Abstract. An assessment of the soil and bedrock thermal structure of the Sierra de Guadarrama, in Central Spain, is provided using subsurface and ground surface temperature data coming from four deep (20 m) monitoring profiles belonging to the Guadarrama Monitoring Network (GuMNet), and two shallow (1 m) from the Spanish Meteorology Service (AEMET), covering the time span of 2015–2021 and 1989–2018, respectively. An evaluation of air and ground surface temperature coupling shows soil insulation due to snow cover is the main source of seasonal decoupling, being especially relevant in winter at high altitude sites. Temperature propagation in the subsurface is characterized by assuming a heat conductive regime, by considering apparent thermal diffusivity values derived from the amplitude attenuation and phase shift of the annual cycle with depth. For the deep profiles, the apparent thermal diffusivity ranges from 1 to 1.3 10⁻⁶ m²s⁻¹, consistent with values for gneiss and granite, the major bedrock components in the Sierra de Guadarrama. However, thermal diffusivity is lower and more heterogeneous in the soil layers close to the surface (0.4–0.8 10⁻⁶ m²s⁻¹). An increase of diffusivity with depth is observed, being generally larger in the soil-bedrock transition, at 4–8 m depth. A new method based on the spectral attenuation of temperature harmonics allows for analyzing thermal diffusivity from high-frequency changes in the soil near the surface at short timescales. The results are relevant for the understanding of soil thermodynamics in relation to other soil properties and suggest that changes in heat diffusivity are related to soil moisture content changes, which makes this method a potential tool in soil drought and water resource availability reconstruction from soil temperature data.

中文翻译：

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西班牙中部地下热状态的热力学和水文驱动因素

摘要。使用来自属于瓜达拉马监测网络 (GuMNet) 的四个深度 (20 m) 监测剖面的地下和地表温度数据，以及两个来自西班牙气象局（AEMET）的浅层（1 m），分别涵盖 2015-2021 年和 1989-2018 年的时间跨度。对空气和地表温度耦合的评估表明，积雪造成的土壤绝缘是季节性脱钩的主要来源，尤其是在高海拔地区的冬季。地下温度传播的特征是假设导热状态，通过考虑从年循环随深度的振幅衰减和相移得出的表观热扩散率值。⁻⁶ m ² s ⁻¹，与片麻岩和花岗岩的值一致，这是 Sierra de Guadarrama 的主要基岩成分。然而，在靠近地表的土壤层中，热扩散系数较低且更不均匀 (0.4–0.8 10 ^-6 m ² s ^-1). 观察到扩散率随深度增加，在 4-8 m 深度的土壤-基岩过渡中通常较大。一种基于温度谐波光谱衰减的新方法可以分析短时间内地表附近土壤高频变化的热扩散率。该结果对于理解与其他土壤特性相关的土壤热力学相关，并表明热扩散率的变化与土壤水分含量的变化有关，这使得该方法成为根据土壤温度数据重建土壤干旱和水资源可用性的潜在工具.