Characterisation and temporal evolution (1915-2022) of drought and pluvial periods in Catalonia

Catalonia is currently affected by a severe drought episode which is reporting unrecorded impacts in most part of the country. It is well known that precipitation presents a high temporal variability in the Mediterranean climate. Consequently, drought episodes are frequent, and they are an intrinsic characteristic of this type of climate. However, drought events are showing a higher frequency during the last few decades.

In this work we have studied drought and pluvial episodes derived from the calculation of the Standardized Precipitation Index (SPI) in Catalonia during the instrumental period 1915-2022. Series of precipitation aggregated at 12 and 72 months, lead to a first approximation for temporal variability of drought and pluvial events at high and low frequency, respectively. From the temporal evolution of the SPI-12, it is derived that the frequency of dry(wet) episodes has increased(decreased) in recent decades (statistically significant). This behaviour is observed in all Catalan hydrological catchments. The increase in the drought frequency is also corroborated when analysing the SPI-72 dry/wet area time series. The SPI-72 signal also reveals that the natural transition between pluvial and drought periods (and vice versa) has been broken since the 1980s, with domination of droughts since then. From the total number of drought episodes, two of them emerge: the 2004-2008 event and the current 2021-2023 drought episode. Depending on the analysed basin, one of these events can be considered the most severe one ever recorded in Catalonia since 1915.

In fact, the severity of the current event has motivated the creation of a new drought severity index (DSI), which considers the pick, mean intensity, duration and extension of the drought area. In the context of climate change, this index is called to be useful to rank future drought episodes when compared with historical ones.