Abstract
Abstract. The integration of climate proxy information with general circulation model (GCM) results offers considerable potential for deriving greater understanding of the mechanisms underlying climate variability, as well as unique opportunities for out-of-sample evaluations of model performance. In this study, we combine insights from a new tree-ring hydroclimate reconstruction from Scandinavia with projections from a suite of forced transient simulations of the last millennium and historical intervals from the CMIP5 and PMIP3 archives. Model simulations and proxy reconstruction data are found to broadly agree on the modes of atmospheric variability that produce droughts–pluvials in the region. Despite these dynamical similarities, large differences between simulated and reconstructed hydroclimate time series remain. We find that the GCM-simulated multi-decadal and/or longer hydroclimate variability is systematically smaller than the proxy-based estimates, whereas the dominance of GCM-simulated high-frequency components of variability is not reflected in the proxy record. Furthermore, the paleoclimate evidence indicates in-phase coherencies between regional hydroclimate and temperature on decadal timescales, i.e., sustained wet periods have often been concurrent with warm periods and vice versa. The CMIP5–PMIP3 archive suggests, however, out-of-phase coherencies between the two variables in the last millennium. The lack of adequate understanding of mechanisms linking temperature and moisture supply on longer timescales has serious implications for attribution and prediction of regional hydroclimate changes. Our findings stress the need for further paleoclimate data–model intercomparison efforts to expand our understanding of the dynamics of hydroclimate variability and change, to enhance our ability to evaluate climate models, and to provide a more comprehensive view of future drought and pluvial risks.
Highlights
Among the current key priorities in climate research is a more comprehensive understanding of changes in regionalto continental-scale hydroclimate in response to rising levels of atmospheric greenhouse gases on timescales ranging from decades to centuries (Wu et al, 2013; Hegerl et al, 2015)
The regional warm-season hydroclimate variability averaged across the six CMIP5–PMIP3 models together with the new ScandH17 proxy reconstruction over the last millennium are shown in Fig. 2a and b
This study presents the first comprehensive assessment of past variability and trends in hydroclimate of the northern European sector over the last millennium of the Common Era along with interrelated variables: precipitation, which supplies moisture, and temperature, which modulates evapotranspiration
Summary
Among the current key priorities in climate research is a more comprehensive understanding of changes in regionalto continental-scale hydroclimate in response to rising levels of atmospheric greenhouse gases on timescales ranging from decades to centuries (Wu et al, 2013; Hegerl et al, 2015). The longest instrumental records ( ∼ 150–200 years) are too short to fully sample modes of variability that are either rare or occur on multi-decadal to centennial timescales This motivates the development of paleoclimatic proxy reconstructions, which extends the observational baseline into the longer spectrum of climate variability and provides a framework to consider both internal and forced climate changes. Much of the tree-ring research at moisture-limited sites has until recently been limited to a handful of exploratory papers (Helama and Lindholm, 2003; Linderholm et al, 2004; Jönsson and Nilsson, 2009; Drobyshev et al, 2011; Seftigen et al, 2013) that generally develop one or a few chronologies to provide local precipitation and drought histories.
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