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.