Statistical inference of the relations among air temperature, land-use change, and rockfall hazard

Climate change has widespread impacts on human and natural systems worldwide. The pronounced air temperature warming detected worldwide could explain unusual events, as for example the increment of extreme precipitation events, increased incidence of summer heatwaves and slope instability. The possible presence of non-climatic forcings affecting temperature records, as for example land-use and land-cover changes, could introduce significant bias in the records and uncertainty on global overall temperature trends. This could somehow alterate, on the one hand, the perception of global warming, and on the other hand, all temperature-related analyses and models. Nevertheless, a robust assessment of climate warming patterns entails not only the analysis of all climate variables involved, but also the full understanding of the impacts on the natural systems, as for example the cryosphere, that could be used as terrestrial indicators of climate change. Chapter 1 shed light on the main scientific question investigated in the thesis, presenting the proposed investigation strategy, and the techniques applied. After an introduction on the issue of increasing air temperature vaiability in the current context of climate change, the two macrotopics of the thesis are presented and briefly outlined (Chapter 2 and 3). In Chapter 2, we investigate the nexus between temperature variations and urbanization trends, by analysing data recorded from weather instruments worldwide. After an extended introduction on the Urban Heat Island effect and its implications for climate warming trends at regional and global scale, we propose several methods to investigate the presence of a possible relation between air temperature variations and urbanizations dynamics with time, based on nightlights satellite measurements as proxy of urbanization. We applied a global scale analysis on more than 5000 temperature stations from the Berkeley Earth dataset in the period 1992-2013. Results highlight the tendency of urbanization to affect temperature trend at continental and regional scales. Significant positive concordant trends in temperature and nightlights variations have been detected, especially in developing and emerging regions, where the effects of growing urbanization are more evident. In Chapter 3 we turn to investigate the effects of air temperature variations on the hydrogeological hazard risk in those environments that are among the most sensitive to climate change, i.e. the high elevation sites. In alpine areas, and in particular in high mountain areas, the potential effects of environmental changes on air temperature data are minimum, since these areas are only slightly affected by urbanization dynamics and land-use changes. More in detail, in Chapter 3, we propose a statistical-based tool for the detection of the role of temperature, in association with other climate-related variables (as precipitation), in the triggering of slope stability. This approach is aimed to point out the potential climatic triggering climate factors for the slope failure. It has thought up as a tool for a better comprehension of the possible effects of air temperature variations on environmental dynamics, also in the presence of sparse and poor-quality data. We performed this method on a catalogue of 41 rockfalls in the Italian Alps, focusing on the role of temperature on slope instability preparation and initiation, and on cryosphere-related dynamics. The final purpose is detecting a possible linkage between slope failures and meteorological anomalies, and results suggest a major role of temperature as a preparatory/triggering factor. Rockfalls occurred in association with significant temperature anomalies in 83% of our case studies, and different regional patterns emerge from the data. Based on these results, temperature can be considered as a key factor contributing to slope failure occurrence in different ways, in presence of both warm and cool temperature anomalies. Chapter 4 presents a critical analysis in terms of how much it could be really answered of the main scientific questions with this work, what are the limitations encountered, which questions remain open and the possible further developments

Climate anomalies associated with the occurrence of rockfalls at high-elevation in the Italian Alps

Climate change is seriously affecting the cryosphere in terms, for example, of permafrost thaw, alteration of rain ∕ snow ratio, and glacier shrinkage. There is concern about the increasing number of rockfalls at high elevation in the last decades. Nevertheless, the exact role of climate parameters in slope instability at high elevation has not been fully explored yet. In this paper, we investigate 41 rockfalls listed in different sources (newspapers, technical reports, and CNR IRPI archive) in the elevation range 1500–4200 m a.s.l. in the Italian Alps between 1997 and 2013 in the absence of an evident trigger. We apply and improve an existing data-based statistical approach to detect the anomalies of climate parameters (temperature and precipitation) associated with rockfall occurrences. The identified climate anomalies have been related to the spatiotemporal distribution of the events. Rockfalls occurred in association with significant temperature anomalies in 83 % of our case studies. Temperature represents a key factor contributing to slope failure occurrence in different ways. As expected, warm temperatures accelerate snowmelt and permafrost thaw; however, surprisingly, negative anomalies are also often associated with slope failures. Interestingly, different regional patterns emerge from the data: higher-than-average temperatures are often associated with rockfalls in the Western Alps, while in the Eastern Alps slope failures are mainly associated with colder-than-average temperatures

