Ecosystem disturbance – from climate and socio-economic pressures – is changing the Earth’s surface at an unprecedented pace, and understanding these impacts is critical for sustainable water resource management.  The need for sustainable resource management calls for a deeper understanding of ecosystem responses to disturbance, and the conditions under which interventions are effective.  My research integrates remote sensing and modeling approaches to examine  the impacts of disturbancesm such as drought, wildfire, deforestation and fragmentation, on water resources.  For research topics spanning wildfire restoration in California to deforestation-induced surface warming,  my research contributes to the evidence base for nature based climate solutions that support local ecosystem function and communities.  

Drylands – including arid and semiarid regions –make up 40% of the earth's land surface and support some 2 billion people.  As the climate warms, these regions are increasingly vulnerable to land degradation and desertification.

Ecology and hydrology are tightly coupled in these water-limited landscapes – storms generate overland flow, which redistributes water from bare soil to vegetated areas, providing additional inputs that sustain vegetation.   Land degradation may flip the hydrology from resource capturing to resource shedding, where overland flow remove water and resources from the landscape. 

To study dryland degradation from a hydrodynamic perspective,  my research uses hydrological models to study  how overland flow mediates threshold-like behaviour between capturing and shedding states.   For example, how can readily available information about vegetation patterns and storm climatology be used to assess ecosystem productivity and health?   

Describing resistance to overland flow in drylands is challenging because these flows traverse complex terrain with spatially varying  surface roughness and infiltration rates.  For example, infiltration rates are  typically low in bare-ground areas due to the formation of surface crusts and higher under vegetation due to root activity and protection of the soil surface against rain-splash by the canopy.  

While a lot is known about flow resistance through vegetation canopies in channel flow settings,  storm runoff in drylands is different: (i) bed resistance cannot be neglected for the very shallow flows generated by storm runoff, and (ii) spatial patterns in roughness and infiltration rates between vegetated and bare soil areas means that effective resistance observed at hillslope scales differs from local flow resistance.

My research addresses fundamental questions about overland flow in patchily vegetated environments:    Can easily observable data – such as a hillslope hydrograph – be inverted  to infer the partitioning of resistance between canopy drag and bed shear stress?  How do contrasts in resistance and permeability between bare soil and vegetated areas influence the resulting flow?    Under what conditions does the greater resistance provided by vegetation versus the contrast in infiltration rates control the flow dynamics?  

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Selected article:  Crompton, O., Katul, G. G., & Thompson, S. (2020). Resistance formulations in shallow overland flow along a hillslope covered with patchy vegetation. Water Resources Research, 56(5)

Devastating fire seasons have become a new normal in California,  due in part to the lack of preventative measures like low-intensity fuel removal controlled burns, lack of thinning, and a long-term history of fire suppression. Worldwide, fire severity and extent are increasing, due to climate change.  The use of managed wildfire to reduce these hazards is a globally relevant strategy for forest management.  The implications of manipulating or restoring forest fire regimes, however, are challenging to determine because of the scarcity of sites subject to long-term fire regime restoration.  Natural wildfire has been restored to only a handful of areas in the Sierra Nevada, and the long term consequences of this restoration are not fully understood.  

This research synthesises long-term research conducted in the Illilouette Creek Basin (ICB) and Sugarloaf Creek Basin (SCB), where fire restoration was implemented in the late 1960s/early 1970s.   To examine the long term consequences of this restoration, I used a simple dynamical model to explore the forest cover dynamics for these basins, finding that forest cover has not yet reached steady state in ICB.

Selected article:  Crompton, O., Boisrame, G., Rakhmatulina, E., Stephens, S., & Thompson, S. (2022). Fire return intervals explain different vegetation cover responses to wildfire restoration in two Sierra Nevada basins. Forest Ecology and Management, 521, 120429.