This city report was originally published with errors in the data. An algorithm meant to reconciliate two ECMWF datasets to make them comparable was never applied for this city, and its temperature increase was therefore exaggarated. The affected numbers have now been corrected. For an in-depth explaination of this incident, see:

Temperature trends since 1900 in and around Beja

Using data from the European Centre for Medium-Range Weather Forecasts, we analysed 118 years of weather data in and around the city of Beja. The area analysed also includes the surroundings of Beja, which might include mountains or bodies of water, so that the temperatures shown here do not correspond exactly to the temperatures recorded by the weather stations of Beja (see Methodology for details). This is what we found:

  • The temperature in and around Beja between 2000 and 2018 was 0.8°C above the 20th century average.
  • The number of hot days (above 28°C over a 24-hour average) went from 5.5 days per year in the 20th century to 13.1 per year in the years since 2000.

Changes in weather patterns

Temperature changes

Since 1900, the average temperature in and around Beja increased from an average of 16.6°C between 1900 and 1999 to an average of 17.4°C between 2000 and 2018. The warmest years in and around Beja were 2017, 1995, 1949, 2015, and 2009.

Temperature in and around Beja from 1900 to 2018. (png|svg|eps)

Hot days

In the 20th century, the average number of hot days (days for which the 24-hour average temperature is above 28°C) per year was 5.5. Between 2000 and 2018, the average number of hot days were 13.1 per year.

A day is considered hot when its average temperature is over two standard deviations of the normal average.

Number of days when the average temperature was above 28°C in and around Beja, each year. (png|svg|eps)

What does it mean for Beja?

Health and heat waves

Higher temperatures lead to excess mortality. The heatwave of July and August 2003, for instance, killed over 52,000 people in Europe, according to the Earth Policy Institute (Larsen, 2006), a think-tank. The elderly and infants are most at risk.

Rising temperatures may also cause the number of deaths related to extremely cold weather to drop.

Rail buckling and tarmac softening

In high temperatures, asphalt exposed to the sun starts to soften. This causes delays and some roads have to be closed to traffic.

When temperatures rise above 30°C, rails exposed to the sun can move or buckle. This can cause trains to derail, as happened many times in Europe already, and forces them to run more slowly, causing major delays.

Tick and mosquito-borne diseases

Tick-borne encephalitis, and more recently ehrlichiosis have been spreading in the past decades, probably due to higher temperatures (Gray et al., 2009).

Dengue fever, carried by the Aedes aegypti and Aedes albopictus mosquitoes, has been creeping North in the last decade, with epidemics in Portugal in 2012 and Japan in 2014 (Zeller et al., 2013). The Mediteranean basin is most at risk.


Researchers showed that when the daily average temperature increases above 22°C (Graff Zivin et al., 2018), cognitive abilities of school children decrease, especially in mathematics.

In Beja, the number of school days above 22°C went from 12.9 per school year in the 20th century to 22.1 since 2000. It might not seem much but if exams took place on these days, pupils of Beja were at a disadvantage.

Beja and its environs in context

Beja and nearby cities

Here are the five locations closest to Beja, among the 558 we analyzed:

LocationDistanceTemperature change
Évora61 km+0.8
Setúbal105 km+0.5
Faro107 km+0.7
Huelva116 km+0.8
Badajoz122 km+0.9

Cities of Portugal

Beja is one of twelve locations in Portugal we have analyzed. This is how temperature has changed in the rest of them.

LocationTemperature change
Vila Nova de Gaia+0.4
Ponta Delgada+0.1
Cities of Portugal
Cities of Portugal(png|svg|webp)


We analyzed two data sets from the European Centre for Medium-Range Weather Forecasts (ECMWF), ERA-20C for the period 1900–1979 and ERA-interim for the period 1979–2018.

Both data sets are re-analysis, which means that ECMWF scientists used observations from a variety of sources (satellite, weather stations, buoys, weather balloons) to estimate a series of variables for squares of about 80 kilometers in side width (125 kilometers for ERA-20C). While weather stations offer a much better record for immediate daily observations, using the ECMWF re-analyses is much more adequate for the study of long-term trends. Weather stations might move, or the city might expand around them, making their data unreliable when looking at centennial trends. However, the ECMWF data does not take into account micro-climates or “heat island” effects, so that the actual weather in the streets of Beja was probably one or two degrees warmer than the values reported here (the trend, however, is the same).

Since the start of this project, ECMWF has adjusted the way historical temperatures are calculated, to give better estimates for e.g. coastal cities. Because of this, some figures published here in 2019 may differ slightly from corresponding figures published in 2018.

This report was produced by the European Data Journalism Network. Partners include OBC Transeuropa (Italy), J++ (Sweden), Spiegel Online (Germany), Vox Europe (France), Pod Crto (Slovenia), Mobile Reporter (Belgium), Rue89 (France), Alternatives Economiques (France), and El Confidencial (Spain).


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Graff Zivin, Joshua, Solomon M. Hsiang, and Matthew Neidell. "Temperature and Human Capital in the Short and Long Run." Journal of the Association of Environmental and Resource Economists 5.1 (2018): 77-105.

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