TUM - Technical University of Munich, Arcisstraße 21, 80333 Munich, Germany.
TUM - Technical University of Munich, Arcisstraße 21, 80333 Munich, Germany.
Sci Total Environ. 2022 Mar 1;810:152193. doi: 10.1016/j.scitotenv.2021.152193. Epub 2021 Dec 7.
Shallow aquifers beneath cities are highly influenced by anthropogenic heat sources, resulting in the formation of extensive subsurface urban heat islands. In addition to anthropogenic factors, natural factors also influence the subsurface temperature. However, the effect of individual factors is difficult to capture due to high temporal dynamics in urban environments. Particularly in the case of shallow aquifers, seasonal temperature fluctuations often override the influence of existing heat sources or sinks. For the city of Munich, we identify the dominant anthropogenic and natural influences on groundwater temperature and analyse how the influences change with increasing depth in the subsurface. For this purpose, we use depth temperature profiles from 752 selected groundwater monitoring wells. Since the measurements were taken at different times, we developed a statistical approach to compensate for the different seasonal temperature influences using passive heat tracing. Further, we propose an indicator to spatially assess the thermal stress on the aquifer. A multiple regression analysis of four natural and nine anthropogenic factors identified surface sealing as the strongest and the district heating grid as a weak but significant warming influence. The natural factors, aquifer thickness, depth-to-water and Darcy velocity show a significant cooling influence on the groundwater temperature. In addition, we show that local drivers, like thermal groundwater uses, surface waters and underground structures do not significantly contribute to the city-wide temperature distribution. The subsequent depth-dependent analysis revealed that the influence of aquifer thickness and depth-to-water increases with depth, whereas the influence of Darcy velocity decreases, and surface sealing and the heating grid remain relatively constant. In conclusion, this study shows that the most critical factor for the mitigation of future groundwater warming in cities is to minimize further sealing of the ground, to restore the permeability of heavily sealed areas and to retain open landscapes.
城市浅层含水层受人为热源影响较大，导致广泛的地下城市热岛的形成。除人为因素外，自然因素也会影响地下温度。然而，由于城市环境的时间动态变化很大，个别因素的影响很难捕捉。特别是在浅层含水层的情况下，季节性温度波动常常会超过现有热源或汇的影响。以慕尼黑市为例，我们确定了对地下水温度有影响的主要人为因素和自然因素，并分析了这些影响随着地下深度的增加而如何变化。为此，我们使用了 752 个选定的地下水监测井的深度温度剖面。由于测量是在不同的时间进行的，我们开发了一种统计方法，使用被动热示踪来补偿不同季节温度的影响。此外，我们提出了一个指标来对含水层的热应力进行空间评估。对四个自然因素和九个人为因素进行的多元回归分析确定了地表密封是最强的影响因素，而区域供热网是较弱但显著的增温影响因素。自然因素，含水层厚度、水深和达西速度对地下水温度有显著的冷却影响。此外，我们还表明，局部驱动因素，如热地下水利用、地表水和地下结构，并没有对全市的温度分布产生显著影响。随后的深度相关分析表明，含水层厚度和水深的影响随深度增加而增加，而达西速度的影响则减小，地表密封和供热网的影响则相对稳定。总之，本研究表明，在城市中减缓未来地下水升温的最关键因素是尽量减少地面的进一步密封，恢复重度密封区域的渗透性，并保留开放的景观。
