Beyond Linear Scaling: Dynamical Controls on European Precipitation Extremes

Abstract. This study investigates the scalability of extreme precipitation indices across the Mediterranean Basin and Europe using 0.11° EURO-CORDEX regional climate model projections. A pattern-scaling framework is applied to assess whether changes in extreme precipitation exhibit a robust relationship with increments in global mean temperature and to determine the time of emergence of scalable patterns during the twenty-first century. Scaling relationships are derived for five extreme precipitation indices using annual mean global temperature change from the driving global climate models.

A clear distinction emerges between ensemble-mean behavior and individual model responses. For most indices, the ensemble mean converges toward the late-century pattern relatively early in the century, suggesting that large-scale thermodynamic control linked to global warming governs the forced signal in precipitation extremes. Individual model realizations, however, display substantially greater spread and often lack a stable scaling relationship until much later in the century.

Projected changes reveal a pronounced north–south contrast across Europe, with increasing precipitation extremes in northern regions and progressively drier conditions across much of the Mediterranean Basin and southern Europe. However, the analysis shows that precipitation extremes do not conform uniformly to a linear scaling with global mean temperature. In contrast to temperature-based metrics, a robust linear relationship for precipitation emerges only gradually and remains weak or absent for the most extreme indices.

Crucially, the breakdown of linear scaling is not merely a limitation of the framework, but a physically informative signal indicating a transition in the controlling mechanisms of precipitation extremes. The forced thermodynamic response becomes clearly distinguishable from internal variability by around mid-century, but for the most extreme events, the deviation from scalable behavior reflects an increasing dominance of regional circulation changes and large-scale dynamical adjustments over thermodynamic constraints alone. In this regime, departures from scaling capture the growing influence of atmospheric dynamics rather than uncertainty.

By the late century, projected changes in several indices remain broadly consistent with large-scale patterns of change, yet the least scalable metrics highlight where dynamical processes override temperature-driven expectations. As a result, some precipitation metrics can be linked to warming more directly than others. This distinction has important implications for pattern-scaled projections, as the breakdown of scaling provides insight into when and where atmospheric dynamics become the primary control on European precipitation extremes, rather than representing noise around a simple thermodynamic response.