Quantifying moisture and sensible heat flux anomalies for compound drought and heat wave events in the Iberian Peninsula

Compound drought and heat wave events (CDHWs) are weather and climate hazards whose frequency is increasing in many regions across the globe. Here, we applied a novel Lagrangian atmospheric moisture and heat tracking framework to the outputs of the Lagrangian FLEXPART model driven by the ERA5 reanalysis to quantify the moisture and sensible heat flux anomalies for CDHWs occurred in the Iberian Peninsula in the extended summer (May–October) from 1991 to 2022. CDHWs are identified based on the 95th percentile of daily maximum and minimum temperatures and the self-calibrating Effective Drought Index. The Lagrangian framework is then applied to the top 20 CDHWs affecting more than 50% of continental Iberian Peninsula. Our analysis reveals that these events endure on average 10.35 days, with 2022 achieving the highest number of days (46 days) under dry and hot conditions. CDHW events are generally associated with blocking situations and high-pressure systems, whose effects can be amplified by the local land-atmosphere feedback. The results indicate that the Iberian Peninsula itself is the principal moisture source for the low summertime precipitation, followed by the North Atlantic Ocean corridor and the western Mediterranean Sea, but their total moisture contribution decreases by about 56% during the CDHWs. Moreover, the sensible heat sources pattern exhibits a local-to-regional origin, with ∼35% above the climatological value during the dry and hot events. Overall, this study provides new insight into the underlying mechanisms of CDHWs, which could be useful for helping in understanding these events in the context of global warming.