Search

In Alpine regions changes in seasonal climatic parameters, such as temperature, rainfall, and snow amount have already been observed. Specifically, in the South Tyrol area, meteorological observations indicate that temperatures are increasing and the number of snow days has generally diminished over time with perennial snow line now observed at higher elevations. Changes in rainfall have also been observed with more events associated with higher temperatures in the summer season. Natural hazards - mainly debris and mud flows, landslides, avalanches, rock falls, and (flash) floods - that affect this area every year, damaging population and infrastructures, are either weather or cryosphere-related. While these events have been recorded sporadically since the beginning of the 20th century, a systematic approach of their inventory has been done by local authorities since the 1990s. So far, Earth observation data has not been exploited to complete or complement existing inventories nor have they been used to investigate the influence of climate perturbation on potentially dangerous natural phenomena. The research presented here thus has three objectives: (i) analyse long time series of climate data and hazard occurrence in South Tyrol to examine if these records exhibit a coherent response of hazards to changes in climate; (ii) measure the spatio-temporal evolution of climatic and natural hazard events recorded, and (iii) explore potential relations between meteorological conditions and the hazard occurrence. In this context, in-situ and satellite-based climate data are exploited to study natural hazard triggers while the potential of Earth observation data is evaluated as a complement to the existing historical records of natural hazards. Specifically, Copernicus Sentinel-1 images are used to detect the spatio-temporal distribution of slow earth surface deformations and the results used for checking the completeness of the actual slow-moving landslide inventories. Hazard-related changes in the South Tyrolian landscape have also been analysed in relation to particular meteorological events at a regional scale, assessing trends and anomalies. Results show that: (i) satellite data are very useful to complement the existing natural hazard inventories; (ii) in-situ and satellite-based climate records show similar patterns but differ due to regional versus local variability; (iii) even in a data-rich region such as the analysed area, the overall response of natural hazard occurrence, magnitude, and frequency to change in climate variables is difficult to decipher due to the presence of multiple triggers and locally driven ground responses. However, an increase in the average annual duration of rainfall events and debris flow occurrence can be observed.

In this report, we summarise the activities of the Research Institute for Geo-Hydrological Protection (IRPI, http://www.irpi.cnr.it/en/ ), of the Italian National Research Council (CNR, http://www.cnr.it/en/ ), as a World Centre of Excellence (WCoE) on Landslide Risk, of the International Programme on Landslides (IPL, http://iplhq.org ). The report is organised as follows. After a brief description of CNR IRPI (“The Research Institute for Geo-Hydrological Protection”), we present recent developments related to landslide early warning systems (“Landslide early warning systems”), climate change and landslides interactions (“Landslides in a changing climate”), and landslide risk assessment, mitigation and dissemination efforts (“Landslide risk assessment, mitigation and dissemination efforts”). We conclude listing relevant papers published between 2017 and 2018 by CNR IRPI scientists (“References”).

