The last Annual Bulletin of Climate Indicators of Meteorological Service of Catalonia confirms with numbers that nowadays the plants bloom before –19 days in the case of the olive tree–, that the fruits ripen before –37 days in the pear tree–, that the leaves of the trees fall later –23 days in the apple tree– and that the birds arrive before –24 days in the case of the barn swallow–, in comparison to the early 1970s. Due to their close relationship with the climate, these changes in the rhythm of nature prove unequivocally that the weather is changing.

The Meteorological Service of Catalonia (SMC) has published the twelfth edition of the Annual Bulletin of Climate Indicators (BAIC 2018) that analyzes the climate of Catalonia in recent years. This report includes phenological data –the manifestations of living beings bound to the climate– collected in La Serra d’Almos (Ribera d’Ebre), such as the date of flowering, the ripening of the fruits, the fall of the leaves or the date of migration of the birds. These manifestations or rhythms of nature are so sensitive to climate variations that their alteration tells us that the weather is changing.

The most spectacular phenological data of all the data analyzed is the ripening date of the pear, which is produced now 37 days earlier than in 1971, when the first observations were made. This means that every 10 years the pears ripen eight days earlier. In the case of apricot tree, its fruits now ripen 28 days before than in 1972 (this event is produced 6 days before in each decade). This means that 47 years ago, the apricots ripened on average around June 21st and now they do it around May 24th.

Regarding the flowering, the most affected plant is the olive tree, which blooms 19 days before than in 1973 (4 days before in each decade). It flowered around June 3rd 46 years ago, and the date has moved to the May 15th nowadays. The vineyard also blooms before, specifically 11 days earlier than in 1971 (2 days/decade).

Evolution in the date of the ripening of the apricot (graph 1) and the date of the flowering of the olive tree (graph 2) in La Serra d’Almos (Ribera d’Ebre) from 1971 to 2018. The green line corresponds to the day of the year (of 365) in which the phenological manifestation is observed and the black line is the trend (a kind of average) that draws this behavior. In this straight line you can see how the ripening of the apricot tends to move forward six days every 10 years and that the flowering of the olive tree does it four days before every 10 years.
The leaves of the trees also fall later in the autumn

The apple tree case is the most important of all of them, since it now loses the leaves 23 days later than in 1971 (this event is delayed 5 days every decade). This means that if 48 years ago it lost the leaves around November 21st, nowadays it is doing it around Christmas, on December 14th approximately. The second species most affected in the fall of the leaves is the pear tree, with a delay of 20 days in comparison to 1971 (4 days / decade).

Evolution of the date of the fall of the leaves in the apple tree in La Serra d’Almos (Ribera d’Ebre) from 1971 to 2018. The green line corresponds to the day of the year (of 365) in which it is observed the fall of the leaves and the black line is the trend (a kind of average) that draws this behavior. One can observe how the fall of the leaves goes through five days every 10 years.

The effects of climate change can also be observed in the animals. This is the case of the barn swallow (Hirundo rustica) that now arrives 24 days before (5 days before every decade) but also it leaves 22 days before (4.5 days/decade).

Phenology depends more on temperature than on precipitation

If we compare the dates of the phenological manifestations and the temperature, it has been seen that these two factors are very well related. For example, the bloom of the olive tree adjusts very well to the average of the maximum temperatures of the year, and the ripening of the apricot is very well related to the average of the maximum temperatures in spring. That is, these plants bloom and ripen before the warmer years.

In the same line, the fall of the leaves of the apple tree is related to the average temperature of the autumn. Therefore, the more heat it does in autumn, the more the fall of the leaves is delayed.

 

Relation between the flowering of the olive tree and the average of the maximum temperatures throughout the year (TX Anual) (graph 4), between the ripening of the apricot and the average of the maximum temperatures in spring (TX Primavera) (graph 5), and between the fall of the leaves of the apple tree and the average temperature in autumn (TMIT Tardor) (graph 6) in La Serra d’Almos since the beginning of the 1970’s. The blue rhombuses indicate the temperature reached the day of the year in which the phenological manifestation happened. The black line is the regression line (a kind of average) that draws each behavior. The “degree of robustness” of the relationship is numerically represented by R2: the closer to the 1 is it value, the better the correlation is. The conclusion is that phenology depends on temperature.

On the other hand, these connections are not so direct when the same analysis is made with annual precipitation or the season of the year. Therefore, it can be concluded that phenology is more affected by changes in temperature, and not by precipitation variations.

The key to the study of phenology is the perseverance

All these conclusions can be obtained if there are phenological observations taken continuously for many years in a row. This is the case of the phenological database that has been used to prepare the BAIC report. These are the observations of Josep Borrell, who voluntarily has written down all these rhythms of nature constantly for almost 50 years in La Serra d’Almos, located in Ribera d’Ebre (Catalonia).

Moreover, these conclusions are representative of the rest of Catalonia, because the evolution of the climate in La Serra d’Almos is similar to the evolution in the rest of the country, and the phenological behavior in other places of Catalonia that have data is similar to the one produced in this municipality.

In the BAIC 2018 report, it is also confirmed that the average annual air temperature has been increased in 1.6 °C in the last 69 years, at a rate of 0.25 °C per decade, and now it rains on average 57 mm less per year. This means that every 10 years it rains a 1.4 % less (although this data does not have enough statistical robustness). It is also confirmed that the sea temperature increases at a rate of 0.3 °C/decade at 50 m depth, and also that the sea level rises at a rate of 3.3 cm every 10 years. You can consult a more detailed summary of these and other data in the press release of the SMC on the BAIC 2018 report.

 

Pear tree in bloom and with the blossoming leaves observed on 16th March 2019 by Xavier de Yzaguirre, observer of RitmeNatura at Natusfera (CC BY-NC 3.0)
Join RitmeNatura so that scientists can study the climate change

RitmeNatura is a citizen science project that gathers data and phenological observations in Catalonia. Collected by citizens, these data are offered for consultation in real time in order to make them useful for scientists and managers.

Natusfera is the tool used by RitmeNatura to collect the phenological observations shared by the citizens. These observations can be of two types: recurrent or occasional. The recurrent and continuous observations in time on the same living organism, animal or plant species, or in the same area, is the best way to collect phenological information, as this method provides more information about the rhythm of nature and how it changes.

However, all the observations give information: occasional observations that citizens make in their environment are also collected day-to-day.

Create a Natusfera user, join the two subprojects and follow the rhythm of nature!

Header photo: ripening pears. Author: joseluisromero in Natusfera (CC BY-NC 3.0)

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