Historic Floods of Earth

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Fig. Flood source records by year

Year

Summary statistics

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Triggers and contributing mechanisms

These mechanisms can act alone or in combination.

Triggers and contributing mechanisms of riverine floods
Mechanism	Contribution
Rainfall	Rainfall-generated runoff.⁹
Snow and ice melt	Snow or glacier-ice melt.¹⁰
Water releases	Releases from reservoirs or natural lakes.^11,12
Blockages	Ice or debris blockages and their sudden release.^13,14
Failures and backwater	Failure of natural or artificial dams or embankments.^15,16 Downstream backwater effects, including high sea levels impeding river discharge.¹⁷
Earthquake effects	Earthquake-induced channel deformation or diversion through surface fault rupture.¹⁸
Reduced conveyance	Sediment accumulation, channel narrowing or structural constrictions that reduce channel capacity.^19,20
Groundwater contribution	Groundwater discharge into rivers, which can contribute to and sustain flooding.²¹

Recorded information

The catalogue records flood locations, with additional observations where available and applicable.²²

Information recorded in the NKUA flood catalogue
Information	Availability
Coordinates	Flood location
Administrative units	Regional unit and municipality
Rainfall duration	Where available and applicable
Rainfall amount	Where available and applicable
Deaths	Where available and applicable

Submit a historic flood event or correct an existing record. Use one row per affected location and event date, with a traceable source and documented impacts.

Prepare your submission

Fill in the blank Data sheet in the XLSX workbook. The Field guide describes every column, its units and examples. You can also use the CSV with the same headers.

Leave unknown values blank. For a correction, include the existing id and explain the change in submission_notes.

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Required fields

Field and column	Format and unit	What to provide
Event start date `date_of_commencement`	YYYY-MM-DD (text)	Documented start date as YYYY-MM-DD text, including dates before 1900. If the exact date is uncertain, explain the documented date in submission_notes.
Country `country`	Text	Country containing the submitted site. Contributions are not limited to the current geographic coverage.
Administrative area or locality `location_name`	Text	Administrative area or locality affected by the flood.
Affected place or event `flood_event_name`	Text	Specific affected settlement, site or recognised event name.
Latitude `latitude`	WGS84 (degrees)	WGS84 decimal latitude. Use a minus sign south of the equator.
Longitude `longitude`	WGS84 (degrees)	WGS84 decimal longitude. Use a minus sign west of Greenwich.
Supporting source `source`	Text	Traceable publication, DOI, report or source URL supporting this record. Include page or figure numbers where relevant.

Optional fields (7)

Field and column	Format and unit	What to provide
Existing record ID `id`	Whole number	For a correction, copy the ID of the existing map record. Leave blank for a new record.
Recorded fatalities `deaths_toll_int`	Whole number	Number of recorded deaths. Blank means unknown. Zero means explicitly none.
Reported cause `cause_of_flood`	Text	Cause of the flood as documented by the source.
Rainfall duration `rainfall_duration`	Text	Reported duration including its unit, such as hours or days.
Rainfall amount `rainfall_height`	Text	Reported precipitation depth including unit and measurement period.
Documented impacts `relevant_information`	Text	Recorded damage, affected infrastructure and other relevant event details.
Submission notes `submission_notes`	Text	Explain corrections, coordinate accuracy, measurement methods, vertical datum and any uncertainty. Identify attachments here.

Site guidance

Enter historic dates as YYYY-MM-DD text so dates before 1900 are preserved in Excel.
Do not invent a day or month when the source gives only a year. Describe an uncertain date in submission_notes so the team can assess it.
A blank death toll means unknown. Enter zero only when the source explicitly records no fatalities.
Keep rainfall duration and rainfall height separate. Retain the reported units, period and any ranges or uncertainty.
Place names may use their normal spelling. Uppercase text is not required.

Include contributor names, affiliation and contact details in your email. Attach the completed file and supporting sources manually. The research team reviews each submission before publication.

What is a flood?

Definition

A flood is the temporary covering by water of land that is normally dry.^1,2

Floodwater covering agricultural fields near Palamas, Thessaly, with trees and hills visible. — Flooded fields near Palamas, Thessaly, September 2023. Photo: Makis Theodorou · CC BY-SA 3.0 (cropped).

How floods are classified

Floods are described using different criteria. A riverine flood can also be a flash flood: one describes its water source, the other its rapid response.^3,4,5

Examples of flood classifications grouped by the criterion used
Criterion	Examples
Water source	Riverine (fluvial), pluvial (surface water), groundwater, coastal (seawater), lake (lakeshore) and artificial water-bearing systems.^3,6,9
Onset and response	Flash, other rapid-onset, medium-onset and slow-onset floods.^3,5
Generating process	Long-rain, short-rain, rain-on-snow and snowmelt floods.⁷
Inundation mechanism	Channel overflow, overtopping of defences, defence or infrastructure failure, and blockage.³
Sediment behaviour	Clear-water floods, debris floods and hyperconcentrated flows.⁸
Setting	Flooding in urban areas, river floodplains, and coastal or estuarine settings.⁶
Interacting drivers	Compound flooding, such as river discharge combined with elevated sea levels or rainfall.⁶

Debris floods are water-driven events with intense coarse-sediment transport. Debris flows are sediment–water mass movements with different flow mechanics.⁸

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