13 Projections of EMME annual precipitation anomalies

4.2. Precipitation – averages and extremes

Global warming is associated with the Hadley Cell circulation expansion and the poleward shift of the westerlies and associated storm tracks (IPCC, 2013). This creates easterly wind anomalies at the mid-latitudes (Lu et al., 2007). Normally, westerlies are associated with moisture convergence in Mediterranean latitudes; however, the easterly shift weakens this phenomenon and induces drying (Seager et al., 2019). About 85% of the reduction in precipitation during the wet season, averaged across the Mediterranean, is attributed to such atmospheric circulation responses (Zappa et al., 2015). In addition, the drying of the eastern Mediterranean is largely caused by enhanced warming over land (Drobinski et al., 2020).

Time series of annual precipitation anomalies (with respect to the 1986-2005 climatic means), averaged for the EMME region, are presented in Figure 13. The inter-annual variability and spread of the model results are more pronounced than of annual temperatures, highlighting the greater uncertainty of precipitation projections. For RCP2.6, no significant change in precipitation is projected. In contrast, the business-as-usual RCP8.5 projects a 10-20% precipitation decrease for the region by the end of the century. For the eastern Mediterranean, this range is in very good agreement with other assessments, suggesting that the mean rate of the decrease in land precipitation across the Mediterranean is 4% per degree of global warming (Cherif et al., 2020). In addition to the overall drying trend,

FIGURE 13. Projections of EMME annual precipitation anomalies (for the 1986-2005 reference period)

Source: Based on CORDEX-CORE climate projections and two Representative Concentration Pathways.