Assessing the Feasibility of Satellite‐Based Thresholds for Hydrologically Driven Landsliding. Issue 11 (13th November 2019)

• Record Type: Journal Article
• Authors: Thomas, Matthew A.; Collins, Brian D.; Mirus, Benjamin B.
• Is Part Of: Water resources research. Volume 55:Issue 11(2019)
• Page Start: 9006
• Page End: 9023
• Publication Date: 2019-11-13
• Subjects: hillslope hydrology -- in situ monitoring -- remote sensing -- landslides -- thresholds; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2019WR025577
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Elevated soil moisture and heavy precipitation contribute to landslides worldwide. These environmental variables are now being resolved with satellites at spatiotemporal scales that could offer new perspectives on the development of landslide warning systems. However, the application of these data to hydrometeorological thresholds (which account for antecedent soil moisture and rainfall) first needs to be evaluated with respect to proven, direct measurement‐based thresholds that use rain gages and in situ soil moisture sensors. Here we compare ground‐based hydrologic data to overlapping satellite‐based data before, during, and after a recent season of widespread shallow landsliding in the San Francisco Bay Area (California, USA). We then explore how the remotely sensed information could be used to empirically define hypothetical thresholds for shallow landsliding. We find that the ground‐based thresholds developed with a single monitoring station show superior performance because the in situ soil saturation data better reflect the gravity‐dominated subsurface flow conditions that are characteristic of hillslopes during the rainy season. Although the satellite‐based thresholds can identify most of the landslide days, they include a greater number of false alarms due to overestimates of soil moisture between major storm events. To avoid the type of false alarms that are characteristic of our satellite‐based thresholds, further postprocessing of the near‐surface hydrologic response data should be integrated into satellite‐based model outputs to better reflect gravity‐dominated drainage. Our results encourage further deployment of ground stations in landslide‐prone terrain and cautious exploration of satellite‐based hydrometeorological thresholds where in situ networks are nonexistent. Plain Language Summary: Soil wetness and rainfall contribute to landslides across the world. Using soil moisture sensors and rain gages, these environmental conditions have been monitored at numerous points across the Earth's surface to define threshold conditions, above which landsliding should be expected for a localized area. Satellite‐based technologies also deliver estimates of soil wetness and rainfall, potentially offering an approach to develop thresholds as part of landslide warning systems over larger spatial scales. To evaluate the potential for using satellite‐based measurements for landslide warning, we compare the accuracy of landslide thresholds defined with ground‐ versus satellite‐based soil wetness and rainfall information. We find that the satellite‐based data overpredict soil wetness during the time of year when landslides are most likely to occur, resulting in thresholds that also overpredict the potential for landslides relative to thresholds informed by direct measurements on the ground. Our results encourage the installation of more ground‐based monitoring stations in landslide‐prone settings and the cautious use of satellite‐based data when more direct measurements are not available. Key Points: We compared hydrometeorological thresholds for landslide initiation defined with ground‐ versus satellite‐based information Ground‐based thresholds show superior performance because in situ soil moisture data better reflect gravity‐dominated subsurface flow Satellite‐based thresholds produce more false alarms but may merit consideration where in situ soil moisture data are nonexistent