The scientist who will reconstruct a thousand years of droughts in Spain with beams from farmhouses and data from the Church

The project of postdoctoral researcher Marie Curie in Geology at the National Museum of Natural Sciences (MNCN-CSIC) is called ‘Medirings’. It has financial support from a Leonardo Scientific Research Scholarship from the BBVA Foundation. Tejedor believes that, when the millennial reconstruction is completed, it will be a good tool to find out to what extent the current droughts are part of the natural variability of the Mediterranean climate or if, on the contrary, they have been modified by climate change. “We don’t know very well if we are increasing the probability that (a drought) will occur by 30 or 50%,” he exemplifies.

But getting the ideal record for rebuild the Mediterranean ‘hydroclimate’ It’s not easy. In Spain there is good meteorological data collected from the last 60 or 70 years, which has been recorded through different instruments and technologies. But they fall very short. Furthermore, explains Tejedor, in this period the climate could already be disturbed by the accumulation of greenhouse gases in the atmosphere, which began in 1850. So we have to go back further to obtain unadulterated data, in addition to having a representative sample. «What we are trying to do is know what climate variability is like before having recorded data and for that we have to go to other sources. One of the best is tree rings,” he explains.

If there is a very severe drought one year, the tree does not have sufficient water and nutrient resources and does not grow. Thus, the ring that draws the inside of the trunk is very narrow. And this doesn’t just happen in one tree, it happens in the entire forest affected by that drought, so it is easily identifiable. “Then we relate it to the climate that we know through instrumental data, the 60 or 70 years that we have,” says the researcher. This way they are able to date each ring, and go back beyond the last 70 years.

Teruel farmhouses

The team has already done a reconstruction of the last 300 years. «It is seen that 2023 is the driest year of the last almost 300 years,” says Tejedor. However, this reconstruction has been done with live trees. But to go back a millennium they have to look for older woods. And they have found a mine in the Teruel Maestrazgo. There the farmhouses, mills and churches that were built in medieval times with wood from the area continue to house the original beams. “It is the best we can achieve to understand the climate of the past,” says Tejedor. Pine trees from the area were used, which also gives a good example of the Mediterranean hydroclimate.

With the search for old farmhouses they have also created a curious competition between the owners of the buildings in the area, who now want to find out If yours is older than your neighbor’s. In exchange, they just have to let Tejedor’s team extract a strip from one of the beams of the house with a kind of drill bit.

It is with these samples that they will reconstruct the climate since the most recent period in time to the most distant, overlapping the years they already know with those that remain to be reconstructed. They believe there are hidden woods in the area dating back to the 18th century. until the 12th century. “We already have a sample that is from 1357. They are buildings that were like castles, the constructions there are impressive,” says Tejedor.

Prayers

Some farmhouses have the year of construction inscribed in stone, which makes the work easier, but they are a minority. In the rest of the cases, researchers will have to find the similarity of a ring with that of another tree that they have managed to date.

Even so, to verify their data the researchers give up nothing. The work of overlapping tree rings is sometimes complemented with carbon 14. But, above all, with Church documents, which have proven to be very useful and an invaluable source of information. In its archive, the well-known rogations have been recorded, ceremonies that could be to ask for precipitation (pro pluvia), when the drought was causing havoc, or to ask for the storms to stop (pro serenitate).

“We have been doing prayers in Spain since the 12th century continuously until last year, which they did in Gerona in a ceremonial way,” exemplifies Tejedor. Much of this data has been collected in previous research, and is now used to verify the ‘natural’ record of the trees. “It is a way to validate the two records,” concludes the researcher.