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Modeling 12 Centuries of Northern Hemispheric Hydroclimate

Paper Reviewed
Ljungqvist, F.C., Krusic, P.J., Sundqvist, H.S., Zorita, E., Brattstrom, G. and Frank, D. 2016. Northern Hemisphere hydroclimate variability over the past twelve centuries. Nature 532: 10.1038/nature17418.

Introducing their work, Ljungqvist et al. (2016) write that "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." But they also note that "uncertainty in hydroclimate projections remains large," due in part to the short length of the instrumental hydroclimate records that are available to assess the hind-casting abilities of today's climate models. And they thus go on to describe how they developed a spatial reconstruction of Northern Hemispheric hydroclimate variability over the past twelve centuries, shown below, which they derived from a network of 196 millennium-long proxy hydroclimate records. And what did this ambitious undertaking reveal?

Time series derived from the reconstructed gridded weighted hydroclimate anomalies, showing the fraction of land area exceeding a given wetness or dryness threshold. The red horizontal bars denote the 50% levels. Anomalies are shown relative to the centennial mean and standard deviation over the eleventh to the nineteenth centuries. Source: Ljungqvist et al. (2016).

The six scientists -- hailing from Germany, Greece, Sweden and Switzerland -- report that (1,2) "proxy evidence does not support the tendency in simulations for wet regions to become wetter and dry regions drier in a warmer climate," that (3) their "hydroclimate reconstruction does not support a general unprecedented intensification of the hydrological cycle in the twentieth century, associated with both more extreme wet and dry conditions, as simulated by an ensemble of models," and that (4) "this finding is in line with recent analyses of instrumental data reporting limited evidence for an intensification of wet and dry anomalies under current global warming," citing the findings of Sheffield et al. (2012), Greve et al. (2014) and DeAngelis et al. (2015).

And so it is that Ljungqvist et al. conclude 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."

DeAngelis, A.M., Qu, X., Zelinka, M.D. and Hall, A. 2015. An observational radiative constraint on hydrologic cycle intensification. Nature 528: 249-253.

Greve, P., Orlowsky, B., Mueller, B., Sheffield, J., Reichstein, M. and Seneviratne, S.I. 2014. Global assessment of trends in wetting and drying over land. Nature Geoscience 7: 716-721.

Sheffield, J., Wood, E.F. and Roderick, M.L. 2012. Little change in global drought over the past 60 years. Nature 491: 435-438.

Posted 31 August 2015