Earth observation (EO) data are useful tools to analyse geomorphological processes, among which slow-moving landslides triggered by rainfall. EO data are also used to evaluate climate change and to assess its impact on geomorphological processes and geo-hydrological phenomena. The latter is the topic of the Project OT4Clima (Innovative Earth Observation technologies to study Climate Change and its impact on the environment) joined by CNR-IRPI within a consortium that includes other CNR institutes, universities and private companies. The OT4CLIMA project moves from the awareness that the impacts of climate change on the environment need to be better observed, understood, and modelled, especially at a regional scale, in order to put in place appropriate and effective risk mitigation strategies. Within the project, the CNR-IRPI group works on the development of rigorous methods and procedures for evaluating the impact of climate and its change on landslides, in particular on those characterized by a slow cinematic, at a regional scale. The test site is represented by four catchments located in the Basilicata region, southern Italy, namely the basins of the Bradano, Basento, Agri, and Sinni rivers. Long-term rainfall series gathered from 22 rain gauges located in the four catchments are analysed to evaluate the presence of temporal trends. To this aim, non-parametric and statistical tests are applied to the series. Historical landslide information is gathered from the analysis of the IFFI (Inventario dei Fenomeni Franosi in Italia) database, the Idrogeo platform (https://idrogeo.isprambiente.it/app/) and the AVI (Aree Vulnerate in Italia) catalogue. Only some types of landslide movements are considered, namely rotational-translational slides, slow slides/flows, complex movements. Moreover, Copernicus Sentinel-1 images are employed to detect the spatial and temporal distribution of slow earth surface deformations. The obtained results are used for checking the completeness of the landslide inventories. More in detail, the deformation maps of the test site are obtained by means of the application of the SBAS (Small BAseline Subset) technique to three datasets of Sentinel-1 images: t146 ascending orbit and t51 and t124 descending orbits, for the period 2015-2020. Then, a comparative analysis of rainfall data with displacement series is carried out with the aim of identifying clusters of satellite measurements with homogeneous behaviour likely correlated to variations in the rainfall regime. In particular, only the points with a mean velocity in the observation higher than 0.1 cm/year are considered to be moving. Moreover, only the displacement series of points located in areas mapped as landslides - as for the historical inventories - and sited within the influence regions of each rain gauge in the study area are analysed. A 10-km circular buffer centred in the stations are used to define the influence region of each station. The displacement series are analysed and compared to the rainfall series to search for correlations and to evaluate the effects of climate drivers on slow moving landslides.

Although mass-movements can be caused by a variety of natural phenomena and human actions, in most areas of the world rainfall is their primary trigger. An often-neglected complication of the operational forecasting of rainfall-induced landslides is global warming, in particular the related ongoing and expected changes in rainfall and temperature. The evaluation of the effects of the current and the projected climate change on the stability/instability conditions of natural and engineered slopes remains complicated. In this chapter, we address the main questions related to the assessment of the impact of climate change on mass-movements. Starting from the results of a review of studies on the topic, we analyze and discuss how climate factors (and their changes) influence slope stability conditions and landslide hazard. This is not trivial, due to multiple reasons, including the fact that (i) the temporal and the geographical scales of climate and landslides are very different; (ii) different climate variables affect landslides; (iii) landslides are complex and diversified phenomena that respond differently to changes in climate. Moreover, we outline the main research needs and we provide general and specific recommendations for the operational forecasting of rainfall-induced landslides considering the current and the expected changes in climate. In particular, a holistic approach is needed to understand and measure how climate variables and their variability affect mass-movements, and to provide useful projections that will allow effective short- and long-term actions to reduce landslide risk.

Analyses of historical records of landslides and climate variables are useful tools to search for correlations between damaging landslide events and their triggers. In this work, we investigate the temporal and geographical relationships between two long-term historical series of catalogued landslide occurrences and daily rainfall data in Umbria, a central Italian region, from 1928 to 2001. Moreover, we search for changes in the frequency and density of landslides, and in the characteristics of the associated rainfall events. Using a consolidated approach, partially modified, we find that the rainfall events that have produced rainfall-induced landslides in Umbria changed in space and time during observation period and between two considered sub-periods (1928-1975 and 1976-2001). In particular, we find that: (i) the monthly distribution of landslides associated with rainfall events is quite different than that of all landslides in the regional catalogue; (ii) the spatial and temporal distribution of REL changed from the older (most events occurred in winter) to the recent period (most events occurred in autumn); (iii) the recent most rainfall events associated with landslides are characterized by a lower cumulated rainfall and a shorter duration, sign of an increased propensity of the regional territory to produce landslides over time.

