The 1820s Marks a Shift to Hotter‐Drier Summers in Western Europe Since 13

Abstract

    Soil moisture is the primary indicator for assessing agricultural and ecological drought, and its relationship with temperature has a great impact on regional climates, such as triggering heat waves. So far, studies on the coupling relationship between soil moisture and temperature have mainly focused on arid or semi-arid regions with strong land-atmosphere coupling. However, less attention has been paid to humid regions with relatively weak coupling between soil moisture and temperature there. In recent years, a number of studies have found that heat waves in humid regions are directly related to the coupling of soil moisture and temperature. Nevertheless, historical changes of soil moisture and its relationship with temperature in humid areas are still unclear.    In this study, three sampling sites with published long-term tree ring δ18O records in England and France were selected to reconstruct the surface (0–10 cm) soil moisture changes in Western Europe (40°N–55°N, 10°W–10°E) from 1360 to 2000 AD. Various abrupt-change detecting tests (Mann-Kendall test, Yamamoto method, and Bernaola-Galvan segmentation algorithm) showed that soil moisture began to decline suddenly around 1820, with increasing dry years and decreasing wet years, and no wet years after 1950 . After 1820, the coupling of soil moisture and temperature was growing stronger than before. Compared with the historical period, the summer sea level pressure anomaly is stronger in the dry years after 1820, which may be related to the weakened westerly circulation and water vapor transport. These findings suggest that, in the context of global warming, hotter and drier conditions are occurring not only in arid regions, but also in humid western Europe. Under future warming scenarios, humid regions may also be threatened by hot droughts.