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Urban gullies are a rapidly growing concern in many tropical cities of the Global South. Various measures are already implemented for their stabilization. However, an overview of these measures and their overall effectiveness is currently lacking. We aim at addressing this gap by documenting existing initiatives to stabilize urban gullies in D.R. Congo and assessing their overall effectiveness. To this end we conducted extensive field campaigns in Kinshasa, Kikwit and Bukavu and combined our terrain observations with data on gully expansion rates (derived from series of satellite imagery). In total, we characterized present and past stabilization initiatives for 398 urban gullies. For 69 of these gullies, the effect of a specific measure on gully expansion rates could be estimated. Results show that for the large majority of gullies, various measures have been implemented. Yet, these are mainly ad-hoc measures installed by the affected population. More structural measures based on larger engineering works were observed for only 20–30% of gullies. The huge efforts invested in the installation of measures strongly contrast with their overall low impact. Among all strategies, only the deviation of runoff resulted in significantly lower expansion rates after installation. The numerous initiatives that rely on the sparse means available seem to have limited effects. This does not imply, however, that they are completely ineffective and should be abandoned. Based on our findings, we formulate recommendations for further research on how to effectively prevent and stabilize urban gullies, taking into account the difficult environmental and socio-economic context

As a network of researchers we release an open-access database (EUSEDcollab) of water discharge and suspended sediment yield time series records collected in small to medium sized catchments in Europe. EUSEDcollab is compiled to overcome the scarcity of open-access data at relevant spatial scales for studies on runoff, soil loss by water erosion and sediment delivery. Multi-source measurement data from numerous researchers and institutions were harmonised into a common time series and metadata structure. Data reuse is facilitated through accompanying metadata descriptors providing background technical information for each monitoring station setup. Across ten European countries, EUSEDcollab covers over 1600 catchment years of data from 245 catchments at event (11 catchments), daily (22 catchments) and monthly (212 catchments) temporal resolution, and is unique in its focus on small to medium catchment drainage areas (median = 43 km2, min = 0.04 km2, max = 817 km2) with applicability for soil erosion research. We release this database with the aim of uniting people, knowledge and data through the European Union Soil Observatory (EUSO).

Predicting gully erosion at the continental scale is challenging with current generation models. Moreover, datasets reflecting gully erosion processes are still rather scarce, especially in Africa. This study aims to bridge this gap by collecting an extensive dataset and developing a robust, empirical model that predicts gully head density at high resolution for the African continent. We developed a logistic probability model at 30 m resolution that predicts the likelihood of gully head occurrence using currently available GIS data sources. To calibrate and validate this model, we used a new database of 31,531 gully heads, mapped over 1216 sites across Africa. The exact location of all gully heads was manually mapped by trained experts using high-resolution imagery available from Google Earth. This allowed the extraction of detailed information at the gully head scale, such as the local soil surface slope. Variables included in our empirical model are topography, climate, vegetation, soil characteristics and tectonic context. They are consistent with our current process-based understanding of gully formation and evolution. The model shows that gully occurrences mainly depend on slope steepness, soil texture and vegetation cover and to a lesser extent on rainfall intensity and tectonic activity. The combination of these factors allows for robust and fairly reliable predictions of gully head occurrences, with Areas Under the Curve for validation around 0.8. Based on these results, we present the first gully head susceptibility map for Africa at a 30 m resolution.

The quantification and monitoring of soil organic carbon (SOC) in croplands is crucial in a context of effective and precise agricultural management. Conventional methods to assess SOC changes pose some limitations on time and labor consumption to efficiently assess SOC distributions and dynamics in a spatial and temporal context. Recent developments in Uncrewed Aircraft Systems (UAS), combined with miniaturized visible-near infrared sensors bring opportunities for the rapid and low-cost field-scale SOC mapping. It shows the potential of UAS-soil sensing to bridge the gap between high-resolution plot-scale sensing at centimetre-level and moderate-resolution landscape-scale sensing at meter-level from airborne or satellite platforms. For the UAS sensing system, variety of sensor types enable the multiple dimensional monitoring (i.e., temporal, spatial and spectral) of soil properties, while it brings large uncertainties in choosing a desirable sensor specification for a monitoring purpose. Accordingly, it lacks a capability evaluation for different sensor types in the estimation of soil properties. Meanwhile, there is still room for improving the pre-processing approaches against the perturbing factors such as soil roughness and anisotropy. A comprehensive understanding of how these perturbing factors affecting soil reflectance spectra under different measurement conditions will assist in the use of SOC prediction models derived from an existing regional soil spectral library (SSL), which can be applied to UAS-based hyperspectral data to reduce the need for additional field sampling. The overall aim of this thesis was therefore to improve the spatial and spectral accuracy and effectiveness of UAS-based multi- and hyper-spectral measurement for the estimation of SOC content in croplands. In this thesis, we started with assessing the potential of a non-imaging spectrometer on UAS-borne SOC estimation. We showed that local calibration with soil sampling had good capabil, (SC - Sciences) -- UCL, 2022