Hydrogeological hazards now exacerbated by the ongoing climate change pose serious challenges for the safety of the population worldwide. Among the others, the landslide risk can be mitigated by setting up efficient and reliable early warning systems. To date, rainfall thresholds are one of the most used tools to forecast the possible occurrence of rainfall-induced failures in large regions. In Italy a dense rain gauge network with hourly or sub-hourly temporal resolution is available. However, in some developing countries, where ground measurements are still absent or are available at coarser (daily) temporal resolution, satellite-based rainfall estimates could be a vital alternative. For this purpose, the reliability of rainfall thresholds defined using both satellite (SB) and ground-based (GB) data and with hourly or daily temporal resolution is assessed in a study area comprising the Abruzzo, Marche and Umbria regions (AMU), central Italy. The comparison between the performance of the different products allows to test their capability in eventually can GB rainfall measurements are gathered at hourly time steps (OBS-H) from a national network and aggregated on a daily scale (OBS-D); SB rainfall estimates are retrieved from the Climate Prediction Center Morphing Technique (CMORPH, hourly resolution), and from the SM2RASC product, based on the application of SM2RAIN algorithm to ASCAT (Advanced SCATterometer) soil moisture product (daily resolution). Results show that thresholds defined with GB rainfall data perform better than those obtained using SB estimates regardless of the temporal resolution. CMORPH and SM2RASC thresholds are still able to predict landslide occurrence although with a high number of false predictions.

Land use and land cover (LULC), as well as their geographical and temporal variations, affect landslide occurrence and the related risk, in ways that are difficult to determine. Here, we propose a method for the regional analysis of variations in landslide frequency and distribution in response to observed and projected LULC changes. The method is quantitative and reproducible. We test it in Calabria, southern Italy, where a catalogue of 7037 landslides occurred between 1921 and 2010 is available. First, we defined empirical relationships linking the observed LULC variations to landslide occurrence. We found that, in the period 1921-1965, the majority of the landslides occurred in forests and grassland areas, while, in the period 1966-2010, the landslide density became higher in grassland areas, lower in arable lands and remained about constant in the forests. We consider this an evidence of the positive effect of agricultural practices and land management in reducing landslide occurrence. We noticed that both the landslide occurrence and the distribution of the vulnerable elements changed in the observation period. Then, we calculated the projected variations (to 2050) in landslide occurrence related to 32 scenarios of LULC changes. Our projections reveal a modest increase in landslide occurrence in all scenarios, in the range from 0.9 to 3.2%, with an average increase of 2%. Considering all scenarios, we expect an increase in the number of landslides due to LULC variations in 291 municipalities in Calabria (71%), with 4 municipalities where the increase is expected to exceed 50%. We maintain that the observed and the projected variations in the occurrence of landslides in Calabria are related to changes in natural (i.e. the number and distribution of the triggering events) and environmental and societal (i.e. the number and the distribution of the exposed elements) components.

Scientific community recognizes warming of the Earth climate system unequivocal. The warming could induce substantial climate changes (CC) with relevant variations due to the region, weather patterns and time horizon of interest. In this perspective, the impact of CC on weather-induced disasters represents a crucial topic also due to the associated high socio-economic costs. However, the quantitative evaluation of the impact of CC on landslide occurrence, activity, and frequency remains a complex scientific question. Moreover, also land use and land cover (LULC), and their variations, affect landslide occurrence and the related risk. According to the fifth report of the Intergovernmental Panel on Climate Change, an increase in the frequency and the intensity of extreme rainfall is expected in the Mediterranean area. This might result in a variation in the temporal and spatial distribution of rainfall-induced landslides, and in an increase in the size of the population exposed to landslide risk. Exploiting detailed landslide information, climatic, and LULC data, and future projections in a Mediterranean region (Calabria, Southern Italy), we propose three linked methods - quantitative and reproducible - for the regionalscale evaluation of past and future variations in the occurrence of rainfall-induced landslides, in response to changes in climate (rainfall regimes) and LULC. First, using historical landslide information and daily rainfall in Calabria between 1921 and 2010, we study the temporal and the geographical variation in the occurrence of 1466 Rainfall Events with Landslides (REL; the occurrence of at least 1 landslide during or immediately after a rainfall event) and in their impact on the population. We find changes in the geographical and temporal distributions of REL, and in their rainfall characteristics. In addition, we evaluate the impact of the events on the population, revealing a complex picture of changes. Second, we use a subset of the previous dataset, related to the reference period 1981-2010, and high-resolution climate projections based on RCP4.5 and RCP8.5 scenarios for the future period 2036-2065. Calculating correlations between REL occurrence and weather variables estimated in the reference period, we assess future variations in REL occurrence, expecting a substantial regional increase in REL occurrence for the period 2036-2065, under both scenarios. We also investigate future variations in the impact of REL on the population, finding higher increases. Third, using the whole landslide dataset and two maps of LULC of the region (released in 1956 and 2000) we define empirical relationships linking the observed LULC variations to landslide occurrence, finding changes in the spatial distribution of landslides. Then, we calculate the projected variations (to year 2050) in landslide occurrence related to 32 scenarios of LULC changes, revealing a modest increase in landslide occurrence in all of them. We uphold that the observed and the projected variations in the occurrence of rainfall-induced landslides in the study area are related to interlaced changes in triggering, environmental, and societal components.

