The recently completed 2023 has once again been a very dry year in Barcelona and other places in Catalonia, especially in its eastern half. The Fabra Observatory of Barcelona, belonging to one of the oldest institutions in the city, the Royal Academy of Sciences and Arts of Barcelona (RACAB), has once again totaled, after two years, 2021 and 2022, also very dry, just over 300 mm of precipitation.
Specifically, 309.5 mm, which is only a little more than half of the observatory's average (611.8 mm). An amount like that mentioned is comparable to the normal amounts in many places in the southeast of the Iberian Peninsula or the Monegros region, very dry geographical areas, whose landscapes reveal a marked aridity.
The value of annual precipitation places 2023 as the second driest year in the 110-year rainfall series, from 1914, when meteorological records began at the Fabra observatory, to the present.
But the highlight is the concatenation of the three driest years, 2021, with 327.6 mm, 2022, with 307.7 mm and 2023, with the aforementioned amount. Randomly, the fact that the three driest years appear in a row in the 110-year series, whatever their order and anywhere in it, has a very small probability of occurrence. It constitutes what in meteorology is called an anniversary, that is, a relevant or striking meteorological event or event due to its climatological, historical or merely anecdotal value.
If, in addition, it is required that the three driest years occupy, whatever their order, the end of the series, as has occurred, their probability is negligible. The above has resulted in a truly exceptional meteorological drought, whose return period is very long, secular. This has led to a hydrological drought, expressed by the meager percentages of water stored in the reservoirs of the internal basins of Catalonia, compared to their maximum capacity, below 17% at the beginning of 2024, with no previous reference.
The scarcity of water, in turn, has given rise to an agricultural or edaphic drought, due to its impact on the soil and agriculture, as well as an ecological drought, with severe effects on some ecosystems. And, finally, a period of socioeconomic drought has been entered, as a good number of economic sectors and daily activities have been affected by the decrease in available funds.
Does the current situation, due to the recent concatenation of the three driest years, allow, from a climatological point of view, to affirm that the annual precipitation in Barcelona already shows a negative trend, that is, towards a statistically significant reduction?
To answer this question, statistical tests of trends are used, of which the most universal is the non-parametric Mann-Kendall test.
Well, when applied to the entire series, as well as to the last 100 years, 30, 25 and 20, it cannot be said that there is a negative trend in annual rainfall in the Catalan capital. However, if a series with approximately 50 years in length is considered, ending in 2023, that is, beginning in the 70s of the last century, the aforementioned test does admit that in the last half century the precipitation in Barcelona presents a statistically significant reduction trend, with a confidence level in some cases of 95% (for example, for the 53-year period 1971-2023).
This is so, because some of the years of the aforementioned decade, that is, the beginning of the period, were particularly rainy, such as 1971, the rainiest since there are records at the Fabra observatory, with 1,122.5 mm, and, in At the other extreme, the last three have been the driest.
The marked rainfall shortage of the last three years in Barcelona, as well as in other Catalan cities, is even more serious due to the fact that the last two years have been, at the Fabra observatory, the warmest since its inception, something explainable largely due to global and regional warming.
On an annual scale, one could speak of a combined dry-hot event, which is currently the subject of cutting-edge research in climatology in the case of heat waves that occur during a period of drought.
Javier Martín-Vide is a professor of Physical Geography at the University of Barcelona
