Unravelling earth flow dynamics with 3-D time series derived from UAV-SfM models

Accurately assessing geo-hazards and quantifying landslide risks in mountainous environments are gaining importance in the context of the ongoing global warming. For an in-depth understanding of slope failure mechanisms, accurate monitoring of the mass movement topography at high spatial and temporal resolutions remains essential. The choice of the acquisition framework for high-resolution topographic reconstructions will mainly result from the trade-off between the spatial resolution needed and the extent of the study area. Recent advances in the development of unmanned aerial vehicle (UAV)-based image acquisition combined with the structure-from-motion (SfM) algorithm for three-dimensional (3-D) reconstruction make the UAV-SfM frame- work a competitive alternative to other high-resolution topographic techniques. In this study, we aim at gaining in-depth knowledge of the Schimbrig earthflow located in the foothills of the Central Swiss Alps by monitoring ground surface displacements at very high spatial and temporal resolution using the efficiency of the UAV-SfM framework. We produced distinct topographic datasets for three acquisition dates between 2013 and 2015 in order to conduct a comprehensive 3-D analysis of the landslide. Therefore, we computed (1) the sediment budget of the hillslope, and (2) the horizontal and (3) the three-dimensional surface displacements. The multitemporal UAV-SfM based topographic reconstructions allowed us to quantify rates of sediment redistribution and surface movements. Our data show that the Schimbrig earthflow is very active, with mean annual horizontal displacement ranging between 6 and 9 m. Combination and careful interpretation of high-resolution topographic analyses reveal the internal mechanisms of the earthflow and its complex rotational structure. In addition to variation in horizontal surface movements through time, we interestingly showed that the configuration of nested rotational units changes through time. Although there are major changes in the in- ternal structure of the earthflow in the 2013–2015 period, the sediment budget of the drainage basin is nearly in equilibrium. As a consequence, our data show that the time lag between sediment mobilization by landslides and enhanced sediment fluxes in the river network can be considerable

Mountains of our future Earth: Defining priorities for mountain research

The Perth conferences, held every 5 years in Perth, Scotland, bring together people who identify as mountain researchers and who are interested in issues related to global change in mountain social-ecological systems. These conferences provide an opportunity to evaluate the evolution of research directions within the mountain research community, as well as to identify research priorities. The Future Earth Strategic Research Agenda provides a useful framework for evaluating the mountain research community\u27s progress toward addressing global change and sustainability challenges. Using a process originally set up to analyze contributions to the 2010 conference, the abstracts accepted for the 2015 conference in the context of the Future Earth framework were analyzed. This revealed a continued geographic underrepresentation in mountain research of Africa, Latin America, and South and Southeast Asia but a more even treatment of biophysical and social science themes than in 2010. It also showed that the Perth conference research community strongly focused on understanding system processes (the Dynamic Planet theme of the Future Earth research agenda). Despite the continued bias of conference contributions toward traditional observation- and conservation-oriented research, survey results indicate that conference participants clearly believe that transdisciplinary, transformative research is relevant to mountains. Of the 8 Future Earth focal challenges, those related to safeguarding natural assets, promoting sustainable land use, increasing resilience and understanding the water-energy-food nexus received considerable attention. The challenges related to sustainable consumption, decarbonizing socioeconomic systems, cities, and health were considerably less well represented, despite their relevance to mountain socioeconomic systems. Based on these findings, we outline a proposal for the future directions of mountain research

Peat soil thickness and carbon storage in the Belgian High Fens: insights from multi-sensor UAV remote sensing

