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Environmental information systems
Too much rain falling too fast can trigger floods and landslides. A tenth of Europe’s urban population is currently living in flood-risk zones (EEA, 2020: Healthy environment, healthy lives: how the environment influences health and well-being in Europe). Floods can be deadly and costly, destroying buildings, infrastructure (transport, energy, communication) and livelihoods for all in their path. Between 1980 and 2017, floods have taken some 4,300 lives and cost Europe’s economy more than €170 billion, representing nearly a third of the total damage from natural hazards (EEA, 2020: Economic losses from climate-related extremes in Europe). Whether a heavy precipitation event triggers a dangerous flood is also influenced by non-climatic factors, such as land use, changes to river basins and natural water flow characteristics (dams, changes of river beds, sealing surfaces) and urban planning.
Note: The availability of data for large-scale heavy rain events is better than that for local short-term downpours, which may not be captured by weather stations or represented well in current regional climate models. Therefore, most assessments of extreme precipitation over Europe, including the indices presented here, have used daily data to determine changes in heavy precipitation events.
Maximum consecutive five-day precipitation
Definition
The maximum consecutive five-day precipitation index accounts for the greatest precipitation total over five consecutive days in a year.
Index factsheet (ETC/CCA Technical Paper): Maximum consecutive five-day precipitation
Relevance
The index is relevant for water management, agriculture and disaster risk assessment, in particular for the assessment of river flood, landslide and erosion risks. The simple definition of this index enables it to be easily applied and interpreted.
Past and projected changes
Annual maximum consecutive five-day precipitation has slightly increased since 1950 in northern Europe and possibly in central Europe, whereas no significant change has occurred in southern Europe. Further slight increases in northern and central Europe are projected throughout the 21st century.
Annual maximum five-day precipitation for the European land area and sub-regions
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Extreme precipitation total
Definition
The extreme precipitation total index represents the total precipitation on all days with heavy precipitation, defined as precipitation exceeding the 99th percentile of daily precipitation values over the reference period. Therefore, the index accounts for both the frequency and the magnitude of unusual precipitation events identified with respect to baseline conditions. Variations of this index could use a different percentile (e.g. the 95th percentile) depending on the particular application and the level of rarity of the events to be considered.
Index factsheet (ETC/CCA Technical Paper): Extreme precipitation total
Relevance
The index is mainly relevant for water-related sectors, agriculture, transport and urban-related applications. It provides information on changes in the overall amount of rain falling during intense precipitation events, which can affect the risk of floods, landslides and erosion.
Past and future changes
The extreme precipitation total has increased since the 1950s in Europe as a whole as well as in northern and central Europe. Projections suggest that there will be large increases in northern Europe and somewhat smaller increases in central Europe throughout this century. No significant changes have been observed in or projected for southern Europe.
Extreme precipitation total for the European land area and sub-regions
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Frequency of extreme precipitation
Definition
The frequency of extreme precipitation index refers to the total number of days in a year with total precipitation exceeding the 99th percentile of daily precipitation values during the reference period. Variations of this index could use a different percentile (e.g. the 95th percentile) depending on the particular application and the level of rarity of events to be considered.
Index factsheet (ETC/CCA Technical Paper): Frequency of extreme precipitation
Relevance
This index is relevant for water management, urban planning, transport and agriculture, in particular for assessing risks related to floods, landslides and erosion.
Past and future changes
The frequency of extreme precipitation has increased in Europe as a whole since the 1950s, as well as in northern and central Europe. Projections suggest that there will be large increases in northern Europe and smaller increases in central Europe. No significant changes have been observed in or projected for southern Europe.
Frequency of extreme precipitation for the European land area and sub-regions
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River flood index using runoff
Definition
The river flood index using runoff is defined as the maximum daily river discharge for a given return period (typically 50 or 100 years, depending on the specific application). The index is computed using river flow data, which are derived from hydrological models.
Index factsheet (ETC/CCA Technical Paper): River flood index using runoff
Relevance
The index is relevant for assessing flood risks for transport and other infrastructure, and for urban planning.
Past and projected changes
Trends in rare flood events are difficult to study from observations because of the limited length of available time series and the compound effect of climate change and changes in river management. Based on the European Flood Database, the annual maximum daily river discharge, which is a reasonable proxy for changes in rarer and more extreme floods, was found to increase in north-western Europe and parts of central Europe, but to decrease in southern and north-eastern Europe. A similar geographical pattern was found for floods with a return period of 100 years.
The projections of future changes in maximum 50-year river discharge shown in the figure below are derived from a Copernicus Climate Change Service (CS3) Climate Data Store (CDS) data set based on the outputs of the E-HYPE hydrological model, driven by an ensemble of four bias-adjusted EURO-CORDEX simulations. A fuller uncertainty assessment would require the outcomes from multiple hydrological models to be compared. According to these projections, 50-year river flood levels are projected to increase in most areas in Europe, in particular in central and central-eastern Europe. In some areas, a doubling of discharge levels is possible by the end of the century under the high-emissions scenario (representative concentration pathway (RCP)8.5). Decreasing river flood levels are projected for some regions in southern Europe, especially south of the Iberian Peninsula and in Turkey. However, river floods are projected to increase in many regions in southern Europe even though overall precipitation is projected to fall.
Further information (EEA indicator assessment): River floods
Projected changes in 50-year river flood events in Europe
Notes: The top panel shows the 1971-2000 mean values based on the median of four E-HYPE hydrological simulations. The bottom row shows the ensemble median of the projected relative changes for the near and far future compared with the 1971-2000 reference period. The maps show the gridded values at a resolution of 0.11 ° × 0.11 °. An ensemble median is used to filter out the very local discrepancies among the four simulations. The ensemble median is composed of four model simulations.
Source: C3S CDS data set — Hydrology-related climate impact indicators from 1970 to 2100 derived from bias adjusted European climate projections.