Climate data

Weather and climate data underpin many engineering studies: building energy simulations, comfort studies, system sizing, wind analyses, and climate change adaptation.

However, these data do not all answer the same questions. A weather station describes what was observed at a given location; a forecasting model attempts to predict the weather over the next few days; a reanalysis reconstructs the past climate consistently; and a climate projection explores how climate may evolve over several decades.

These approaches complement one another. Depending on the purpose of the study, the aim may be to represent an average climate, reproduce an actual observed year, analyse an extreme event, or construct a plausible future climate.

Weather and climate: two scales of interpretation

Meteorology describes and forecasts the state of the atmosphere over the short term and often at a local scale: tomorrow’s temperature, the passage of a weather front, or the risk of rain over the next few days. Forecast quality depends strongly on our knowledge of the atmosphere’s initial state and decreases as the forecast horizon extends.

Climate, by contrast, is defined by the statistical properties of weather conditions over a long period, generally several decades: averages, variability, seasonality, the frequency of extremes, and changing trends. A climate projection therefore does not forecast the weather on a particular day in 2050; it explores how these distributions may evolve under different assumptions.

The two approaches are closely connected. Weather observations are used to characterise the observed climate, while an event such as a heatwave belongs both to weather through the way it unfolds and to climate through changes in its frequency, intensity, and duration.

Observed climate

How is weather measured? How does weather forecasting work? What are reanalyses such as ERA5? How are these data converted into hourly weather files that simulation software can use?

The From weather to observed climate page covers observations, weather models, reanalyses, and files representing the current climate: Typical Meteorological Years (TMY) and Actual Meteorological Years (AMY). It also provides access to an interactive tool for exploring temperature trends and anomalies .

Future climate

A climate projection is not a forecast of the weather on a specific day in 2050 or 2100. Instead, it describes how the statistical properties of climate may change: average temperatures, frequency of hot days, precipitation, droughts, and extreme events.

The From scenarios to climate projections page introduces climate scenarios, global and regional models, CORDEX, DRIAS, the TRACC, and the construction of future weather files for engineering studies.

Heatwaves

Heatwaves are particularly important in studies of comfort, overheating, and the resilience of buildings and urban spaces.

The Where weather events meet climate trends page explains the different definitions of a heatwave, how to detect one in a weather series, and how to construct a weather file representing a future heatwave.