Historic seasonality in Iberian trees: 400 yrs of winter North Atlantic Oscillation and summer hydroclimate
Tuesday, 15 December 2015
Poster Hall (Moscone South)
The North Atlantic Oscillation (NAO) is Europe’s dominant mode of climate variability. Its negative phase represents a change in the westerlies that brings wet conditions to the Iberian Peninsula (IP). The NAO exhibits decadal and centennial non-stationary behaviour with high temporal variability challenging the reliability of its reconstruction and predictability. Here, we use ring-width and stable isotopes in cellulose of trees from the northwest Iberian Peninsula to link NAO and regional hydroclimate over the last 400 years. Non-linear methods based on extremes allow the capture of distinct seasonal climatic variability recorded by tree-ring parameters and asymmetric signals of the associated atmospheric features. Tree growth is largely pre-conditioned by winter-spring precipitation, rather than water availability during the growing season. Thus, wider rings allow for a skillful wintertime NAO reconstruction. In contrast, extreme values in stable isotopic records are linked to early-summer IP hydroclimatic conditions. Extreme wet/dry summers detected by these trees compare favourably to pluvial/drought episodes in historical records based on rogation ceremonies from Catholic liturgy in northeastern Spain. Independent sources of past climate variability validate our findings that attribute the non-linear moisture signals recorded by extreme tree-ring values to distinct large-scale atmospheric patterns and allow for targeted seasonal 400-yr reconstructions of wintertime NAO and summer hydroclimate variability.