# Vegetation Productivity Losses Linked to Mediterranean Hot and Dry Events
## 4 Discussion  
The European part of the Mediterranean basin is a climate change hotspot for droughts, heatwaves [1,8] and other extreme events. Several studies have identified a high risk for increased water stress on crops and natural ecosystems over a broader area of the southern sectors of Europe, the Mediterranean, the Middle East and North Africa [56,57]. We analysed the ecological response to the occurrence of hot and dry events in the European part of the Mediterranean basin's vegetation productivity, with particular emphasis on the most severe episodes that occurred in the Iberian Peninsula, Eastern Mediterranean and Western Europe between 2001 and 2019. Our results showed that the episodes which occurred in the Iberian Peninsula in 2005 and 2012 led to an extreme ecological response from the vegetation. The land cover of this region is quite adapted to water-limited conditions, especially in summer [58]. However, [10,12] we were able to pinpoint that the 2005 drought in IB started in the fall of 2004 and [59] traced the take-off of the 2012 drought back to the fall/winter of 2011. Therefore, the cumulative effect of persistent drought for several months might have driven vegetation to consecutive productivity deficits, agreeing with [60,61] that highlighted the dependence of vegetation on water availability in IB. On the other hand, the comparison between the correlations of SM-GPP, LST-GPP and also SM-LST anomalies, across all land cover types during summer, suggested that high LST anomalies played an important role in the amplification of ecological stress in 2005, not only due to the strong effect of high summer temperatures on soil moisture depletion but also possibly due to a direct negative effect of heat stress (from high LST) on GPP. The coupling of SM and LST verified that soil moisture-temperature feedback has a clear influence on vegetation, as clearly pointed out by [24]. We have shown in the IB studied cases that productivity in croplands and low tree cover areas is reduced more rapidly in response to dry spring conditions, while high tree cover areas showed negative GPP anomalies later, in summer. These results agree with [62,63], who observed that in water-limited environments, forests tend to develop deeper roots, which may allow them to access deeper soil water, increasing their resistance to short-term drought. A point that should be elevated here is related to the intra-seasonal variability of GPP. In IB, the negative correlation between LST-GPP anomalies and positive correlation between SM-GPP anomalies, both in the spring, indicated an already a water-limited regime in this season, which is consistent with the prolonged drought situations. In the IB 2012 episode, a negative correlation between SM-GPP in the spring was found in high tree cover areas, contrary to the other land cover types that showed weak SM-GPP and LST-GPP relationships (Table S1). The negative correlation can be possibly linked to the strong negative temperature anomalies (\(-5\,^{\circ}\)C) in April in high forest cover areas. These results may be linked to spring frost at night which could result in leaf or bud damage during the early growing season and may affect vegetation productivity throughout the year [64]. The results of the Eastern Mediterranean and Western Europe studied cases found an amplification of the GPP anomalies during the summer. The exacerbation of negative GPP may be linked to compounding hot and dry summer conditions. For instance, in WE, the large GPP anomalies were associated with summer heatwaves, both during 2003 [18,65,66] and 2006 [67]. Moreover, the correlation results in 2006 may suggest the concurrency of hot and dry conditions in the summer, caused by the July heatwave [67] and the soil moisture depletion, which led to strong reductions in GPP anomalies. These results in EM and WE enhance the influence of heat-drought coupling on vegetation productivity. An important aspect that should be stressed is the link between spring conditions and hot summers.