Research Physical Scientist
USDA Agricultural Research Service Hydrology and Remote Sensing Laboratory
Beltsville, MD
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.
I completed a PhD at UC Berkeley in 2019 with Professors Sally Thompson and Inez Fung. I received an NSF Earth Sciences Postdoctoral Fellowship in 2020, which supported my work with Professor Gabriel Katul at Duke University how runoff at the timescales of individual storms relates to growth and development of plant communities on yearly to decadal timescales. I was hired as a Category 1 Research Physical Scientist with the USDA-ARS Hydrology and Remote Sensing Laboratory in 2022. The physics of storm runoff in dryland environments is an ongoing focus of my work at USDA-ARS, including the refinement of resistance formulations used to parameterize runoff models. A newer focus area is the development of novel tools to estimate how wind advection from fallowed to irrigated fields enhances evapotranspiration downwind, potentially reducing water savings incurred by fallowing previously irrigated fields.
RESEARCH AREAS
Selected article: Crompton, O. V., & Thompson, S. E. (2021). Sensitivity of dryland vegetation patterns to storm characteristics. Ecohydrology, 14(2), e2269.
Vegetation patterns and dryland vulnerability
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?
Hydrodynamics of overland flow in patchy landscapes
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?
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)
Physically-informed data science: temperature effects of tropical forest loss
Like natural evaporative air conditioners, tropical forests lower surface temperatures, and deforestation-induced surface warming is known to extend beyond deforested zones to undisturbed forests. In tropical countries such as Indonesia, Brazil and the Congo, rapid deforestation may have accounted for up to 75% of the observed surface warming between 1950 and 2010. With more than 40% of the world’s population living in the tropics, keeping forests intact is vital to protect those who live in and around them as the planet warms.
This raises a number of policy-relevant questions: If forest conversion is to take place, it is possible to plan that conversion to have smaller warming effects? Can the cooling provided by intact forest to surrounding farmland help to make a `business case’ for preserving intact forest?
To answer these questions, this research uses satellite data over Indonesia, Malaysia and Papua New Guinea to ask how contextual factors –i.e, the spatial extent of forest loss and its level of fragmentation – influence observed surface warming.
Areas of forest cleared for oil palm plantations, in Bawa village, Indonesia. Indonesia is the world’s largest producer of palm oil. EPA/HOTLI SIMANJUNTAK
Selected article: Crompton, O., Corrêa, D., Duncan, J. A., & Thompson, S. E. (2021). Deforestation-induced surface warming is influenced by the fragmentation and spatial extent of forest loss in Maritime Southeast Asia. Environmental Research Letters
See our article in The Conversation!
Wildfire restoration in the Sierra Nevada mountains
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.
Visuals
2000-2019 forest loss (red) from the Hansen Global Forest Change dataset.