{"id":"uk-historical-rainfall","slug":"uk-historical-rainfall","name":"UK Historical Rainfall Dataset","description":"Monthly, seasonal and annual rainfall for the United Kingdom, its four nations and the twelve Met Office climate districts, running from 1836 to the present. One of the longest continuous instrumental rainfall records available anywhere under an open licence.","methodology":"Collected directly from the Met Office HadUK-Grid areal series, which are computed by the Met Office from the national rain-gauge network interpolated to a 1 km grid and then averaged over each area. Hydrionis parses the published fixed-width series by reading column positions from the header row, so a change in the publisher’s layout fails loudly rather than shifting values between months. Values are stored at the area they were reported for and are never redistributed to administrative units the Met Office did not report.","domains":["precipitation"],"metricIds":["precipitation-annual","precipitation-monthly","precipitation-seasonal"],"subjectScope":"United Kingdom, four nations, twelve Met Office climate districts","cadence":"monthly","version":"1.0.0","released":"2026-08-24","changelog":[{"version":"1.0.0","date":"2026-08-24","summary":"First release. Replaces the hand-transcribed rainfall normals carried before automated collection.","corrections":["Reference normals are now computed from the full 1991–2020 series rather than transcribed. The computed England normal is 870 mm against the previously published 838 mm — a 3.8% correction."],"additions":["Full monthly, seasonal and annual series from 1836 for 17 areas.","Twelve Met Office climate districts added as first-class geographies."]}],"limitations":["Areal averages, not point measurements. No value here describes rainfall at a specific location.","Gauge density varies over the record, and mountain precipitation is systematically under-measured by rain gauges. Early decades rest on a sparser network than recent ones.","Climate districts are Met Office reporting areas and do not align with administrative or river-basin boundaries."],"context":{"hydrionisClass":"water-driver","whyHeld":"Rainfall is not water in a river, and almost every question about a British river begins with it. This is the longest openly licensed instrumental rainfall record Hydrionis holds — 1836 to the present for the UK and its nations — and it is here to explain flow, recharge and drought rather than to measure them.","waterRelevance":["River flow across the UK","Groundwater recharge in the chalk and limestone aquifers","Reservoir inflow and drawdown","The historical droughts the UK water industry plans against, 1976 among them"],"suitableUses":["Placing a wet or dry period in its full instrumental context for a nation or Met Office district","Showing rainfall beside flow, level or storage on a shared time axis","Long-run trend and variability analysis at the areas the Met Office actually reports"],"unsuitableUses":["Any statement about rainfall at a point. These are areal means: a district mean can be dry while part of the district floods","Attributing a specific flood or drought at a specific gauge to these figures without that catchment’s own record","Comparison with station daily totals as though they were the same measurement"],"joinDimensions":[{"kind":"same-administrative-geography","on":"The UK, its four nations and the twelve Met Office climate districts, which Hydrionis also holds as geographies","limitation":"A district contains many catchments and a catchment may cross districts. Sharing a district with a gauge is not sharing its hydrology."},{"kind":"time-only","on":"Shared monthly, seasonal and annual periods with any other Hydrionis series","limitation":"A shared time axis supports showing two series together and establishes nothing about either."}],"relationshipConfidence":"documented","eligibility":{"api":true,"download":true,"overlay":true,"publicPage":true}},"observationCount":173673,"seriesCount":409,"subjectCount":375,"from":1836,"to":2026,"sourceIds":["uk-metoffice-haduk","uk-sepa"],"units":["mm"],"redistributable":true,"commerciallyReusable":true,"citation":"Hydrionis (2026), UK Historical Rainfall Dataset, version 1.0.0. Retrieved from https://hydrionis.com/data/datasets/uk-historical-rainfall/","downloads":[{"file":"/downloads/observations-precipitation-uk-sepa.csv","format":"CSV","label":"precipitation observations from SEPA (118,942 rows)"},{"file":"/downloads/observations-precipitation-uk-metoffice-haduk.csv","format":"CSV","label":"precipitation observations from Met Office (55,420 rows)"}],"apiPath":"/api/v1/datasets/uk-historical-rainfall.json","lastFetched":"2026-10-05","fields":[{"id":"precipitation-annual","name":"Annual precipitation","definition":"Total depth of precipitation falling over a defined area in a calendar or water year.","unit":"mm","nativeGeography":["monitoring-station","grid-cell"],"comparabilityNotes":"Annual totals for different countries are not comparable as a measure of water availability. A large arid country and a small wet one can have similar national average rainfall while having entirely different renewable water resources per person. Gauge networks also differ in density, and mountain precipitation is systematically under-measured."},{"id":"precipitation-monthly","name":"Monthly precipitation","definition":"Total depth of precipitation falling over a defined area within a calendar month.","unit":"mm","nativeGeography":["monitoring-station","grid-cell"],"comparabilityNotes":"Monthly totals are dominated by seasonality. Compare a month against the same month in other years, or against the long-term average for that month, never against an adjacent month."},{"id":"precipitation-seasonal","name":"Seasonal precipitation","definition":"Total depth of precipitation falling over a defined area within a meteorological season.","unit":"mm","nativeGeography":["monitoring-station","grid-cell"],"comparabilityNotes":"Meteorological seasons are fixed three-month blocks — winter is December to February, and its December belongs to the previous calendar year. Comparing a season across years is valid; comparing adjacent seasons is not."}]}