Groundwater-driven land subsidence as an emerging risk to historical monuments in central Germany

Climate change is altering the dynamics of groundwater fluctuations and posing new challenges for groundwater management worldwide. The decline in winter snow cover shifts precipitation infiltration more toward the winter season, while a prolonged vegetation period enhances evapotranspiration, leading to greater summer groundwater depletion. Extreme weather events such as floods and droughts, together with increasing water extraction driven by rising water demand, promote repeated cycles of drying and rewetting in near-surface, unconsolidated sediments. Over time, these cycles alter the hydromechanical properties of the subsoil and increase its susceptibility to deformation and subsidence.

In this study, we investigate these subsidence and deformation processes at historical monuments in central Germany, which have experienced pronounced structural damage. Since 2024, five observation sites of historic churches in the federal states of Saxony and Saxony-Anhalt have been monitored. These sites were selected because they are predominantly located in rural regions, where groundwater systems are comparatively less affected by urban-related stressors, allowing climate-related groundwater fluctuations to be examined with reduced interference from superimposed anthropogenic signals. The monuments were constructed several centuries ago and have remained largely stable over time. However, after several years of extreme weather conditions, significant cracks began to appear around 2016. In some cases, the buildings were temporarily classified as being at risk of collapse. Since the damage did not occur immediately following individual extreme events but developed over an extended period, the long-term trend in subsurface water saturation needs to be investigated. To distinguish persistent drying trends from seasonal fluctuations, quarterly electrical resistivity tomography (ERT) measurements were conducted in the vicinity of the monuments along fixed profiles with lengths of up to 160 m during six field campaigns between April 2024 and November 2025. During the observation period, the electrical resistivity in the shallow subsurface increased significantly, indicating progressive desiccation to a depth of approximately 5 m, with wintertime rewetting insufficient to restore moisture levels. This prolonged desiccation likely induced further shrinkage and deformation, especially in the clay-rich layers. In contrast, a decrease in electrical resistivity was measured in the deeper layers, indicating a higher moisture content compared to the drier upper soil layers. Continued monitoring will further contribute to determining the long-term effects of climate variability on subsurface moisture dynamics, delineating zones with critical moisture changes, and linking these to settlement-prone areas of the monuments.