World’s Soil Resources

10-year frequency
Ten-year frequency of landslides and associated mortality in Asia
Mortalities
120
7000
100
80
60
40
Frequency
Mortalities
6000
5000
4000
3000
2000
20
1000
0
1950 - 1959
1960 - 1969
1970 - 1979
1980 - 1989
1990 - 1999
2000 - 2009
0
Figure 7.10 Trends in landslide frequency and mortality on Asia. Source: FAO, 2011; EM-DAT, 2010.
7.7.1 | Soil landslide hazard
The depth of the soil mantle forming over mountainous topography reflects a natural balance between
soil production and soil erosion processes (Trustrum and De Rose, 1988; Heimsath et al., 1997). The primary
soil removal process in mountainous regions is landsliding, driven by the topographic relief and triggered by
climatic forcing such as rainfall or snowmelt (Iverson, 2000; Larsen, Montgomery and Korup, 2010; Kawagoe,
Kazama and Sarukkalige, 2009) or by earthquakes (Huang and Fan, 2013). Landslide damage is costly: Sidle
and Ochiai (2006) estimated the direct costs associated with rebuilding or replacing infrastructure at several
billion dollars per year, even without considering indirect costs related to construction and temporary loss of
site functionality. Similar estimates have been made just for Europe (Papathoma-Köhle et al., 2015).
Rainfall is the most common trigger for shallow landslides (Iverson, 2000). The strong relationship between
rainfall intensity-duration and landslide triggering conditions has prompted the use of rainfall characteristics
for early warning (Guzzetti et al., 2008; von Ruette, Lehmann and Or, 2014). The observed increase in
precipitation variability and in extreme events attributed to climate change has been linked to the observed
increase in landslide frequency in mountainous regions (Huggel, Clague and Korup, 2012). The recent IPCC
report (IPCC, 2012) lists evidence for the contiguous United States confirming statistically significant increases
in heavy (upper 5 percent) and very heavy (upper 1 percent) precipitation of 14 and 20 percent, respectively.
Moreover, evidence from Europe and the United States suggests that the relative increase in precipitation
extremes is larger than the increase in mean precipitation.
Schmidt and Dikau (2004) found that climatic scenarios representing unstable conditions of transition
from more humid to a dryer climate produced the highest slope instabilities. Soil hydraulic properties play an
important in imparting mechanical sensitivity. Indeed, the soil plays multiple roles in the landslide hazard, not
only as the mass that slides down the slope, but also through its own mechanical strength and through its
modulation of local hydrology via infiltration capacity, base flow, macropore flow and ground cover (Iverson,
2000; Sidle and Ochiai, 2006; Lehmann and Or, 2012). The partitioning of precipitation between infiltration,
overland flows and base flows is critical to the loading of the soil and to the ultimate soil failure. The mechanical
reinforcement by plant roots helps to stabilize the soil mantle (Abe and Ziemer, 1991; Schwarz, Cohen and Or,
2012), and bulk soil mechanical and hydraulic properties affect the susceptibility to failure.
Status of the World’s Soil Resources | Main Report The impact of soil change on ecosystem services
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