Trends in daily precipitation on the northeastern Iberian Peninsula, 1955-2006

The temporal evolution of nine daily precipitation indices over the northeastern Iberian Peninsula was analysed for the period 1955-2006, using data from 217 observatories. Cross-tabulation analysis enabled detection of statistically significant overlap among spatial distributions of trends in the study area. There was a general decrease in annual precipitation at most observatories, a decrease in the number of rainy days and precipitation intensity and an increase in the duration of dry spells. The frequency and contribution to annual precipitation of moderate and heavy rainfall events did not change at most observatories, or showed a decreasing trend in these events. There was very large spatial and seasonal variability, with implications for water management and risk assessment in the region. The decrease in precipitation was very marked in headwaters during winter and spring, potentially affecting reservoir management in the region. Heavy rainfall events generally decreased in the west of the region in winter, and in the east of the region in autumn, when these areas are more exposed to hazards related to extreme rainfall. Large differences in the sign and magnitude of trends occurred over very short distances, suggesting the need for dense networks of observatories to ensure reliable and robust detection of regional trends. © 2009 Royal Meteorological Society.