Abstract. Soil erosion is a major problem around the world because of its effects on soil productivity, nutrient loss, siltation in water bodies, and degradation of water quality. By understanding the driving forces behind soil erosion, we can more easily identify erosion-prone areas within a landscape to address the problem strategically. Soil erosion models have been used to assist in this task. One of the most commonly used soil erosion models is the Universal Soil Loss Equation (USLE) and its family of models: the Revised Universal Soil Loss Equation (RUSLE), the Revised Universal Soil Loss Equation version 2 (RUSLE2), and the Modified Universal Soil Loss Equation (MUSLE). This paper reviews the different sub-factors of USLE and RUSLE, and analyses how different studies around the world have adapted the equations to local conditions. We compiled these studies and equations to serve as a reference for other researchers working with (R)USLE and related approaches. Within each sub-factor section, the strengths and limitations of the different equations are discussed, and guidance is given as to which equations may be most appropriate for particular climate types, spatial resolution, and temporal scale. We investigate some of the limitations of existing (R)USLE formulations, such as uncertainty issues given the simple empirical nature of the model and many of its sub-components; uncertainty issues around data availability; and its inability to account for soil loss from gully erosion, mass wasting events, or predicting potential sediment yields to streams. Recommendations on how to overcome some of the uncertainties associated with the model are given. Several key future directions to refine it are outlined: e.g. incorporating soil loss from other types of soil erosion, estimating soil loss at sub-annual temporal scales, and compiling consistent units for the future literature to reduce confusion and errors caused by mismatching units. The potential of combining (R)USLE with the Compound Topographic Index (CTI) and sediment delivery ratio (SDR) to account for gully erosion and sediment yield to streams respectively is discussed. Overall, the aim of this paper is to review the (R)USLE and its sub-factors, and to elucidate the caveats, limitations, and recommendations for future applications of these soil erosion models. We hope these recommendations will help researchers more robustly apply (R)USLE in a range of geoclimatic regions with varying data availability, and modelling different land cover scenarios at finer spatial and temporal scales (e.g. at the field scale with different cropping options).

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As the linked impacts of climate change and degradation of ecosystems continue to be felt, particularly in developing countries, it is vital that methods for development that concurrently address adaptation to climate change, rapid urbanisation, and ecosystem degradation be explored. Further development of approaches which are participatory and embedded in an understanding of the importance of symbiotic relationships between sociocultural and ecological systems is particularly important. Ecosystem-based adaptation (EbA) is one such method that is gaining recognition and momentum in areas where developing nations face converging pressures and drivers of change. EbA methodologies to date, are often ill-defined in an urban context and lack consideration of future social and ecological scenarios however. In response, this paper describes a methodology for developing urban EbA projects in a small island developing nation context. The methodology was developed and applied by a multi-disciplinary team working under the auspices of the Secretariat of the Pacific Regional Environment Programme (SPREP). The application of this methodology in Port Vila, Vanuatu indicated: i) the needs of local people must be at the forefront of project planning, requiring a participatory design process; ii) EbA solutions development must be multidisciplinary and iterative; iii) appropriate quantitative and qualitative data is vital as a basis for EbA project development, requiring adequate time for data gathering; iv) urban and coastal EbA projects must be developed holistically, recognising socio-ecological systems that extend beyond the urban area itself; v) the complex overlapping landscape of governmental and international aid financed projects must inform the development of new EbA projects; vi) potential monetary and non-monetary benefits, costs and risks across multiple factors must be carefully assessed in EbA project development; and vii) project implementation requires ongoing engagement and a readiness to adapt to on-the-ground realities.

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