Assessment of the Relationship Between Daily and Total Multi-Day Precipitation Sums and Landslide Activation in the Regions of Georgia

Abstract

A detailed statistical analysis of the relationship between daily and accumulated multi-daily precipitation sums and the number of landslides in 12 regions of Georgia is presented. Landslide data with a known days of activation were used (a total of 519 landslide events from 1968 to 2022). For the analysis, the precipitation sum for the day of landslide activation (P1) was determined, as well as the accumulated precipitation sum for 3 days (P3), 5 (P5), 7 (P7), 10 (P10), 20 (P20) and 30 days (P30)   prior to landslide occurrence (including the day with landslide).

Specifically, the following results were obtained. The relationship between average precipitation values (threshold values) and daily precipitation duration during the day of landslide activation and before 3, 5...30 days of landslides activation in Georgia and its individual regions was determined. It was found that, overall, in eastern Georgia (including the Samtskhe-Javakheti region), landslide activation occurs with significantly lower precipitation sums than in western Georgia. The average P1 values are 8.8 and 11.9 mm, respectively, and the P30 values are 75.2 and 156.6 mm. The linear correlation between the number of landslides and the P1…P30 values across the regions of Georgia is high for P1,P3,P20 and P30 and moderate for P5,P7 and P10. For Georgia the sum of precipitation associated with landslides exceeds the general long-term mean daily precipitation sum by approximately 95%. For Georgia as a whole and its Eastern and Western parts, the dependence of the number of landslides on the P1 ... P30 values have the form of a third-degree polynomial (sequentially: slight increase – plateau – strong increase). For P1 values, the precipitation sum plateau, after which a strong increase in the number of landslides begins, covers the range from 6.3 to 30.8 mm, and for P30 – from 62.4 to 189.5 mm (the total relative number of landslides is ≈ 42.1–43.3%).