Geomorphological records of extreme floods and their relationship to decadal-scale climate change

Extreme rainfall and flood events in steep upland catchments leave geomorphological traces of their occurrence in the form of boulder berms, debris cones, and alluvial fans. Constraining the age of these features is critical to understanding (i) landscape evolution in response to past, present, and future climate changes; and (ii) the magnitude–frequency of extreme, ungauged floods in small upland catchments. This research focuses on the Cambrian Mountains of Wales, UK, where lichenometric dating of geomorphological features and palaeohydrological reconstructions is combined with climatological data and documentary flood records. Our new data from Wales highlight a distinct flood-rich period between 1900 and 1960, similar to many other UK lichen-dated records. However, this study sheds new light on the underlying climatic controls on upland flooding in small catchments. Although floods can occur in any season, their timing is best explained by the Summer North Atlantic Oscillation (SNAO) and shifts between negative (wetter than average conditions with regular cyclonic flow and flooding) and positive phases (drier than average conditions with less frequent cyclonic flow and flooding), which vary from individual summers to decadal and multidecadal periods. Recent wet summer weath-er, flooding, and boulder-berm deposition in the UK (2007–2012) are related to a pronounced negative phase shift of the SNAO. There is also increasing evidence that recent summer weather extremes in the mid-latitudes may be related to Arctic amplification and rapid sea ice loss. If this is the case, continuing and future climate change is likely to mean that (i) unusual weather patterns become more frequent; and (ii) upland UK catchments will experience heightened flood risk and significant geomorphological changes

Searching for an Anthropo(s)cene in the uplands of mid Wales

This essay presents the responses of four creative writers to the highly modified landscapes of the Cambrian Mountains in mid Wales. Through a tour of the historic mine site of Cwmystwyth and the dams of Cwm Elan, our aims were to engage with the concept of the Anthropocene in a landscape that could be emblematic of the proposed new geological interval. Through poems and prose inspired by these landscapes, the physical, social, cultural, and political processes shaping them are explored. The pieces have a strong sense of place, and touch on themes of pollution of the environment by heavy metals, geomorphological impacts of dams, and the human stories associated with those places. We demonstrate the great potential of such places and landscapes as sites where artistic creativity and science can engage and collaborate to find ways of communicating concepts such as the Anthropocene and the anthroposcenic

Incorporating sedimentological data in UK flood frequency estimation

This study presents a new analytical framework for combining historical flood data derived from sedimentological records with instrumental river flow data to increase the reliability of flood risk assessments. Historical flood records were established for two catchments through re-analysis of sedimentological records; the Nant Cwm-du, a small, steep upland catchment in the Cambrian Mountains of Wales, and a piedmont reach of the River Severn in mid Wales. The proposed framework is based on maximum likelihood and least-square estimation methods in combination with a Generalised Logistic distribution; this enables the sedimentological data to be combined effectively with existing instrumental river flow data. The results from this study are compared to results obtained using existing industry standard methods based solely on instrumental data. The comparison shows that inclusion of sedimentological data can have an important impact on flood risk estimates, and that the methods are sensitive to assumptions made in the conversion of the sedimentological records into flood flow data. As current industry standard methods for flood risk analysis are known to be highly uncertain, the ability to include additional evidence of past flood events derived from sedimentological records as demonstrated in this study can have a significant impact on flood risk assessments

Extending the Global Sensitivity Analysis of the SimSphere model in the Context of its Future Exploitation by the Scientific Community

In today’s changing climate, the development of robust, accurate and globally applicable models is imperative for a wider understanding of Earth’s terrestrial biosphere. Moreover, an understanding of the representation, sensitivity and coherence of such models are vital for the operationalisation of any physically based model. A Global Sensitivity Analysis (GSA) was conducted on the SimSphere land biosphere model in which a meta-modelling method adopting Bayesian theory was implemented. Initially, effects of assuming uniform probability distribution functions (PDFs) for the model inputs, when examining sensitivity of key quantities simulated by SimSphere at different output times, were examined. The development of topographic model input parameters (e.g., slope, aspect, and elevation) were derived within a Geographic Information System (GIS) before implementation within the model. The effect of time of the simulation on the sensitivity of previously examined outputs was also analysed. Results showed that simulated outputs were significantly influenced by changes in topographic input parameters, fractional vegetation cover, vegetation height and surface moisture availability in agreement with previous studies. Time of model output simulation had a significant influence on the absolute values of the output variance decomposition, but it did not seem to change the relative importance of each input parameter. Sensitivity Analysis (SA) results of the newly modelled outputs allowed identification of the most responsive model inputs and interactions. Our study presents an important step forward in SimSphere verification given the increasing interest in its use both as an independent modelling and educational tool. Furthermore, this study is very timely given on-going efforts towards the development of operational products based on the synergy of SimSphere with Earth Observation (EO) data. In this context, results also provide additional support for the potential applicability of the assimilation of spatial analysis data derived from GIS and EO data into an accurate modelling framework