My research focuses on rainfall-driven processes at the Earth’s surface, including overland flow generation, sediment transport, erosion and biogeochemical fluxes with a specific focus on dryland basins – critical regions of the globe where water and nutrients are greatly limited. These marginal environments can undergo significant ecosystem transformations associated with land degradation which may persist for hundreds to thousands of years with important consequences for the sustainability of water and land resources. Drylands and their resources are currently under immense pressure from climate change, periods of drought, anthropogenic activities and conflict and thus present multiple environmental and societal challenges of global significance.   

Hillslope hydrology and sediment transport

The action of running water is undoubtedly one of the most important drivers of landscape change globally which is directly coupled to climate. Hillslope sediment supply to valley floors remains poorly constrained because it is episodic and spatially variable within basins and is controlled by the interplay between hillslope characteristics and climatic forcing. I have been investigating the theoretical relationships between sediment flux and hillslope attributes in runoff-dominated systems and I have developed a numerical model based on first principles which couples rainfall-runoff generation to a sediment transport of mixed sediment sizes which I use to investigate the relationship between rainfall, runoff, hillslope attributes and sediment flux to the slope base and the impact on river channel characteristics. I am particularly interested in modelling and measuring the grain-size distribution of hillslope sediment supplied to the channel and its impact and legacy on channel processes and basin topographic evolution.

Dryland hydrology and geomorphology

I am interested in the way dryland basins respond to rainstorms in the short term and in the way they evolve morphologically in the long-term. I have been exploring the impact of longitudinal hillslope sediment supply (flux and grain size distribution) on fluvial response and bed material grain-size distributions and combining numerical modelling and field investigations to understand the role of hillslope runoff and sediment supply on channel sediment dynamics. My ultimate goal is to develop theory and numerical modelling capability to understand dryland basin evolution in response to climatic changes.

Drivers of dryland degradation

Existing theories on land-degradation dynamics suggest that the long-term and irreversible ecosystem shifts over centennial to millennial timescales result from complex feedbacks that arise between vegetation type, water and sediment transfers, and the associated nutrient fluxes, such that some vegetation communities are able to persist and expand over others. These theories are predicated on the poorly resolved relative roles of runoff and erosion in driving nutrient fluxes from different vegetation types. Using field-based, rainfall-simulation experiments we have been exploring plant-level dynamics of runoff- and erosion-driven nutrient fluxes of N, P and K species. Our results highlight important linkages between physical and biogeochemical processes that are controlled by plant structure. We have determined that the magnitude of sediment-bound nutrient export is determined by the grain-size distribution of the eroded sediment as well as the total amount of sediment eroded. Crucially, we observed that grassland areas consistently export the highest yields of sediment-bound N, P and K despite producing similar erosion rates to shrub and intershrub areas due to the significant enrichment of fines in the eroded sediment. These findings have implications for better understanding how grassland areas are being replaced by shrubs and provide insights into the mechanisms of continuing land degradation in drylands. Currently my group is researching in more detail the changes in N cycling within a degradation gradient in dryland soils and particularly probing the importance of organic N. 

Impacts of war on dryland ecosystems

Contemporary wars are concentrated disproportionately in dryland regions (e.g. Syria, Iraq, Afghanistan, South Sudan, Somalia) yet little is known about their impacts and long-term socio-environmental consequences. The aim of this interdisciplinary work is to understand the direct and indirect impacts of war on dryland environments and establish foundations for building socio-ecological resilience to environmental degradation during- and post-conflict. In my recently funded project we are focusing on Somalia, one of the poorest and least developed countries in the world. Decades of internal conflict have degraded Somalia’s vulnerable dryland environment with deleterious impacts on its people, the majority of whom rely on the land for their livelihoods. We are using interdisciplinary perspectives involving science, social science and humanities to better understand the direct physical impacts of war as well as the changes in human behavior resulting from conflict that indirectly degrade the land.