A study analyses the quality of the last two centuries of rain records in Catalonia
Catalonia has daily and continuing data on the rain since 1855, before the first modern meteorological stations were opened and standardized measures were taken. The reliability of these data is essential to understand the effects of the climate change in this area. Therefore, a team of researchers from the University of Barcelona and the Technical University of Catalonia · BarcelonaTech, in collaboration with the Meteorological Service of Catalonia, have carried out a study to analyse the quality of rain databases in Catalonia. The study, published in Theoretical and Applied Climatology, presents a new quality control process for daily rain data after having tested it with more than ten million data from 1,726 meteorological data in Catalonia.
Catalonia has daily and continuing data on the rain since 1855, before the first modern meteorological stations were opened and standardized measures were taken. The reliability of these data is essential to understand the effects of the climate change in this area. Therefore, a team of researchers from the University of Barcelona and the Technical University of Catalonia · BarcelonaTech, in collaboration with the Meteorological Service of Catalonia, have carried out a study to analyse the quality of rain databases in Catalonia. The study, published in Theoretical and Applied Climatology, presents a new quality control process for daily rain data after having tested it with more than ten million data from 1,726 meteorological data in Catalonia.
After applying this new quality control system, the amount of days in which the precipitation value can be considered valid ranges from 83.6% to 99.6%. The study also shows 47% of the series with ten years of operation (1,110 series) present an excellent quality, a percentage that reaches 78% if considering the good quality ones. Regarding the series with a minimum length of thirty years (347 series), 32% have an excellent quality and 66% a good quality.
“Rain data at the beginning of the analysed period were quality ones already”, notes Alba Llabrés, first author of the study. “During the observational history of Catalonia there has always been a great amount of series with good temporary coverage, although there are certain periods with an increase in the number of measure points with no quality control that alter the global average quality in the series as a whole”, notes the expert.
According to Llambrés, at the beginning of the analysed period (1855-1865), “there was no automatic relative analysis due the lack of reference series; but absolute indexes on quality provide good results for this initial series, listed in the average quality values of current observations”. The only data on rainfalls for this first period are the ones from the station of the University of Barcelona, which was in Carme street (carrer del Carme). During the following period, that goes from the end of Civil War on, “there are good series, but if considering all available ones, the average quality is lower”. After the years 1960-1970, “the average quality, regarding all the available series, reaches acceptable values and increases up to this date”, concludes Llabrés.
The used process by the researchers compares daily data with stations or reference data automatically selected after an initial estimation of the quality and a proximity study on the location and correlation. The results can be verified thanks to the Automatic Meteorological Station Network (XEMA) managed by the Meteorological Service of Catalonia, in which quality is controlled daily.
The designed control of quality provides good results and can be applied to data from different places, ranging from last century meteorological stations to manual historical measurements. Once applied, a selection of series with the required quality is taken to work on future specific meteorological studies.
University station
Although the first systematic meteorological observations in Catalonia -and in the Iberian Peninsula- date back to 1780 (carried out by doctor Francesc Salvà), daily data on rain are available since 1855, and are now added to the database of the Meteorological Service of Catalonia. The meteorological station that enabled these records is the one in the bell tower of the former monastery of Carmelites (carrer del Carme, 40), head office of the University of Barcelona since 1845. According to an inventory of UB Professor of Physics Antoni Rave, in the Records Office of the University, thermometers were placed in the tower of the building, the vane was in the tower roof and the barometer was in the bureau of Physics, in the main floor. Also, there were two rain gauges, one on top of the building and the other in the ground floor, the most used one.
According to information published in the journal El Cultivador (vol 1-5, 1848-1852), there could have been data before 1855, at least in 1848, but at the moment the Meteorological Service of Catalonia has only added the records of the database from 1855 on. “In the 19th Century, measures were carried out by people interested in meteorology and particularly doctors who recorded rain data to get conclusions of the effect the meteorological conditions have on health”, notes Llabrés. The fact that Catalonia has such a wide volume of series and wide temporal coverage is mainly due the task carried out by the Meteorological Service of Catalonia.
Article reference:
Llabrés-Brustenga, A.; Rius, A.; Rodríguez-Solà, R.; Casas-Castillo, M. C., i Redaño, A. “Quality control process of the daily rainfall series available in Catalonia from 1855 to the present”. Theoretical and Applied Climatology, January, 2019. DOI: 10.1007/s00704-019-02772-5