Moisture Source Analysis of Two Case Studies of Major Extreme Precipitation Events in Summer in the Iberian Peninsula

Abstract

Extreme summer precipitation events commonly affect the Iberian Peninsula (IP), and studying the moisture sources that generate intense precipitation is extremely important. Therefore, this study analyzed the moisture sources of two major extreme precipitation events in summer in the IP. The events occurred on 18 September 1999 and 7 September 1989, and the anomalies of the associated meteorological variables are shown with respect to a 30-year reference period (1985–2014). A Lagrangian approach is used for determining the moisture source pattern using only the precipitating particles that reach the target region. In this research a dynamic downscaling methodology is applied using the WRF-ARW model forced using the ERA5 reanalysis and then the WRF-ARW outputs used to force the Lagrangian dispersion model FLEXPART-WRF. Specifically, the first event was associated with an atmospheric river favoring strong moisture transport from remote sources and the second event was caused by local convergence of moisture under the influence of a cut-off low system. For the 18 September 1999 case study, the major contribution to moisture reaching the target region was associated with the central and eastern North Atlantic, with values of up to approximately 32%. In addition, the moisture source pattern exhibited a strong anomaly in the climatological pattern. However, the origin of the moisture sources associated with the case of 7 September 1989 was mainly the western Mediterranean Sea, with a contribution of up to 40% or higher. Finally, Northwest Africa and precipitation recycling processes over the IP contributed approximately 16% to the moisture supply for this event.