Long term context for recent drought in northwestern Africa

Anthropogenic climate change is projected to exacerbate midlatitude aridity. Here, we analyze newly developed multi-century tree-ring records for a long-term perspective on drought in Tunisia and Algeria. We use a new set of 13 Cedrus atlantica and Pinus halepensis chronologies with a strong signal for warm-season drought (May-August) to generate a robust, well-validated reconstruction of the Palmer Drought Severity Index (PDSI) for the period AD 1456-2002. Key features of the reconstruction reveal the magnitude of pre-instrumental droughts from the historic record. Remarkably, the most recent drought (1999-2002) appears to be the worst since at least the middle of the 15th century. This drought is consistent with the early signature of a transition to more arid midlatitude conditions, as projected by general circulation models.