title: Northern Hemisphere hydroclimate variability over the past twelve centuries.
abstract: Accurate modelling and prediction of the local to continental-scale hydroclimate response to global warming is essential given the strong impact of hydroclimate on ecosystem functioning, crop yields, water resources, and economic security. However, uncertainty in hydroclimate projections remains large, in part due to the short length of instrumental measurements available with which to assess climate models. Here we present a spatial reconstruction of hydroclimate variability over the past twelve centuries across the Northern Hemisphere derived from a network of 196 at least millennium-long proxy records. We use this reconstruction to place recent hydrological changes and future precipitation scenarios in a long-term context of spatially resolved and temporally persistent hydroclimate patterns. We find a larger percentage of land area with relatively wetter conditions in the ninth to eleventh and the twentieth centuries, whereas drier conditions are more widespread between the twelfth and nineteenth centuries. Our reconstruction reveals that prominent seesaw patterns of alternating moisture regimes observed in instrumental data across the Mediterranean, western USA, and China have operated consistently over the past twelve centuries. Using an updated compilation of 128 temperature proxy records, we assess the relationship between the reconstructed centennial-scale Northern Hemisphere hydroclimate and temperature variability. Even though dry and wet conditions occurred over extensive areas under both warm and cold climate regimes, a statistically significant co-variability of hydroclimate and temperature is evident for particular regions. We compare the reconstructed hydroclimate anomalies with coupled atmosphere-ocean general circulation model simulations and find reasonable agreement during pre-industrial times. However, the intensification of the twentieth-century-mean hydroclimate anomalies in the simulations, as compared to previous centuries, is not supported by our new multi-proxy reconstruction. This finding suggests that much work remains before we can model hydroclimate variability accurately, and highlights the importance of using palaeoclimate data to place recent and predicted hydroclimate changes in a millennium-long context.
authors.affiliation: Department of History, Stockholm University, SE-10691 Stockholm, Sweden.|Centre for Medieval Studies, Stockholm University, SE-10691 Stockholm, Sweden.|Bolin Centre for Climate Research, Stockholm University, SE-10691 Stockholm, Sweden.
authors.forename: Fredrik Charpentier
authors.initials: FC
authors.lastname: Ljungqvist
authors.affiliation: Navarino Environmental Observatory, GR-24001 Messinia, Greece.|Department of Physical Geography, Stockholm University, SE-10691 Stockholm, Sweden.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Krusic
authors.affiliation: Bolin Centre for Climate Research, Stockholm University, SE-10691 Stockholm, Sweden.|Department of Physical Geography, Stockholm University, SE-10691 Stockholm, Sweden.
authors.forename: Hanna S
authors.initials: HS
authors.lastname: Sundqvist
authors.affiliation: Helmholtz-Zentrum Geesthacht, Institute for Coastal Research, DE-21502 Geesthacht, Germany.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Zorita
authors.affiliation: Bolin Centre for Climate Research, Stockholm University, SE-10691 Stockholm, Sweden.|Department of Mathematics, Stockholm University, SE-10691 Stockholm, Sweden.
authors.forename: Gudrun
authors.initials: G
authors.lastname: Brattström
authors.affiliation: Swiss Federal Research Institute WSL, CH-8903 Birmensdorf, Switzerland.
authors.forename: David
authors.initials: D
authors.lastname: Frank
mesh_terms: D001272:Atmosphere; D002681:China; D002980:Climate; D057231:Climate Change / Q000706:statistics & numerical data*; D017753:Ecosystem; D062305:Geographic Mapping; D019015:Geologic Sediments / Q000737:chemistry; D049668:History, 15th Century; D049669:History, 16th Century; D049670:History, 17th Century; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D049691:History, Medieval; D062070:Hydrology; D007053:Ice / Q000032:analysis; D019083:Mediterranean Region; D008962:Models, Theoretical; D011891:Rain; D012987:Soil / Q000737:chemistry; D062211:Spatio-Temporal Analysis; D013696:Temperature; D014197:Trees / Q000033:anatomy & histology / Q000254:growth & development; D035501:Uncertainty; D014481:United States
chemical_list: D007053:Ice; D012987:Soil