Understanding the relationship between the water crisis and sustainability of the Angkor World Heritage site

The sustainability of Angkor World Heritage site (Cambodia) has been of increasing concern due to rapid socioeconomic development of the surrounding region including the booming city of Siem Reap. We interpret findings from satellite radar interferometry (InSAR) motion fields for the period 2007-2017 to derive new insights into the dynamics of the relationship between land subsidence, groundwater extraction and monument stability. Evolution of motion trends along with hydraulic heads indicated that the surface in the archaeological zone was stable up to 2011, followed by a mild subsidence during 2011-2017, primarily impacted by unregulated tourism development. Spatially decline of groundwater table beneath Siem Reap City could, in the future, threaten the stability of monuments. We developed a model that predicted that surface subsidence in the central archaeological zone could reach up to -3.6 to -3.8 mm/yr by 2021 if a 6% annual increase of tourists and the resulting demand for groundwater resources continued. A tourism carrying capacity below 2.5 million per year may be sustainable to prevent the emergence of hydrological problems that could exacerbate the risk of significant land subsidence and consequences for monument stability. This study is a clear illustration of the value of InSAR space-eye combined with ground-based measurements for monitoring potential hazards and modelling conservation states of World Heritage sites in order to improve preparedness critical for mitigating future threats.