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

Abstract

Long-term drought variability and trends were assessed in Barcelona at annual and seasonal scale for the period 1787-2014 and sub-periods 1851-2014, 1901-2014 and 1951-2014 to identify changes in drought patterns across time. High quality and adjusted monthly temperature and precipitation series were required for this purpose. The Standardized Precipitation Index (SPI), based on precipitation, and the Standardized Precipitation Evapotranspiration Index (SPEI), based on the difference between precipitation and reference evapotranspiration (ET0), were calculated to describe temporal drought fluctuations. Therefore, major droughts and wet events were identified and an accurate analysis of drought severity, magnitude and duration were also carried out.Both drought indices provided similar results related to drought variability and trends in Barcelona across time, although the SPEI showed larger drought severity than SPI especially during the second half of the 20th century. Trends analysis revealed a significant drying trend at annual scale according to the SPEI since mid-19th century while the SPI did not show changes in drought patterns. At seasonal scale, both the SPI and SPEI found a clear drying trend only for summer (JJA) during the current period (1951-2014), although the SPEI was indicating the trend towards drier conditions for the whole period (1787-2014). Drought severity in SPEI series increased 13% during the second half of the 20th century compared with the whole period under study while drought magnitude and duration did not present significant changes in both the SPI and SPEI series. The increasing atmospheric evaporative demand associated to the large temperature rising experienced in Barcelona during the last decades could have played a substantial role in explaining the increase of drought severity and trends found in the SPEI series.