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A Landslide Initiation Threshold Using Data from Hydrologic Monitoring Sites in Cayey, Maricao, and Ciales, Puerto Rico

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Soil Erosion Research Under a Changing Climate, January 8-13, 2023, Aguadilla, Puerto Rico, USA  .(doi:10.13031/soil.23526)
Authors:   Jonathan E. Pérez Paulino, K. Stephen Hughes
Keywords:   HydroMet, Landslide initiation, Mass-wasting, Shallow mass-wasting.

Abstract

Water and mass-wasting are related, in that the more water present, the more likely it is for a landslide to happen (Thomas et al., 2020). This is significant for Puerto Rico since the peak of hurricane seasons present the most severe rainfalls (Larsen and Simon, 1993), which could increase owing to climate change. The mass-wasting events that usually occur in these events are shallow; according to Hughes and Schulz (2020), shallow mass-wasting events transport sediment to the fluvial network through debris flows. For the development of landslide initiation thresholds, there is a bilinear hydrometeorological approach that takes soil saturation and precipitation into account. As a method for applying this concept, HydroMet was created. It is a Python program that plots a graph based on two parameters, such as rainfall and soil saturation, in order to forecast the onset of possible landslides (Conrad et al., 2021). When considering soil saturation and rainfall, four alternative statistical methods can be used to determine the ideal threshold, which determines whether a landslide is likely to occur or not based on the factors computed; these are Threat Score, Precision, True Skill Statistic, and Optimal Point (Conrad et al., 2021). In light of this, landslide forecasting potential was investigated utilizing hydrologic monitoring sites in Cayey, Maricao, and Ciales using a hydro-meteorological approach. These supplied precipitation and hydrologic data, for which they were used in HydroMet to determine statistical thresholds using the four different statistical approaches to analyze the precipitation and antecedent soil moisture needed to produce groundwater conditions that are a proxy for landslide initiation (Conrad et al., 2021). Using Threat Score, it was discovered that 33 mm of rain over the course of 24 hours and an antecedent soil moisture value of 0.85 were required to start a potential landslide. Using Precision, it was discovered that 52 mm of rain over the course of 24 hours and an antecedent soil moisture value of 0.50 were required to initiate a potential landslide. According to the True Skill Statistic and Optimal Point methods, groundwater reaction that could cause landslides requires 33 mm of rainfall accumulation over the course of 24 hours and a value of 0.80 for antecedent soil moisture. Considering the sociological conditions for each of these three sectors and the percentage of anthropological structures that may be impacted by these occurrences, a decision may be made on which of the four statistical approaches might be used for making decisions.

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