The Potential of Deriving Tree-Ring-Based Field Reconstructions of Droughts and Pluvials over Fennoscandia

Moisture availability has been identified as one of the most important factors in the context of future climate change. This paper explores the potential of applying a multiproxy approach to dendroclimatology to infer the twentieth-century moisture variability over Fennoscandia. Fields of the warm-season (June-August) standardized precipitation evapotranspiration index (SPEI) were developed from a dense network of precipitation-sensitive annually resolved tree-ring width (TRW), maximum density (MXD), and stable carbon (delta C-13) and oxygen (delta O-18) isotope chronologies using a point-by-point local regression technique (PPR). Two different approaches were tested for selecting candidate tree-ring predictors of SPEI for each gridpoint reconstruction: a search radius method and a search spatial correlation contour method. As confirmed by a range of metrics of reconstruction fidelity, both methods produced reconstructions showing a remarkably high accuracy in a temporal sense, but with some minor regional differences. As a whole, the spatial skill of the reconstructed fields was generally quite good, showing the greatest performance in the central and southern parts of the target region. Lower reconstruction skills were observed in northern part of the study domain. Regional-scale moisture anomalies were best captured by the reconstructions, while local-scale features were not as well represented. The authors speculate that a spatially and temporally varying tree-ring proxy response to temperature and precipitation in the region may cause some uncertainties in a Fennoscandian hydroclimatic reconstruction; this needs further investigation. Overall, this study shows a great potential for making long-term spatiotemporal reconstructions of moisture variability for the Fennoscandian region using tree-ring data.