Only a few studies have investigated the geographical and temporal variations in the frequency and distribution of rainfall-induced landslides, and the consequences of the variations on landslide risk. Lack of information limits the possibility to evaluate the impact of environmental and climate changes on landslide frequency and risk. Here, we exploit detailed historical information on landslides and rainfall in Calabria, southern Italy, between 1921 and 2010 to study the temporal and the geographical variation in the occurrence of rainfall-induced landslides and in their impact on the population. We exploit a catalogue with information on historical landslides from June 1920 to December 2010, and daily rainfall records obtained by a network of 318 rain gauges in the same period, to reconstruct 448 493 rainfall events (RE). Combining the rainfall and the landslide information, we obtain a catalogue of 1466 rainfall events with landslides (REL), where an REL is the occurrence of one or more landslide during or immediately after a rainfall event. We find that (i) the geographical and the temporal distributions of the rainfall-induced landslides have changed in the observation period, (ii) the monthly distribution of the REL has changed in the observation period, and (iii) the average and maximum cumulated event rainfall that have resulted in landslides in the recent 30-year period 1981–2010 are lower than the rainfall necessary to trigger landslides in previous periods, whereas the duration of the RE that triggered landslides has remained the same. We attribute the changes to variations in the rainfall conditions and to an increased vulnerability of the territory. To investigate the variations in the impact of REL on the population, we compared the number of REL in each of the 409 municipalities in Calabria with the size of the population in the municipalities measured by national Censuses conducted in 1951, 1981, and 2011. We adopted two strategies; the first strategy considered impact as IREL = #REL / P, and the second strategy measured impact as RREL = #REL × P, where #REL is the total number of REL in a period, and P is the size of the population in the same period and geographical area. The analysis has revealed a complex pattern of changes in the impact of rainfall-induced landslides in Calabria in the recent past, with areas where IREL and RREL have increased, and other areas where they have decreased. Municipalities where IREL has increased are mainly in the mountains, and municipalities where RREL has increased are mainly along the coasts. The complexity of the changes in the frequency and impact of rainfall-induced landslides observed in Calabria suggests that it remains difficult and uncertain to predict the possible variations in the frequency and impact of landslide in response to future climatic and environmental changes.

Changes in the main weather features are becoming perceivable in Italy. In the last years, the average temperature and the intensity of rainstorms are increasing. Such phenomena could lead to changes in the earth-atmosphere interaction. Accounting for the high vulnerability of the Italian territory, an obvious consequence would concern the effects on the hydro-geological hazards, including landslides and floods. As a matter of fact, the higher frequency of high magnitude flood and landslide events represent an alarm bell. It is necessary to explore with all available instruments the consequences of the potential climate changes. Since quantitative predictions are not possible, the only way to run is depicting rational scenarios for the most vulnerable contexts adopting a multidisciplinary approach. Based on projections of potential climate changes in the 21st century, the report examines their potential impact in the context of the Italian peninsula. After a general overview about typical slope responses to weather forcing some quantitative scenarios have been depicted for representative geomorphological contexts. The last part of the paper examines changes in the expected risk, based on the characteristics of the Italian territory and its vulnerability, looking at the initiatives to undertake for its mitigation.

