Redistribution of frost weathering across Spain under recent climate warming

Abstract. Frost weathering (cryoclasty) is a key cryospheric process controlling rock breakdown, sediment production, and the mechanical evolution of landscapes at mid- to high latitudes. Its effectiveness depends on the interaction between temperature variability, moisture availability, and the frequency of freeze–thaw transitions. Here we analyse the spatial and temporal dynamics of frost activity across Spain during 1993–2022 using daily temperature and precipitation records from 84 meteorological stations spanning alpine, oceanic, inland Mediterranean, coastal, and subtropical environments. Five cryoclimatic indicators were evaluated to characterise both thermal severity and hydro-thermal effectiveness: Frost Days (FD), Freeze–Thaw Cycles (FTC), Intense Freeze–Thaw Cycles (IFTC), the Frost Intensity Index (FI), and the Wet-Frost Index (WFI).

Results reveal a strong concentration of effective frost weathering in mountainous and perimountainous regions, while frost activity is marginal or absent in lowland Mediterranean, coastal, and subtropical areas. Over the last three decades, most of Spain shows a statistically significant decline in frost days and freeze–thaw cycles, accompanied by a shortening of the frost season. In contrast, perimountainous belts exhibit sustained or locally increasing frost intensity and frequent transitions through the frost-cracking temperature window. The Wet-Frost Index highlights a progressive spatial contraction of moisture-effective frost conditions, with linear projections to 2050 suggesting that effective frost weathering will become increasingly restricted to high-altitude mountain environments. These findings show that climate warming is redistributing, rather than uniformly suppressing, frost-driven cryospheric processes at the southern margins of Europe.