Integrating real-time subsurface hydrologic monitoring with empirical rainfall thresholds to improve landslide early warning

Early warning for rainfall-induced shallow landsliding can help reduce fatalities and economic losses. Although these commonly occurring landslides are typically triggered by subsurface hydrological processes, most early warning criteria rely exclusively on empirical rainfall thresholds and other indirect proxies for subsurface wetness. We explore the utility of explicitly accounting for antecedent wetness by integrating real-time subsurface hydrologic measurements into landslide early warning criteria. Our efforts build on previous progress with rainfall thresholds, monitoring, and numerical modeling along the landslide-prone railway corridor between Everett and Seattle, Washington, USA. We propose a modification to a previously established recent versus antecedent (RA) cumulative rainfall thresholds by replacing the antecedent 15-day rainfall component with an average saturation observed over the same timeframe. We calculate this antecedent saturation with real-time telemetered measurements from five volumetric water content probes installed in the shallow subsurface within a steep vegetated hillslope. Our hybrid rainfall versus saturation (RS) threshold still relies on the same recent 3-day rainfall component as the existing RA thresholds, to facilitate ready integration with quantitative precipitation forecasts. During the 2015–2017 monitoring period, this RS hybrid approach has an increase of true positives and a decrease of false positives and false negatives relative to the previous RA rainfall-only thresholds. We also demonstrate that alternative hybrid threshold formats could be even more accurate, which suggests that further development and testing during future landslide seasons is needed. The positive results confirm that accounting for antecedent wetness conditions with direct subsurface hydrologic measurements can improve thresholds for alert systems and early warning of rainfall-induced shallow landsliding.

[1]  Konstantine P. Georgakakos,et al.  Soil moisture and precipitation thresholds for real-time landslide prediction in El Salvador , 2015, Landslides.

[2]  Thom Bogaard,et al.  Landslide hydrology: from hydrology to pore pressure , 2016 .

[3]  Rex L. Baum,et al.  Rainfall characteristics for shallow landsliding in Seattle, Washington, USA , 2006 .

[4]  M. Rossi,et al.  The rainfall intensity–duration control of shallow landslides and debris flows: an update , 2008 .

[5]  Matthias Jakob,et al.  A regional real-time debris-flow warning system for the District of North Vancouver, Canada , 2012, Landslides.

[6]  B. Collins,et al.  STABILITY ANALYSES OF RAINFALL INDUCED LANDSLIDES , 2004 .

[7]  J. Moody,et al.  Hyper-dry conditions provide new insights into the cause of extreme floods after wildfire , 2012 .

[8]  J. Godt,et al.  Early warning of rainfall-induced shallow landslides and debris flows in the USA , 2010 .

[9]  N. Caine,et al.  The Rainfall Intensity - Duration Control of Shallow Landslides and Debris Flows , 1980 .

[10]  R. Greco,et al.  Invited perspectives: Hydrological perspectives on precipitation intensity-duration thresholds for landslide initiation: proposing hydro-meteorological thresholds , 2017 .

[11]  Luca Brocca,et al.  On the estimation of antecedent wetness conditions in rainfall–runoff modelling , 2008 .

[12]  Thomas Glade,et al.  Climatic factors influencing occurrence of debris flows , 2005 .

[13]  Rex L. Baum,et al.  Transient deterministic shallow landslide modeling: Requirements for susceptibility and hazard assessments in a GIS framework , 2008 .

[14]  Rex L. Baum,et al.  A prototype system for forecasting landslides in the Seattle, Washington, area , 2008 .

[15]  J. Schaefer.  The critical success index as an indicator of Warning skill , 1990 .

[16]  R. Baum,et al.  Hydrologic Impacts of Landslide Disturbances: Implications for Remobilization and Hazard Persistence , 2017 .

[17]  Rex L. Baum,et al.  Precipitation thresholds for landslide occurrence near Seattle, Mukilteo, and Everett, Washington , 2017 .

[18]  W. M. Brown,et al.  Real-Time Landslide Warning During Heavy Rainfall , 1987, Science.

[19]  M. Rossi,et al.  Do landslides follow landslides? Insights in path dependency from a multi-temporal landslide inventory , 2017, Landslides.

[20]  Graziella Devoli,et al.  Adapting the EDuMaP method to test the performance of the Norwegian early warning system for weather-induced landslides , 2017 .

[21]  Jason W. Kean,et al.  Objective definition of rainfall intensity–duration thresholds for the initiation of post-fire debris flows in southern California , 2013, Landslides.

[22]  Jonathan P. McKenna,et al.  Hydrologic monitoring of landslide-prone coastal bluffs near Edmonds and Everett, Washington, 2001-2004 , 2005 .

[23]  R. Baum,et al.  Assessing landslide potential on coastal bluffs near Mukilteo, Washington—Geologic site characterization for hydrologic monitoring , 2016 .

[24]  J. Godt,et al.  Effect of antecedent-hydrological conditions on rainfall triggering of debris flows in ash-fall pyroclastic mantled slopes of Campania (southern Italy) , 2016, Landslides.

[25]  R. Sidle,et al.  Landslides: Processes, Prediction, and Land Use , 2006 .

[26]  Davide Tiranti,et al.  Estimation of rainfall thresholds triggering shallow landslides for an operational warning system implementation , 2010 .

[27]  R. Greco,et al.  Is there Predictive Power in Hydrological Catchment Information for Regional Landslide Hazard Assessment , 2016 .

[28]  J. Godt,et al.  Deterministic estimation of hydrological thresholds for shallow landslide initiation and slope stability models: case study from the Somma-Vesuvius area of southern Italy , 2013, Landslides.

[29]  Tom Fawcett,et al.  An introduction to ROC analysis , 2006, Pattern Recognit. Lett..

[30]  Luca Brocca,et al.  Assessment of rainfall thresholds and soil moisture modeling for operational hydrogeological risk prevention in the Umbria region (central Italy) , 2012, Landslides.

[31]  M. Martina,et al.  Probabilistic rainfall thresholds for landslide occurrence using a Bayesian approach , 2012 .

[32]  Matthias Jakob,et al.  Hydrometeorological thresholds for landslide initiation and forest operation shutdowns on the north coast of British Columbia , 2006 .

[33]  Peter Molnar,et al.  Predictive performance of rainfall thresholds for shallow landslides in Switzerland from gridded daily data , 2017 .

[34]  J. Godt,et al.  Hillslope Hydrology and Stability , 2013 .

[35]  David R. Montgomery,et al.  Physics‐based continuous simulation of long‐term near‐surface hydrologic response for the Coos Bay experimental catchment , 2007 .

[36]  J A Swets,et al.  Measuring the accuracy of diagnostic systems. , 1988, Science.