Urbanization in hazardous regions, the abandonment of rural and mountain areas, and changed agricultural and forest practices have increased the impact of landslides through the years. Hence, the changing climate variables, like rainfall, acted and will act on a human-modified landscape. In this work, we analyze the role of rainfall variation and land use/cover change in the occurrence of landslides in Calabria in the period 1921–2010. Combining rainfall and landslide information, we reconstruct and analyze a catalogue of 1466 rainfall events with landslides (i.e., the occurrence of one or more landslide during or immediately after a rainfall event). To investigate the impact of land use/cover changes in the occurrence of landslides, we consider the “Land Use Map” made by the Italian National Research Council and the Italian Touring Club in 1956, and the “CORINE Land Cover” map released in 2000. Since our landslide catalogue is at municipality scale (i.e., for each landslide we known the municipality in which it occurred), we attribute a prevailing land use/cover class to each of the 409 municipalities of Calabria. We split the catalogue in two subsets (1921–1965 and 1966–2010) and correlate the landslides occurred in the first period to the 1956 land use and the landslides occurred in the second period to the 2000 land cover. We find that: (i) the geographical and the temporal distributions of rainfall-induced landslides have changed in the observation period; (ii) land use/cover in Calabria has changed between the two periods, with a huge decrease of arable land and an increase of heterogeneous agricultural areas and forests; (iii) in both periods, most of the landslides occurred in areas characterized by forests and arable land; (iv) in the second period, there was an increase (decrease) of landslides occurred in agricultural areas (arable land).

According to the fifth report of the Intergovernmental Panel on Climate Change, "warming of the climate system is unequivocal". The influence of climate changes on slope stability and landslides is also undisputable. Nevertheless, the quantitative evaluation of the impact of global warming, and the related changes in climate, on landslides remains a complex question to be solved. The evidence that climate and landslides act at only partially overlapping spatial and temporal scales complicates the evaluation. Different research fields, including e.g., climatology, physics, hydrology, geology, hydrogeology, geotechnics, soil science, environmental science, and social science, must be considered. Climatic, environmental, demographic, and economic changes are strictly correlated, with complex feedbacks, to landslide occurrence and variation. Thus, a holistic, multidisciplinary approach is necessary. We reviewed the literature on landslide-climate studies, and found a bias in their geographical distribution, with several studies centered in Europe and North America, and large parts of the world not investigated. We examined advantages and drawbacks of the approaches adopted to evaluate the effects of climate variations on landslides, including prospective modelling and retrospective methods that use landslide and climate records, and paleoenvironmental information. We found that the results of landslide-climate studies depend more on the emission scenarios, the global circulation models, the regional climate models, and the methods to downscale the climate variables, than on the description of the variables controlling slope processes. Using ensembles of projections based on a range of emissions scenarios would reduce (or at least quantify) the uncertainties in the obtained results. We performed a preliminary global assessment of the future landslide impact, presenting a global distribution of the projected impact of climate change on landslide activity and abundance. Where global warming is expected to increase, the frequency and intensity of severe rainfall events, a primary trigger of shallow, rapid-moving landslides that cause many landslide fatalities, an increase in the number of people exposed to landslide risk is to be expected. Furthermore, we defined a group of objective and reproducible methods for the quantitative evaluation of the past and future (expected) variations in landslide occurrence and distribution, and in the impact and risk to the population, as a result of changes in climatic and environmental factors (particularly, land use changes), at regional scale. The methods were tested in a southern Italian region, but they can easily applied in other physiographic and climatic regions, where adequate information is available.