Climatic conditions associated to the occurrence of slope instabilities in the Italian Alps in year 2016

Studies carried out in different parts of the world have shown that, in the mountain high-elevation sites, temperature can play a major role in the preparation and trigger of slope instabilities. However, the interplay with other climatic parameters (in particular precipitation) and the nature of the climate-driven processes that lead to the development of slope instability continue to be poorly understood. This understanding is crucial in order to define reliable scenarios of the evolution of slope instability under the expected climatic and environmental changes. The present work aims to contribute to shed light on these issues by analyzing with the statistical and probabilistic method developed by Paranunzio et al. (2016) the values of the climatic parameters associated to the most significant events of slope instability occurred at high elevation in the Italian Alps in 2016. The method allows to detect the anomalies in temperature and precipitation values that are associated to the development of these slope instabilities, providing the ground for discussion of possible causes and triggering mechanisms, also in the framework of ongoing climate change. Paranunzio R., Laio F., Chiarle M., Nigrelli G., Guzzetti F. (2016) - Climate anomalies associated to the occurrence of rockfalls at high-elevation in the Italian Alps. Natural Hazards and Earth System Sciences, 16, 2085-2106, DOI: 10.5194/nhess-16-2085-2016

An integrated approach to investigate climate-driven rockfall occurrence in high alpine slopes: the Bessanese glacial basin, Western Italian Alps

Rockfalls are one of the most common instability processes in high mountains. They represent a relevant issue, both for the risks they represent for (infra) structures and frequentation, and for their potential role as terrestrial indicators of climate change. This study aims to contribute to the growing topic of the relationship between climate change and slope instability at the basin scale. The selected study area is the Bessanese glacial basin (Western Italian Alps) which, since 2016, has been specifically equipped, monitored and investigated for this purpose. In order to provide a broader context for the interpretation of the recent rockfall events and associated climate conditions, a cross-temporal and integrated approach has been adopted. For this purpose, geomorphological investigations (last 100 years), local climate (last 30 years) and near-surface rock/air temperatures analyses, have been carried out. First research outcomes show that rockfalls occurred in two different geomorphological positions: on rock slopes in permafrost condition, facing from NW to NE and/or along the glacier margins, on rock slopes uncovered by the ice in the last decades. Seasonal thaw of the active layer and/or glacier debutressing can be deemed responsible for slope failure preparation. With regard to timing, almost all dated rock falls occurred in summer. For the July events, initiation may have been caused by a combination of rapid snow melt and enhanced seasonal thaw of the active layer due to anomalous high temperatures, and rainfall. August events are, instead, associated with a significant positive temperature anomaly on the quarterly scale, and they can be ascribed to the rapid and/or in depth thaw of the permafrost active layer. According to our findings, we can expect that in the Bessanese glacierized basin, as in similar high mountain areas, climate change will cause an increase of slope instability in the future. To fasten knowledge deepening, we highlight the need for a growth of a network of high elevation experimental sites at the basin scale, and the definition of shared methodological and measurement standards, that would allow a more rapid and effective comparison of data

Co-design of sectoral climate services based on seasonal prediction information in the Mediterranean

We present in this contribution the varied experiences gathered in the co-design of a sectoral climate services collection, developed in the framework of the MEDSCOPE project, which have in common the application of seasonal predictions for the Mediterranean geographical and climatic region. Although the region is affected by low seasonal predictability limiting the skill of seasonal forecasting systems, which historically has hindered the development of downstream services, the project was originally conceived to exploit windows of opportunity with enhanced skill for developing and evaluating climate services in various sectors with high societal impact in the region: renewable energy, hydrology, and agriculture and forestry. The project also served as the scientific branch of the WMO-led Mediterranean Climate Outlook Forum (MedCOF) that had as objective -among others- partnership strengthening on climate services between providers and users within the Mediterranean region. The diversity of the MEDSCOPE experiences in co-designing shows the wide range of involvement and engagement of users in this process across the Mediterranean region, which benefits from the existing solid and organized MedCOF community of climate services providers and users. A common issue among the services described here -and also among other prototypes developed in the project- was related with the communication of forecasts uncertainty and skill for efficiently informing decision-making in practice. All MEDSCOPE project prototypes make use of an internally developed software package containing process-based methods for synthesising seasonal forecast data, as well as basic and advanced tools for obtaining tailored products. Another challenge assumed by the project refers to the demonstration of the economic, social, and environmental value of predictions provided by these MEDSCOPE prototypes.The work described in this paper has received funding from the MEDSCOPE project co-funded by the European Commission as part of ERA4CS, an ERA-NET initiated by JPI Climate, grant agreement 690462

