Varying soil moisture–atmosphere feedbacks explain divergent temperature extremes and precipitation projections in central Europe

Abstract

Abstract. The frequency and intensity of climate extremes is expected to increase in many regions due to anthropogenic climate change. In central Europe extreme temperatures are projected to change more strongly than global mean temperatures, and soil moisture–temperature feedbacks significantly contribute to this regional amplification. Because of their strong societal, ecological and economic impacts, robust projections of temperature extremes are needed. Unfortunately, in current model projections, temperature extremes in central Europe are prone to large uncertainties. In order to understand and potentially reduce the uncertainties of extreme temperature projections in Europe, we analyze global climate models from the CMIP5 (Coupled Model Intercomparison Project Phase 5) ensemble for the business-as-usual high-emission scenario (RCP8.5). We find a divergent behavior in long-term projections of summer precipitation until the end of the 21st century, resulting in a trimodal distribution of precipitation (wet, dry and very dry). All model groups show distinct characteristics for the summer latent heat flux, top soil moisture and temperatures on the hottest day of the year (TXx), whereas for net radiation and large-scale circulation no clear trimodal behavior is detectable. This suggests that different land–atmosphere coupling strengths may be able to explain the uncertainties in temperature extremes. Constraining the full model ensemble with observed present-day correlations between summer precipitation and TXx excludes most of the very dry and dry models. In particular, the very dry models tend to overestimate the negative coupling between precipitation and TXx, resulting in a warming that is too strong. This is particularly relevant for global warming levels above 2 ∘C. For the first time, this analysis allows for the substantial reduction of uncertainties in the projected changes of TXx in global climate models. Our results suggest that long-term temperature changes in TXx in central Europe are about 20 % lower than those projected by the multi-model median of the full ensemble. In addition, mean summer precipitation is found to be more likely to stay close to present-day levels. These results are highly relevant for improving estimates of regional climate-change impacts including heat stress, water supply and crop failure for central Europe.

Regional climate model projections underestimate future warming due to missing plant physiological CO2 response

“…Consequently, the estimated ET reductions in central Europe strongly depend on the choice of GCMs considered in the GCM-RCM model chains. This large uncertainty in the estimated ET reductions in central Europe is likely connected to the divergent ET trend projections by GCMs in this region (Vogel et al 2018). In contrast, the different ET reduction estimates agree well in northern and southern Europe, which gives confidence in the robustness of the estimated plant physiological effect on ET in these regions.…”

“…While the ET reductions in northern and southern Europe caused by stomatal adaptation are robust across models, the effects in central Europe are more uncertain, ranging from small to potentially very large ET decreases (figure 2). The high uncertainty stems from ET reductions being very sensitive to the selection of GCMs in central Europe and thus mainly reflects the divergent ET trend projections by GCMs in this region (Vogel et al 2018).…”

Half‐a‐Degree Matters for Reducing and Delaying Global Land Exposure to Combined Daytime‐Nighttime Hot Extremes

“…When projected results are used for decision-making, the uncertainty range sourced from intermember (Figure 5a shadings)/intermodel (Figures 2 and 3 shadings) spreads should be kept in mind and communicated explicitly. Increasingly available global-scale daily observations and growing maturation of observation-constrained techniques are promising to help reduce uncertainties of projected changes of extremes (Borodina et al, 2017;Vogel et al, 2018).…”

The drivers of nonlinear local temperature change under global warming

“…In moisture-limited regions, including continental Europe (Fischer et al 2007, Vogel et al 2018 and north-eastern Australia (Nicholls 2004, King et al 2014a, there is a strong inverse relationship between summertime precipitation and temperature indices. Indeed, in Europe this has been used to attempt to constrain model projections (Vogel et al 2018) and a similar approach is undertaken here, whereby the most accurate models for observed summer precipitation-temperature (P-T) relationships are selected ( figure 4(b), supplementary table S2) and projections are produced. This approach tends to remove the models with the stronger nonlinearities in temperature projections ( figure 4(b)).…”