164
10 A Sensitivity Analysis on the Gravity …
landslide and mudslide were 5.5 and 15.6, respectively. Meanwhile, the sensitivity
parameters of the slope gradient on the avalanche and WGE were both 4.6. All of
the parameters mentioned above were much larger than those of other triggers listed
in the Fig. 10.11. It is worth mentioning that slope height was the second most influential element on the maximum gravity erosion, of which sensitivity parameters on
the peak values of avalanche and WGE were 3.3 and 2.2, respectively. Nevertheless,
the majority of the sensitivity parameters shown in Fig. 10.11 are less than or close
to 1.0, which is much smaller than the maximum values above mentioned.
Accordingly, small changes in variables such as the duration and intensity of
rainfall events could cause major changes in gravity erosion, demonstrating the significant sensitivity of these dynamics to climate change on the Loess Plateau. The
result also suggests that rainfall duration-intensity and slope height-gradient are the
prominent influential inputs on the steep loess slope. It is worth noting that both of
these factors are potentially climate-driven: rainfall directly and landform through the
effects of temperature and moisture on the soil’s organic content (Sánchez-Canales
et al. 2015). Collectively, a positive increment of those variables is associated with
a positive increment of the failure amount and thus of the susceptibility level. If
we compare the degree of vertical variability of the variable relief with the variable
rainfall, we can observe that the strength of influence of the relief is lower than the
rainfall.
For the sensitivity analysis, an increase-rate-analysis method was tested, which
has never been previously employed in landslide susceptibility studies. As explained
earlier, the aim of sensitivity analysis was to detect trends, interactions between
variables, and non-linear behaviors. The approach allows a deeper understanding of
the failure mechanism, especially when we want to recognize the effect of each causal
factor and of the combination of factors on the susceptibility to gravity erosion. The
method is easy to understand, facile to calculate, and its result is easy to read. It holds
promise for research in other relevant fields of soil and water conservation.
10.4.6 Problems and Suggestions
This study will provide a tool for more reliable identification and analysis of site
conditions associated with different types of failure. It is important, however, to note
that although flume experiments are possibly the best approach to simulate natural slope failures, extrapolating these results to natural conditions requires caution
because natural soil variability and initial stress conditions are difficult to reproduce
in a flume study (Lourenço et al. 2006). Presently field tests on gravity erosion have
been conducted by the authors in the Liudaogou Catchment of the Loess Plateau, and
a comparison between the laboratory and field studies will be reported in the near
future. The method of sensitivity analysis presented here is a novel way to evaluate
the role of erosion triggers, especially in processing the results with limited data in
the experimental study. However, the reliability of the analysis conclusions depends
10 A Sensitivity Analysis on the Gravity …
landslide and mudslide were 5.5 and 15.6, respectively. Meanwhile, the sensitivity
parameters of the slope gradient on the avalanche and WGE were both 4.6. All of
the parameters mentioned above were much larger than those of other triggers listed
in the Fig. 10.11. It is worth mentioning that slope height was the second most influential element on the maximum gravity erosion, of which sensitivity parameters on
the peak values of avalanche and WGE were 3.3 and 2.2, respectively. Nevertheless,
the majority of the sensitivity parameters shown in Fig. 10.11 are less than or close
to 1.0, which is much smaller than the maximum values above mentioned.
Accordingly, small changes in variables such as the duration and intensity of
rainfall events could cause major changes in gravity erosion, demonstrating the significant sensitivity of these dynamics to climate change on the Loess Plateau. The
result also suggests that rainfall duration-intensity and slope height-gradient are the
prominent influential inputs on the steep loess slope. It is worth noting that both of
these factors are potentially climate-driven: rainfall directly and landform through the
effects of temperature and moisture on the soil’s organic content (Sánchez-Canales
et al. 2015). Collectively, a positive increment of those variables is associated with
a positive increment of the failure amount and thus of the susceptibility level. If
we compare the degree of vertical variability of the variable relief with the variable
rainfall, we can observe that the strength of influence of the relief is lower than the
rainfall.
For the sensitivity analysis, an increase-rate-analysis method was tested, which
has never been previously employed in landslide susceptibility studies. As explained
earlier, the aim of sensitivity analysis was to detect trends, interactions between
variables, and non-linear behaviors. The approach allows a deeper understanding of
the failure mechanism, especially when we want to recognize the effect of each causal
factor and of the combination of factors on the susceptibility to gravity erosion. The
method is easy to understand, facile to calculate, and its result is easy to read. It holds
promise for research in other relevant fields of soil and water conservation.
10.4.6 Problems and Suggestions
This study will provide a tool for more reliable identification and analysis of site
conditions associated with different types of failure. It is important, however, to note
that although flume experiments are possibly the best approach to simulate natural slope failures, extrapolating these results to natural conditions requires caution
because natural soil variability and initial stress conditions are difficult to reproduce
in a flume study (Lourenço et al. 2006). Presently field tests on gravity erosion have
been conducted by the authors in the Liudaogou Catchment of the Loess Plateau, and
a comparison between the laboratory and field studies will be reported in the near
future. The method of sensitivity analysis presented here is a novel way to evaluate
the role of erosion triggers, especially in processing the results with limited data in
the experimental study. However, the reliability of the analysis conclusions depends