Characteristics of Rainfall Events Triggering Landslides in Two Climatologically Di erent Areas: Southern Ecuador and Southern Spain
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Materia
Critical Rainfall Thresholds Climate cycles Trigger factors Correlation
Date
2020-07-21Referencia bibliográfica
Palenzuela Baena, J. A., Soto Luzuriaga, J., & Irigaray Fernández, C. (2020). Characteristics of rainfall events triggering landslides in two climatologically different areas: Southern Ecuador and Southern Spain. Hydrology, 7(3), 45. [
Sponsorship
Spanish Government CGL2008-04854; Ministry of Higher Education, Science, Technology and Innovation (SENESCYT) under the scholarship program "Open Call 2012 Second Phase" of the government of EcuadorAbstract
In the research field on landslide hazard assessment for natural risk prediction and
mitigation, it is necessary to know the characteristics of the triggering factors, such as rainfall and
earthquakes, as well as possible. This work aims to generate and compare the basic information on
rainfall events triggering landslides in two areas with di erent climate and geological settings: the
Loja Basin in southern Ecuador and the southern part of the province of Granada in Spain. In addition,
this paper gives preliminary insights on the correlation between these rainfall events and major
climate cycles a ecting each of these study areas. To achieve these objectives, the information on
previous studies on these areas was compiled and supplemented to obtain and compare Critical
Rainfall Threshold (CRT). Additionally, a seven-month series of accumulated rainfall and mean
climate indices were calculated from daily rainfall and monthly climate, respectively. This enabled
the correlation between both rainfall and climate cycles. For both study areas, the CRT functions
were fitted including the confidence and prediction bounds, and their statistical significance was also
assessed. However, to overcome the major di culties to characterize each landslide event, the rainfall
events associated with every landslide are deduced from the spikes showing uncommon return
periods cumulative rainfall. Thus, the method used, which has been developed by the authors in
previous research, avoids the need to preselect specific rainfall durations for each type of landslide.
The information extracted from the findings of this work show that for the wetter area of Ecuador,
CRT presents a lower scale factor indicating that lower values of accumulated rainfall are needed to
trigger a landslide in this area. This is most likely attributed to the high soil saturation. The separate
analysis of the landslide types in the case of southern Granada show very low statistical significance
for translational slides, as a low number of data could be identified. However, better fit was obtained
for rock falls, complex slides, and the global fit considering all landslide types with R2 values
close to one. In the case of the Loja Basin, the ENSO (El Niño Southern Oscillation) cycle shows a
moderate positive correlation with accumulated rainfall in the wettest period, while for the case of
the south of the province of Granada, a positive correlation was found between the NAO (North
Atlantic Oscillation) and the WeMO (Western Mediterranean Oscillation) climate time series and the
accumulated rainfall. This correlation is highlighted when the aggregation (NAO + WeMO) of both
climate indices is considered, reaching a Pearson coe cient of –0.55, and exceeding the average of the
negative values of this combined index with significant rates in the hydrological years showing a
higher number of documented landslides.