New insights in the relation between climate and slope failures at high-elevation sites

Climate change is now unequivocal; however, the type and extent of terrestrial impacts are still widely debated. Among these, the effects on slope stability are receiving a growing attention in recent years, both as terrestrial indicators of climate change and implications for hazard assessment. High-elevation areas are particularly suitable for these studies, because of the presence of the cryosphere, which is particularly sensitive to climate. In this paper, we analyze 358 slope failures which occurred in the Italian Alps in the period 2000–2016, at an elevation above 1500 m a.s.l. We use a statistical-based method to detect climate anomalies associated with the occurrence of slope failures, with the aim to catch an eventual climate signal in the preparation and/or triggering of the considered case studies. We first analyze the probability values assumed by 25 climate variables on the occasion of a slope-failure occurrence. We then perform a dimensionality reduction procedure and come out with a set of four most significant and representative climate variables, in particular heavy precipitation and short-term high temperature. Our study highlights that slope failures occur in association with one or more climate anomalies in almost 92% of our case studies. One or more temperature anomalies are detected in association with most case studies, in combination or not with precipitation (47% and 38%, respectively). Summer events prevail, and an increasing role of positive temperature anomalies from spring to winter, and with elevation and failure size, emerges. While not providing a final evidence of the role of climate warming on slope instability increase at high elevation in recent years, the results of our study strengthen this hypothesis, calling for more extensive and in-depth studies on the subject

Changes of the Coastal Zones Due to Climate Change

“Changes of the Coastal Zones Due to Climate Change” explores the complex relationship between coastal climate change and sea dynamics while placing the research within a broader context of climate change and its effects on coastal ecosystems [...

A method to reveal climatic variables triggering slope failures at high elevation

The air temperature in the Alps has increased at a rate more than twice the global average in the last century, and a significant increase in the number of slope failures has also been documented, in particular in glacial and periglacial areas. Thus, the relationship between climatological forcing and processes of instability at high elevation is worth analyzing. We provide a simple, statistically based method aimed at identifying a relationship between climate factors and the triggering of geohazards. Our main idea is to compare the meteorological conditions at the time when the instability occurred with the typical conditions in the same place. Carrying out a straightforward analysis based on the use of the empirical distribution function, we are able to determine whether any of the meteorological variables had nonstandard values in the lead-up to the slope failure event, and thus to identify the variables that are likely to have acted as triggering factors for the slope failure. The method has been tested on five events in the glacial and periglacial areas of the Piedmont Alps (Northwestern Italy) occurring between 1989 and 2008. Out of these five case studies, our research shows that four can be attributed to climatic anomalies (rise of temperature and/or heavy precipitation). The results of this study may contribute to developing knowledge about the relationships between climatic variables and slope failures at high elevations, providing interesting insights into the expected impact of ongoing global warming on geohazards. Keyword

Evaluating the Effects of Urbanization Evolution on Air Temperature Trends Using Nightlight Satellite Data

Confounding factors like urbanization and land-use change could introduce uncertainty to the estimation of global temperature trends related to climate change. In this work, we introduce a new way to investigate the nexus between temporal trends of temperature and urbanization data at the global scale in the period from 1992 to 2013. We analyze air temperature data recorded from more than 5000 weather stations worldwide and nightlight satellite measurements as a proxy for urbanization. By means of a range of statistical methods, our results quantify and outline that the temporal evolution of urbanization affects temperature trends at multiple spatial scales with significant differences at regional and continental scales. A statistically significant agreement in temperature and nightlight trends is detected, especially in low and middle-income regions, where urbanization is rapidly growing. Conversely, in continents such as Europe and North America, increases in temperature trends are typically detected along with non-significant nightlight trends