Determination of rainfall thresholds for shallow landslides by a probabilistic and empirical method

Abstract

Abstract. Rainfall-induced landslides not only cause property loss, but also kill and injure large numbers of people every year in mountainous areas in China. These losses and casualties may be avoided to some extent with rainfall threshold values used in an early warning system at a regional scale for the occurrence of landslides. However, the limited availability of data always causes difficulties. In this paper we present a method to calculate rainfall threshold values with limited data sets for the two rainfall parameters: maximum hourly rainfall intensity and accumulated precipitation. The method has been applied to the Huangshan region, in Anhui Province, China. Four early warning levels (Zero, Outlook, Attention, and Warning) have been adopted and the corresponding rainfall threshold values have been defined by probability lines. A validation procedure showed that this method can significantly enhance the effectiveness of a warning system, and finally reduce the risk from shallow landslides in mountainous regions.

Precipitation Thresholds for Triggering Floods in the Corgo Basin, Portugal

“…Lower and upper limits of precipitation thresholds were defined for the Corgo basin taking into account the selected set of flood events triggered by precipitation from 1946 to 1998 ( Figure 5). Figure 5 also includes, for validation, the potential regression line that best fits the distribution of flood events and the highest annual previous precipitation value for each combination of cumulative days (1,2,3,4,5,10,15,20,30,40,50,60,75, and 90) recorded in the years with no floods for the same period. The lower limit threshold is better fitted by a linear regression described by y = 10.82x + 76.84 which typifies the minimum precipitation conditions for flood triggering in the study area.…”

“…Some studies [4,43] that criticize these approaches, have introduced some statistical methods for the definition of more objective precipitation intensity-duration thresholds [42]. However, these methods involve hourly precipitation data (e.g., [5,14,20,30,42]) which in Portugal are too scarce or even absent in most drainage basins. Therefore, the empirical thresholds estimated in this study, are based on the identification of past flood events and include (i) the computation of antecedent precipitation threshold defined by linear regression; (ii) the normalization of precipitation by the mean annual precipitation; (iii) the definition of lower limit and upper limit precipitation thresholds; and (iv) the definition of combined precipitation thresholds, which integrates the precipitation event and the antecedent precipitation for different time periods.…”

“…Another limitation is that the precipitation thresholds obtained are valid only for the Corgo basin. This constraint , as suggested by Huang, Ju, Liao and Liu [20], must be taken into account before applying the methodology to another area. The variability in precipitation thresholds can be due to several factors, such as: (i) lithological or morphological diversity, vegetation and soil conditions; (ii) different climatic regimes and weather circumstances; (iii) the heterogeneity and the incomplete precipitation data and floods used to determine thresholds.…”

“…Next, and in order to validate the thresholds, the critical combinations of accumulated absolute precipitation, the duration of the events that triggered floods, as well as the records of maximum accumulated precipitation for different time intervals (1,2,3,4,5,10,15,20,30,40,50, 60, 75, 90 days) that occurred in years with no flood events were all considered for the precipitation station with the highest coefficient of determination (Lamas de Olo) between critical combination (quantity/duration). A normalization procedure was applied as recommended in previous studies (e.g., [8,12,41]) in order to reduce discrepancies in precipitation values due to the different elevations of the meteorological stations.…”

“…Several works have focused on the estimation of precipitation thresholds and their use in the prediction of landslides triggered by precipitation [4,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In spite of being considered one of the emerging approaches in flood forecasting [6], applied research to flood-related precipitation thresholds have been more limited than the applied research to landslides [24].…”