The anthropogenic global warming could significantly affect weather patterns, with variable impacts at the regional scale. Geo-hydrological hazards represent an interesting example of the possible impacts. We present a study of the effects of potential climate change on slope stability conditions in two different contexts in the Italian Apennines. Although the two examined sites are 400 km apart, climate simulations return similar variations in weather patterns, which are characterized by a strong increase in air temperature, a reduction in seasonal cumulative precipitation, and an increase in daily precipitation. In spite of the similar input, the response of the two sites, lying respectively on saturated clays and on unsaturated non-plastic silts, might be completely different. Although these studies do not currently provide quantitative estimates, they represent a valuable support to policy makers and communities for the definition and prioritization of adaptation actions and for investments to cope with the expected climate changes.

The rainfall erosivity, playing a decisive role into erosion and degradation of soils, is a relevant factor for land-use planning and environmental risk assessment. Its decisive role must be studied by also taking in mind the outlook of climate change. The observations needed to determine the erosivity with adequate temporal and spatial detail, however, are rarely available. The aim of this study consists in assessing the spatial and seasonal distribution of rainfall erosivity in the Mediterranean environment. A regional analysis of erosivity was conducted considering more than 45 thousands erosive rainstorms in Calabria (Southern Italy). A network of 155 rain gauges, well distributed over the region, provided the necessary information with a time detail of 5 min between 1989 and 2008. After a concise review of the literature, three time scales were considered: monthly, daily and "single event" scale. A power law relationship between the values of rainfall and erosivity, obtained by analysing the erosive rainstorms, was applied, showing systematic seasonal variations. The climatic control on erosivity was well described by regression equations formed by a constant value (wet period) and a cosine curve (dry months). This seasonal trend testifies that a greater erosivity per unit of rainfall has to be expected in the driest months. In addition, altitude ranges in Calabria from sea level to over 2,000 m a.s.l., affecting the rainfall regime. Considering this aspect, the regression equations were slightly improved by including the influence of the altitude in the analysis of erosivity. The erosivity maps, achievable in the Mediterranean climate area through the methods and equations proposed in this paper, can provide a significant contribution towards the modelling of detachment and transport of soil particles at the catchment scale. © 2014 Springer-Verlag Berlin Heidelberg.

According to the fifth report of the Intergovernmental Panel on Climate Change, an increase in the frequency and the intensity of extreme rainfall is expected in the Mediterranean area. Among different impacts, this increase might result in a variation in the frequency and the spatial distribution of rainfall-induced landslides, and in an increase in the size of the population exposed to landslide risk. We propose a method for the regional-scale evaluation of future variations in the occurrence of rainfall-induced landslides, in response to changes in rainfall regimes. We exploit information on the occurrence of 603 rainfall-induced landslides in Calabria, southern Italy, in the period 1981–2010, and daily rainfall data recorded in the same period in the region. Furthermore, we use high-resolution climate projections based on RCP4.5 and RCP8.5 scenarios. In particular, we consider the mean variations between a 30-year future period (2036–2065) and the reference period 1981–2010 in three variables assumed as proxy for landslide activity: annual rainfall, seasonal cumulated rainfall, and annual maxima of daily rainfall. Based on reliable correlations between landslide occurrence and weather variables estimated in the reference period, we assess future variations in rainfall-induced landslide occurrence for all the municipalities of Calabria. A + 45.7% and + 21.2% average regional variation in rainfall-induced landslide occurrence is expected in the region for the period 2036–2065, under the RCP4.5 and RCP8.5 scenario, respectively. We also investigate the future variations in the impact of rainfall-induced landslides on the population of Calabria. We find a + 80.2% and + 54.5% increase in the impact on the population for the period 2036–2065, under the RCP4.5 and RCP8.5 scenario, respectively. The proposed method is quantitative and reproducible, thus it can be applied in similar regions, where adequate landslide and rainfall information is available.