European warm-season temperature and hydroclimate since 850 CE

Fredrik Charpentier Ljungqvist,Edward R Cook,Mary H Gagen,Elena García-Bustamante,Paul J Krusic,Andrea Seim,Jürg Luterbacher,Elena Xoplaki,Georgia Destouni,Olga Solomina,Ulf Büntgen,Jan Esper,Jesús Fidel González-Rouco,Johannes P Werner,Eduardo Zorita,Jianglin Wang,Camilo Andrés Melo Aguilar,Kristina Seftigen,Dominik Fleitmann

doi:10.1088/1748-9326/ab2c7e

Abstract

The long-term relationship between temperature and hydroclimate has remained uncertain due to the short length of instrumental measurements and inconsistent results from climate model simulations. This lack of understanding is particularly critical with regard to projected drought and flood risks. Here we assess warm-season co-variability patterns between temperature and hydroclimate over Europe back to 850 CE using instrumental measurements, tree-ring based reconstructions, and climate model simulations. We find that the temperature–hydroclimate relationship in both the instrumental and reconstructed data turns more positive at lower frequencies, but less so in model simulations, with a dipole emerging between positive (warm and wet) and negative (warm and dry) associations in northern and southern Europe, respectively. Compared to instrumental data, models reveal a more negative co-variability across all timescales, while reconstructions exhibit a more positive co-variability. Despite the observed differences in the temperature–hydroclimate co-variability patterns in instrumental, reconstructed and model simulated data, we find that all data types share relatively similar phase-relationships between temperature and hydroclimate, indicating the common influence of external forcing. The co-variability between temperature and soil moisture in the model simulations is overestimated, implying a possible overestimation of temperature-driven future drought risks.

Highlights

The value at each grid-cell, e.g. self-calibrating Palmer Drought Severity Index (scPDSI), represents the average value of that grid-cell: re-gridding to a coarser grid was performed by averaging the values at all gridcells of the finer grids that lie within a particular gridcell of the coarser grid
The instrumental period We find significant negative correlations between 20 year high-passed filtered summer (June–August) instrumental temperature and scPDSI data over Europe for the period 1901–2003
A similar negative relationship is observed between high-pass filtered instrumental June–August temperature and precipitation as well as between March–August temperature and scPDSI or precipitation

Summary

Introduction

Duration, and severity of either droughts or floods are expected to accompany global warming in many parts of the world, posing threats to the environment and societies alike (D’Odorico and Bhattachan 2012, Field et al 2014, Schewe et al 2014, van Loon et al 2016, Lehner et al 2017, Orth and Destouni 2018, Trnka et al 2018). The development of strategies for long-term climate change mitigation are hampered by inconsistent climate model projections of future hydroclimatic changes at regional scales (Stephens et al 2010, Christensen et al 2013, Orlowsky and Seneviratne 2013, Nasrollahi et al 2015). 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 and Soden 2006) may be too simplistic (Sheffield et al 2012, Greve et al 2014, Byrne and O’Gorman 2015, Burls and Fedorov 2017). 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). Model simulations tend to underestimate the natural long-term hydroclimatic variability and to overestimate the amplitude of twentieth century changes relative to past variations (Ljungqvist et al 2016)

Methods

Results

Discussion

Conclusion