RESIN State of the Art Report (3)
Weather and Climate Hazards Facing European Cities
J. Carter, J. Handley & A. Connelly
This report presents data and insights on European weather and climate hazards that have the potential to impact on cities and urban areas. Developing an understanding of current and potential future weather and climate hazards is an important element of adapting and building resilience to the changing climate. The European Environment Agency defines a hazard as:
'…potentially damaging physical event, phenomenon or human activity characterised by its location, intensity, frequency and probability.' (EEA 2012: 47)
The report concentrates on observations and future projections relating to four key hazards types, sea level rise, flooding, high temperatures and water scarcity and drought, and the temperature and precipitation variables that underpin them. The focus is at the scale of Europe and its sub-regions, with finer scale spatial data presented where this is available. The report does not address impacts of hazards; the focus is on the hazards themeselves. The report aims to enhance understanding of related issues and identify hazard data sources to support building the resilience of cities to climate change. Brief summaries of the key issues relating to the four hazards covered in this report are detailed below.
Sea level rise
- Observations confirm that sea levels have risen by around 20cm since 1900.
- The rate of sea level rise has accelerated over recent decades.
- Projections point towards further sea level rise, at a rate above that experienced over the last century.
- Optimistic projections indicate around 50cm of additional sea level rise by 2100, with levels continuing to increase for several centuries thereafter.
- Higher emissions scenarios, and associated ice sheet melting, could lead to sea levels increasing by over 1 metre by the end of this century.
- Sea level rise increases the risk of coastal flooding, particularly when associated with storm surges and high tides.
- There are several main types of flooding that affect Europe, including flooding from rivers and streams (fluvial flooding), surface water flooding (pluvial flooding), groundwater flooding and snowmelt flooding. This report focuses principally on fluvial and pluvial floods, which are underpinned by sustained and/or intense rainfall events.
- Pluvial flooding is becoming increasingly prominent in European urban areas, although comprehensive modelling and mapping work is as yet limited.
- Climate projections suggest significant change in the pattern of rainfall across Europe, with implications for flooding. Most future scenarios anticipate an increase in rainfall in the north and west, particularly during the winter months. Across the continent, even in southern Europe where rainfall volumes are declining, extreme downpours are projected to become more common.
- Forecasting changes to future flood hazards is complex, particularly at finer spatial scales.
- Despite this, there is some agreement between climate models that certain locations, particularly north western Europe during the winter months, will see an increase in fluvial flood hazard frequency. In other regions, for example around the Baltic sea, central Spain and parts of northern Europe where snowmelt flooding is projected to decline, reductions in fluvial flood hazard frequency are anticipated.
- The frequency and intensity of warm spells and heatwaves has increased over recent decades in Europe.
- The occurrence of warm spells and extreme heatwaves is projected to increase across all European sub-regions.
- Southern Europe and the Mediterranean are most likely to experience a significant increase in the frequency and intensity of heatwaves.
Drought and water scarcity
- Droughts and water stress events already affect many areas of Europe.
- There is a high level of agreement across climate scenarios and models that drought severity will increase over many areas, particularly southern Europe.
- Due to projected rainfall increase, droughts resulting from changes in precipitation patterns are anticipated to become less frequent in parts of northern Europe.
- Although there is a clear north-south split concerning water scarcity and drought projections, climate change is nevertheless projected to increase water stress in many of Europe’s river basins.
- Drought and water stress have a strong socio-economic component, which can exacerbate or moderate their frequency and severity.
In addition to presenting data and insights on weather and climate hazards, this report also highlights several overarching themes relating to hazard events and data.
- Hazard events result from the interaction between weather and climate and the geographical features and socio-economic characteristics of the receiving location.
- Projections on the future frequency and intensity of weather and climate hazards depend on the greenhouse gas emissions scenario selected. However, because it is not possible to determine emissions trajectories, it is also not clear as to the precise nature of future weather and climate hazards.
- Different climate models produce different climate variable and hazard projections, even when using the same underlying emissions scenario.
- The threat of more extreme events is a consistent theme within future climate studies. This is an important issue for Europe given the negative impact that extreme events have on urban areas.
- Uncertainties relating to future hazard projections need to be acknowledged. Nevertheless, there is sufficient data available to make an informed judgement of potential future weather and climate hazards facing European cities and urban areas in order to support adaptation planning and resilience building strategies.