Hydroclimate variability in Scandinavia over the last millennium – insights from a climate model–proxy data comparison

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 GCMsimulated 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.

European warm-season temperature and hydroclimate since 850 CE

“…Increasing evidence suggests that the model-based paradigm of 'wet-gets-wetter and dry-gets-drier' in a warmer world (Trenberth et al 2003, Held andSoden 2006) may be too simplistic (Sheffield et al 2012, Greve et al 2014, Byrne and O'Gorman 2015, Burls and Fedorov 2017. At the same time, evidence for a timescale-dependence of temperature-hydroclimate relationships is emerging (Rehfeld and Laepple 2016), but instrumental observations are too short to derive robust co-variations at longer timescales (Seftigen et al 2017). The elusive key to clarifying these relationships lies in understanding how temperature relates to precipitation, evapotranspiration and drought on multiple spatiotemporal scales.…”

“…The Mediterranean Basin displays timescale-dependent and spatially diverse hydroclimate patterns throughout the past millennium, manifested by an east-west dipole at annual to decadal scales (Xoplaki et al 2004, Roberts et al 2012, Seim et al 2015, Labuhn et al 2018, Jones et al 2019, which disappears on multi-decadal to centennial timescales (Cook et al 2016). Distinct hydroclimatic dipole patterns in Europe, lasting several years, also follow large volcanic eruptions, with humid conditions in northeastern Europe, and drier conditions in northwestern Europe and parts of the Mediterranean (Fischer et al 2007, Büntgen et al 2017, Gao and Gao 2017, Rao et al 2017, Xoplaki et al 2018, Schurer et al 2019.…”

“…The biological memory of climate conditions from the previous year(s), affecting the annual increments of tree growth, can potentially lead to an overestimation of low-frequency signals if not treated properly(Esper et al 2015).Although the OWDA hydroclimate reconstruction allows for a highly skillful assessment of past drought variability in time and space(Cook et al 2016, Markonis et al 2018, Marvel et al 2019, it may still contain biases affecting the assessed co-variance with (reconstructed) temperature variability. The observed positive deviation (relative to instrumental data) in the tree-ring reconstructed temperature-hydroclimate relationship is likely the result of tree growth being influenced by both temperature and precipitation(Babst et al 2013, Seftigen et al 2017, Klesse et al 2018…”

Two millennia of Main region (southern Germany) hydroclimate variability

“…An attempt of such can be found in Land et al (2015) and Schönbein et al (2015). Nevertheless, single seasons with pronounced below-average (e.g., AD 338)/above-average (e.g., AD 357) average rainfall totals as well as very dry several-year periods (e.g., around AD 1395) appeared in the MR. Interestingly, Spurk et al (2002) investigated the depositional frequency of subfossil oaks in the MR, which includes the tree samples used here, and linked them to climatically induced fluctuations. They found a sudden onset of germination at AD 400 in the MR, indicating humid conditions.…”

“…Changes in air temperature have been intensively investigated with temperature-sensitive tree-ring chronologies (here, we refer to Wilson et al, 2016;Anchukaitis et al, 2017 and references therein) on a regional to global scale. A comparable number of studies have also investigated long-term (century to millennia) hydroclimate variability, rainfall and drought intensity (e.g., Hughes and Brown, 1992;Esper et al, 2007;Cook et al, 2004Cook et al, , 2007Cook et al, , 2015Stockton and Meko, 1975;Ljungqvist et al, 2016;Prokop et al, 2016;Cooper et al, 2013;Wilson et al, 2005Wilson et al, , 2013; Levanič et al, 2013;Ruiz-Labourdette et al, 2014;Seftigen et al, 2017;Helama et al, 2009;Kress et al, 2014). For continental Europe, only a small number of tree-ring hydroclimate reconstructions exist which cover the entire Common Era, and very few studies address the challenge of investigation hydroclimate fluctuations before Common Era Büntgen et al, 2011;Pechtl and Land, 2019;Schönbein et al, 2015).…”