www.data.jma.go.jp/risk/obsdl/index.php. The page sends a form to
/risk/obsdl/show/tableand gets a CSV (Shift_JIS);scripts/02_fetch_daily.shandscripts/04_fetch_hourly.shsend the same form. This is not a published API and can change. The requests were made one at a time, 5 seconds apart. - Stations: the station list of the page for prefecture 45 (
/risk/obsdl/top/station,pd=45), kept asraw/2026-10-30/pref=45/stations_45.json. All 18 stations in it (4 weather stations 気象台等 and 14 AMeDAS stations); none has ended. - Daily values (
aggrgPeriod=1): one request per station for 1974-01-01 to 2026-09-30, elements 降水量の合計 (["101",""]), 1時間降水量の最大 (["105","1"]) and 10分間降水量の最大 (["105","10"]). The first fetch (2026-10-30) ended in 2025-12-31; the request was made again to 2026-09-30 on 2026-10-31 and the values of 1974 to 2025 were identical in all 341,874 station-days. The CSVs of the last fetch are kept unchanged inraw/2026-10-30/pref=45/daily/(the folder is named by the first day). - Hourly values (
aggrgPeriod=9, element 降水量["101",""]): one request per station and year, for the years in which the station has daily values (920 requests, listed inhourly_plan_45.tsv; a request of ten years was refused with HTTP 500 in the Tokyo fetch). 1974 to 2025 on 2026-10-30, 2026 (January to September) on 2026-10-31. The CSVs are kept unchanged inraw/2026-10-30/pref=45/hourly/<station>/<year>.csv. - The time of each CSV is in its first line and in
parquet/daily_files.parquetandparquet/hourly_files.parquet. Every raw file has its sha256 inraw/2026-10-30/pref=45/MANIFEST.json.
Files
| File | Rows | What a row is |
|---|---|---|
parquet/daily.parquet |
346,788 | A station and a day (JST) |
parquet/stations.parquet |
18 | A station |
parquet/hourly.parquet |
8,025,000 | A station and an hour (JST) |
parquet/daily_files.parquet |
18 | A CSV of the fetch: station, file, the time the JMA put in it, rows |
parquet/hourly_files.parquet |
920 | The same for the hourly CSVs |
Columns of daily.parquet
station_id (s + 5 digits for a weather station 気象台, a + 4 digits for an AMeDAS station),
date (JST), then for each of precip (daily total), max1h (greatest 1 hour amount) and max10m (greatest
10 minute amount):
| Column | Meaning (from the JMA's help for the CSV) |
|---|---|
<element>_mm |
The value in mm. Null where the CSV is blank |
<element>_nophen |
現象なし情報: 1 no rain, 0 rain. Only weather stations have it; null for AMeDAS |
<element>_quality |
品質情報: 8 normal, 5 quasi-normal (some data missing, within the allowance), 4 insufficient data, 2 doubtful, 1 missing, 0 not observed |
<element>_homog |
均質番号: a change of the number marks a change of the observing environment; values with different numbers are not directly comparable. The JMA numbers them from 1 within each request |
and pref (45). Every station has a row for every day of the request, also before it started; those rows
have no value. The hourly table has the hours of the years requested for each station only.
stations.parquet has station_id, station_name, pref, kind (synop or amedas), lat and lon
(decimal degrees, converted from the degrees and minutes to 0.1 minute of the list), elevation_m, ended
(the date the list gives for the end of observation; null for all 18) and kansoku (the list's code of the
elements a station observes; 100000 is rain only).
Columns of hourly.parquet
station_id, time_end (the end of the hour, JST, as the JMA writes it: 2026-08-13 20:00 is the hour
from 19:00 to 20:00, and 2026-08-14 00:00 is the last hour of 2026-08-13), then precip_mm,
precip_nophen and precip_quality as above, precip_homog_in_file (the homogeneity number of the CSV of
that station and year; as the JMA numbers from 1 in each request, it can be compared only within a year, use
the daily precip_homog across years) and pref.
The day of an hour is the date of time_end - 1 hour. With that, the 24 hours of a day add up to the
daily total of daily.parquet on 323,828 of the 323,829 days that have 24 hourly values and a daily value;
the other day is at 勝浦 (s47674) and differs by 0.5 mm. The daily greatest 1 hour amount is larger than the
greatest hourly amount of the same day on many days (39,076; it is measured over any 60 minutes, not only
from the hour; this reading is not confirmed by the JMA's text), and smaller on 7 days.
What was changed
- The CSVs were read with their own header rows (weather stations have four columns per element, AMeDAS
three, without 現象なし情報), values made numbers and blanks null. Nothing was dropped, filled or
corrected.
scripts/05_build.pycounts that every CSV row is in the Parquet and that (station, date) and (station, time_end) are unique. In the hourly table only the homogeneity column was renamed. - The Parquet was checked against the CSVs with a second reader (DuckDB's CSV reader,
scripts/06_verify.py): rows, non-null values and sums agree for every station, daily and hourly, with no duplicate keys. Every station and year of the hourly table has 8,760 hours (8,784 in a leap year), and 6,552 hours in 2026 (273 days, January to September). - The Parquet files of the pipeline are partitioned by prefecture (
pref=45) for a later multi-prefecture dataset; here they are placed as single files.
Known issues (measured 2026-10-31)
- AMeDAS stations start in 1976 (船橋, 牛久 and 坂畑 in 1978); the weather stations 銚子, 館山, 勝浦 and 千葉 have values from 1974. The 10 minute maximum of the AMeDAS stations starts in 2008 or 2009 (千葉, 銚子, 館山 and 勝浦: 1974).
- 成田 (a0378) has no daily values from 1978 to 2002 (9,122 days in the span of its record, the rest of the stations have at most 285 missing days).
- A 0 of a weather station is either no rain (
nophen1, 35,164 days) or rain that came to 0.0 mm (nophen0, 15,679 days). An AMeDAS 0 cannot be told apart. - Four stations change the homogeneity number once: 香取 (1999-10-12), 我孫子 (2010-03-11), 木更津 (2006-09-22) and 船橋 (1999-08-03). The station list gives the present positions only.
- In the hourly table 241,954 values are null, and 9,893 station-days have 24 hourly values while the daily total is null; no day has 1 to 23 hourly values.
- The JMA can correct past values. A later fetch of the same request is not guaranteed to return the same CSV (1974 to 2025 did not change between 2026-10-30 and 2026-10-31).
Licence
The JMA's terms for the content of its web site (気象庁ホームページについて, コンテンツの利用について, https://www.jma.go.jp/jma/kishou/info/coment.html) follow the 公共データ利用規約 (第1.0版) (Public Data License 1.0), which is compatible with CC BY 4.0. This dataset is offered under CC BY 4.0, with the credit to the JMA and the statement that it was processed:
出典：気象庁ホームページ「過去の気象データ・ダウンロード」（https://www.data.jma.go.jp/risk/obsdl/index.php）を加工して作成
It is not an official product of the JMA. The terms pages as read are kept in raw/2026-10-30/evidence/.
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