Climate change is responsible for affecting outdoor activities with increasingly frequent adverse weather conditions. In Catalonia, because of the heat, the summer is the most challenging time of year for organising outdoor activities. Human tower building is an example of this, as the principal days on which it occurs coincide with important festivals in June, July, August and September - although events can now also be seen right through from February to November.
Given that rises in temperature attributed to human-induced climate change will increase the likelihood of adverse weather such as heatwaves coinciding with human tower building events, a research team from the URV's Department of Geography at URV has studied the challenges facing the tradition. The project has been carried out within the framework of the URV Chair for the Study of the Human Tower Building.
In fact, historical meteorological data confirm this trend: between 1951 and 2023 temperatures rose between 0.3 and 0.4 degrees per decade on dates when human tower building events are traditionally held, for example St John's Day (24 June) in Valls, St Magin (19 August) in Tarragona, St Felix (30 August) in Vilafranca del Penedès, or the main festival of La Bisbal del Penedès (15 August). These data confirm that there has been a sustained, statistically significant deterioration in the weather conditions for human tower building in the summer. Heat indices-a measure that combines temperature and humidity-for the same period show a very similar pattern: there are fewer and fewer days with a neutral heat index (below 26°) and a growing number of days marked with "caution" (above 26°) and "extreme caution" (above 32°C).
Evolution of average temperature 12-15h (left) and temperature anomalies (right): Valls - 24/6 (a); La Bisbal del Penedès - 15/8 (b); Tarragona - 19/8 (c) and Vilafranca del Penedès - 30/8 (d)
Heat Index values 1951-2023
In 2024, temperature and humidity sensors were installed in public squares where human tower building takes place with the aim of collecting first-hand meteorological data. On the basis of this, a climatic database was generated for the human tower building events held at midday, namely St John's in Valls (24 June), the festival of Banyeres del Penedès (14 July), St Anne's in El Vendrell (26 July), St Magin in Tarragona (19 August), the festival of l'Arboç (25 August), St Felix in Vilafranca del Penedès (30 August) and St Rosalia in Torredembarra (1 September), other events held in the afternoon such as the Day of Cultures in Altafulla (13 July), the festival of Llorenç del Penedès (11 August) and the festival of La Bisbal del Penedès (15 August) and, one that is held in the evening, this being Firagost in Valls (7 August).
Analysis of the data has revealed that the temperature exceeded 30 degrees on seven of the eleven days analysed. The highest temperatures recorded were 34.6° in the Plaça de la Vila in Vilafranca del Penedès on 30 August; 34.4° in the Plaça de la Vila in Torredembarra on 1 September; and 33.9° in the Plaça Vella in El Vendrell on 26 July. As expected, the temperature in the square is higher in direct sunlight than in the shade, with up to a 4°C difference recorded on the day of St Felix in Vilafranca.
In most cases, the temperature is higher in the squares than at other points in the nearby rural environment. Although small deviations in these readings can be explained by the use of different sensors or the distance between the square and the nearest weather station, the main reason is a phenomenon called the "urban heat island". Basically, the construction materials used in cities and the absence of vegetation cause heat to accumulate on surfaces and not disperse as easily. The greatest such differences were recorded in La Bisbal del Penedès, where there was a divergence of 3.6 degrees.
In addition to recording and analysing meteorological data, the researchers also recorded the perceptions of human tower building participants regarding the most and least favourable conditions for their activities. Through participatory workshops, the research team was able to gather the opinions of 109 people from 10 different teams on the extent to which factors such as temperature, humidity, wind, sunlight intensity and rain affect their performance, especially in summer.
The participants agreed that ideal conditions were ones where the temperature and humidity are not too high, the sky is a little overcast and, of course, it is not raining or windy. In terms of temperature, they established an optimal range of 18 to 25 degrees, and an extreme threshold at 35 degrees, above which human tower building should probably not take place for the safety of both the participants and the public. This temperature was not exceeded on any of the aforementioned dates, but nevertheless the study highlights that optimal weather conditions for building human towers do not occur in summer.
Finally, the researchers support the adoption of adaptation measures suggested by the human tower builders in the face of the increasingly obvious climate situation. Faced with the worsening weather conditions in summer for building human towers-especially during the central hours of the day-and the prospect that this trend will continue in the short to medium term, participatory workshops have identified six areas in which measure could be taken, namely the dates when events take place, their duration, the physical space where they are held, food and drink for the participants, clothing for the participants and the medical provisions available.
From these areas, 45 measures have been drawn up and assessed for their priority and feasibility, and are now available for adoption by the teams and organisers. The most notable and easiest to implement are: providing fresh water, creating shade in the square, providing air-conditioned indoor spaces for the human tower builders, improving participants' clothing, adapting medical provisions, limiting the duration of the events and changing the times of day when they are held.