editorial reviewedPeatlands are known to store a large amount of carbon, but global warming and associated changes in hydrology have the potential to accelerate peatland carbon emissions. An in-depth understanding of carbon dynamics within these peatlands is therefore important. However, peatlands are complex ecosystems, and acquiring accurate and reliable estimates of how much carbon is stored underneath the Earth&#8217;s surface is inherently challenging even at small scales. Here, Unmanned Aerial Vehicles (UAVs) equipped with RGB, multispectral, thermal infrared, and LiDAR sensors were combined with Ground Penetrating Radar (GPR) technology and traditional field surveys, to provide a comprehensive 4D monitoring of a peatland landscape in the Belgian High Fens. Data was collected along a hillslope-floodplain transition. We aimed to establish links between the above- and below-ground factors that control soil carbon status, identify the key drivers of carbon storage as well as explore the potential of UAV remote sensing for spatial mapping of peat depth and carbon stock. Our results indicated that peat thickness widely varied (0.2 to 2.1 m) at small scales and is negatively correlated with elevation (r= -0.39, p<0.001). We found that soil organic carbon (SOC) stock is spatially organized, as abundant carbon was observed at the summit and shoulder of the hill, with an average storage of 670.93 &#177; 108.86 t/ha and 601.47 &#177; 133.40 t/ha, respectively. Moreover, the carbon storage exhibited heterogeneity under different vegetation types, with trees having the highest mean SOC stocks at 722.21 &#177; 37.92 t/ha. Through multiple linear regression, we identified 6 environmental variables that can explain 71.44% of SOC stock variance. Clay content is the most critical factor, accounting for nearly 40% of the variance, followed by topography. Contributions from land surface temperature and vegetation remain below 10%. In addition, UAV data provided accurate estimations of both peat depth and SOC stock, with RMSE and R2 values of 0.13 m and 0.88 for the peat depth test dataset, and 114.42 t/ha and 0.84 for the SOC stock. Our study bridged the gap between surface observations and the hidden carbon reservoir below, this not only allows us to improve our ability to assess the spatial distribution of C stocks but also contributes to our understanding of the drivers of C turnover in these highly heterogeneous landscapes, providing insights for environmental science and climate projections

The effect of natural infrastructure on water erosion mitigation in the Andes

The Andes Mountains stretch over about 8900 km and cross tropical, subtropical, temperate and arid latitudes. Very few, if any, of the diverse physiographic, climatic and biogeographic regions in the Andes have been preserved from human impact. Land use and management have significantly altered the magnitude and frequency of erosion events: deforestation and agricultural practices (such as soil tillage and cattle grazing) have modified erosion rates, river sediment loads and landslide occurrences. There is an urgent need to identify which soil conservation and management practices are most effective to combat soil erosion and to mitigate the on-site and off-site effects in the Andean region. Three large groups of water-related interventions can be identified: interventions based on land use and protective land cover including (1) restoration and protection of native ecosystems, such as montane forests or grasslands and (2) forestation with native or exotic species and (3) soil and water conservation measures including crop management, conservation tillage and slow-forming terraces and the implementation of linear elements such as vegetation strips and check dams. To expand the knowledge base on natural infrastructure for erosion mitigation in the Andes, it is necessary to move beyond case-by-case empirical studies to comprehensive assessments. This study reviews the state of evidence on the effectiveness of interventions to mitigate soil erosion by water and is based on Andean case studies. Based on a systematic review of peer-reviewed and grey literature involving more than 120 local case-studies from the Andes, this study addressed the following research questions: (1) Which erosion indicators allow us to assess the effectiveness of natural infrastructure? (2) What is the overall impact of working with natural infrastructure on onsite and off-site erosion mitigation? (3) Which locations and types of studies are needed to fill critical gaps in knowledge and research? From the suite of physical, chemical and biological indicators commonly used in soil erosion research, two indicators were particularly relevant: soil organic carbon of topsoil and soil loss rates at plot scale. The protection and conservation of natural vegetation has the strongest effect on soil quality, with 3.01 ± 0.893 times higher soil organic carbon content in the topsoil compared to control sites. Soil quality improvements are significant but lower for forestation and soil and water conservation measures. Soil and water conservation measures reduce soil erosion to 62.1 ± 9.2 %, even though erosion mitigation is highest when natural vegetation is maintained. The systematic review of the existing literature allowed us to identify critical gaps in knowledge and research. There is a need for future empirical work on soil quality, erosion and sediment yield before/after interventions in data-scarce regions, such as high elevations, regions with either low or high relief, and low to very low or very high precipitation. Besides, most erosion assessments are based on short-term measurements that tend to miss the impact of rare high-magnitude events. Further research is needed to evaluate whether the reported effectiveness holds during extreme events related to, for example, El Niño–Southern Oscillation