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.

Spatio-temporal variability of Arctic summer temperatures over the past two millennia: an overview of the last major climate anomalies

“…They argue that the medieval warming in the Arctic did not extend to Greenland, thus challenging our long-held understanding of the settlement and later abandonment of Norse Greenland. This is in direct contradiction to the spatial temperature reconstructions of Mann et al (2009) and Ljungqvist et al (2012Ljungqvist et al ( , 2016, which instead point to very warm conditions in Greenland at that time. As we will see, our results show that the Greenland sector of the Arctic indeed was warm during the 10 th and especially the early 11 th centuries CE.…”

Holocene paleohydrological reconstruction of Lake Strzeszyńskie (western Poland) and its implications for the central European climatic transition zone

“…The central European transitional climate zone migrated over central Europe on decadal to millennial time-scales, mostly due to external forcing mechanisms (Ljungqvist et al 2016). However, the complex reconstruction teleconnections amongst the cryosphere, ocean and atmosphere are often biased by more-local influences in terrestrial records (Magny 2004).…”

Summer temperature and drought co-variability

“…Rehfeld and Laepple (2016) found that the linkage between temperature and precipitation over Asia is timescale dependent, and that model simulations agree with proxy data on shorter timescales but disagree on longer timescales. these results, together with the Northern Hemispheric proxy-model comparison by Ljungqvist et al (2016), indicate that the hydroclimate responses to low-frequency temperature changes are not yet sufficiently well known.…”