Reconstruction and homogenization of the longest instrumental precipitation series in the Iberian Peninsula (Barcelona, 1786–2014)

Abstract

Detection and reconstruction of early instrumental series is an interdisciplinary activity that allows us to extend climate data records to periods prior to the mid-19th century, extending the overlapping periods with climate proxies and characterizing extreme events. In this work, the collection of several data sources corresponding to different periods and locations, obtained with a wide range of methods and instruments by institutions or private observers, provides the following results: Barcelona has a continuous rainfall series with monthly resolution since 1786 and with daily resolution since 1850. It is worth mentioning that the records from Barcelona provide the longest continuous monthly series available on rainfall in the Iberian Peninsula. The monthly records have been homogenized by using a relative homogenization approach, HOMER. The results highlight the existence of five breaks, most of them due to relocations or instrumentation changes documented in the metadata, which have been adjusted to remove non-climatic factors. The homogenized annual and winter precipitation series in Barcelona show a statistically significant increase from 1786 to 2014, although this increase is mainly due to the concentration of negative anomalies during the first half of the 19th century, which is also clearly visible in the seasonal series. Specifically, an extreme mega-drought episode was observed from the 1810s to the 1830s, which is supported by different proxy data. For a better dissemination of the homogenized monthly series developed in this study, the data set is freely available to the research community.

Long-term drought variability and trends in Barcelona (1787-2014)

“…As most long-term climatological time series are affected by multiple non climatic factors that do not allow to detect the climatic signal (Aguilar et al, 2003), quality control routines and homogenisation procedures had previously required to ensure consistency and statistical robustness to the final results. The quality control tests included in the RClimDexExtraQC software package (Aguilar and Prohom, 2010) and the HOMER homogenisation method (Mestre et al, 2013) have been applied to the monthly mean temperature and to the monthly precipitation (Prohom et al, 2015). The HOMER is a relative homogenisation method that integrates the best features from other existing methods becoming currently one of the best homogenisation method to adjust annual and monthly climate time series (Venema et al, 2012).…”

“…The HOMER is a relative homogenisation method that integrates the best features from other existing methods becoming currently one of the best homogenisation method to adjust annual and monthly climate time series (Venema et al, 2012). The adjustment of the monthly climate series of Barcelona has ensured data consistency and reliability after the comparison with other observed and reconstructed climate series in the Western Mediterranean basin (Prohom et al, 2015).…”

“…More than 60-year sub-periods were established to achieve reliable drought trends taking into account the cyclic drought occurrence (Santos et al, 2010). The sub-period 1851-2014 was chosen in order to figure out changes in drought trends when removing major dry conditions occurred in the early 19th century (Prohom et al, 2015) while the subperiod 1901-2014 was of interest to assess drought trends across the 20th century. Finally, trends computed from the sub-period 1951-2014 informed us about changes in drought patterns during the period of maximum temperature increase related to climate change (Salomon et al, 2007).…”

“…The period 1812-1838 was exceptionally dry due to a strong decrease in precipitation at annual and seasonal scale. For instance, more than 80% of annual precipitation was below the climatological mean for the period 1806-1841 (Prohom et al, 2015). This means that Barcelona was more than two decades under dry conditions with a few drought interruptions.…”

“…Under this situation, it seems crucial to know how drought patterns are changing across time in the metropolitan urban areas, such as Barcelona, where precipitation decreased slightly since 1900 (Prohom et al, 2015), while a large temperature increase is found since the end of the 18th century, especially in summer .…”