Land surface and atmosphere are interlocked by the hydrological and energy cycles and the effects of soil water-air coupling can modulate near-surface temperatures. In this work, three paired experiments were designed to evaluate impacts of different soil moisture initial and boundary conditions on summer temperatures in the Mediterranean transitional climate regime region. In this area, evapotranspiration is not limited by solar radiation, rather by soil moisture, which therefore controls the boundary layer variability. Extremely dry, extremely wet and averagely humid ground conditions are imposed to two global climate models at the beginning of the warm and dry season. Then, sensitivity experiments, where atmosphere is alternatively interactive with and forced by land surface, are launched. The initial soil state largely affects summer near-surface temperatures: dry soils contribute to warm the lower atmosphere and exacerbate heat extremes, while wet terrains suppress thermal peaks, and both effects last for several months. Land-atmosphere coupling proves to be a fundamental ingredient to modulate the boundary layer state, through the partition between latent and sensible heat fluxes. In the coupled runs, early season heat waves are sustained by interactive dry soils, which respond to hot weather conditions with increased evaporative demand, resulting in longer-lasting extreme temperatures. On the other hand, when wet conditions are prescribed across the season, the occurrence of hot days is suppressed. The land surface prescribed by climatological precipitation forcing causes a temperature drop throughout the months, due to sustained evaporation of surface soil water. Results have implications for seasonal forecasts on both rain-fed and irrigated continental regions in transitional climate zones.

地表和大气通过水文和能量循环相互关联，土壤水-空气耦合的影响可以调节近地表温度。在这项工作中，设计了三个配对实验来评估不同土壤湿度初始和边界条件对地中海过渡气候区夏季温度的影响。在该地区，蒸散不受太阳辐射的限制，而是受土壤湿度的限制，因此控制了边界层的变化。在暖季和旱季开始时，极端干燥、极端潮湿和平均潮湿的地面条件被强加给两个全球气候模型。然后，启动大气与地表交互作用和受地表强迫的敏感性实验。初始土壤状态在很大程度上影响夏季近地表温度：干燥的土壤使低层大气变暖并加剧极端高温，而潮湿的地形抑制了热峰值，这两种影响都会持续数月。陆地-大气耦合被证明是通过潜热通量和显热通量之间的划分来调节边界层状态的基本要素。在耦合运行中，早期的热浪是由相互作用的干燥土壤维持的，这些土壤通过增加蒸发需求来应对炎热的天气条件，从而导致持续时间更长的极端温度。另一方面，当整个季节规定潮湿条件时，可抑制炎热天气的出现。气候降水强迫规定的地表导致整个月份的温度下降，由于地表土壤水分的持续蒸发。结果对过渡气候区的雨养和灌溉大陆地区的季节性预报有影响。