Identification of forest vulnerability to droughts in the Iberian Peninsula

Abstract The increase in frequency, severity, and duration of droughts poses as a serious issue to the management of forests in the Iberian Peninsula, with particular emphasis on the decline of forest growth and forest dieback. Hence, the adoption of adaptation and mitigation measures in forest ecosystems that are more vulnerable to drought is a pressing matter that needs to be addressed in the near future. This work aims at identifying the regions in the Iberian Peninsula where forest exhibit high vulnerability to drought conditions. To accomplish that, a vulnerability map is produced by considering three pillar components: exposure, sensitivity, and adaptive capacity to drought. Exposure is estimated based on the multi-scalar drought index Standardized Precipitation-Evapotranspiration Index (SPEI) and aridity, while the remotely sensed Vegetation Health Index (VHI) and mean forested cover are used to assess the regions’ sensitivity to drought. Finally, elevation, water table depth, fire radiative energy, and annual solar irradiation are compiled as indicators to assess adaptive capacity. Principal component analysis was then applied to the three pillar components to identify the areas more vulnerable to drought. This approach allows for the identification of forested areas vulnerable to drought in terms of vulnerability classes automatically determined. Forests presented very high vulnerability in eastern Spain, and central Portugal. Within the most vulnerable vegetation communities, mosaic tree and shrub types revealed to be extremely vulnerable to droughts in the Iberian Peninsula, followed by needle-leaved forests (in Central Portugal, and Northeast Iberia). This work highlights the regions and primary vegetation communities to which the effort of adapting and mitigating drought consequences should be utterly enforced by the responsible authorities.