T. C. Hill's research while affiliated with The University of Edinburgh and other places

Publications (13)

Article
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Background: The success of satellites in mapping deforestation has been invaluable for improving our understanding of the impacts and nature of land cover change and carbon balance. However, current satellite approaches struggle to quantify the intensity of forest disturbance, i.e. whether the average rate of biomass loss for a region arises from...
Article
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Carbon emissions from tropical land‐use change are a major uncertainty in the global carbon cycle. In African woodlands, small‐scale farming and the need for fuel are thought to be reducing vegetation carbon stocks, but quantification of these processes is hindered by the limitations of optical remote sensing and a lack of ground data. Here, we pre...
Article
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The planetary boundary layer (PBL) provides an important link between the scales and processes resolved by global atmospheric sampling/modeling and site-based flux measurements. The PBL is in direct contact with the land surface, both driving and responding to ecosystem processes. Measurements within the PBL (e.g., by radiosondes, aircraft profiles...
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We present an approach for dealing with coarse-resolution Earth observations (EO) in terrestrial ecosystem data assimilation schemes. The use of coarse-scale observations in ecological data assimilation schemes is complicated by spatial heterogeneity and nonlinear processes in natural ecosystems. If these complications are not appropriately dealt w...
Article
The Arctic has already warmed significantly, and warming of 4-7 °C is expected over the next century. However, linkages between climate, the carbon cycle, the energy balance, and hydrology mean that the response of arctic ecosystems to these changes remains poorly understood. The release by warming of considerable but poorly quantified carbon store...
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Terrestrial carbon sinks are currently believed to account for the removal and storage of approximately 25% of anthropogenic carbon emissions from the atmosphere. The processes involved are numerous and complex and many feedbacks are at play. The ability to study the dynamics of different ecosystems at scales meaningful to climatic forcing is essen...
Article
It is critical to understand the dynamics of ecosystem carbon uptake through seasonal changes and in response to environmental drivers. In this study we utilised aircraft based remote sensing and CO2/H2O flux monitoring systems to quantify changes in photosynthesis along an Arctic transect. The University of Edinburgh's (UK) research aircraft (a Di...
Article
The assimilation of terrestrial carbon, water and nutrient cycle measurements into land surface models of these processes is fundamental to improving our ability to predict how these ecosystems may respond to climate change. A combination of measurements and models, each with their own systematic biases, must be considered when constraining the non...
Article
Arctic ecosystems are responding rapidly to observed climate change. Quantifying the magnitude of these changes, and their implications for the climate system, requires observations of their current structure and function, as well as extrapolation and modelling (i.e. ‘upscaling’) across time and space. Here, we describe the major results of the Int...
Article
Full-text available
The atmosphere and biosphere interact strongly in the planetary boundary layer. Understanding the mechanisms controlling the coupled atmosphere-biosphere system allows improved scaling between observations at the stand scale (e.g., flux towers) and those at larger scales, e.g., airborne or satellite measurements. Simulation of the joint atmosphere-...

Citations

... The quantification of a disturbance's impact on biophysical variables such as changes in biomass, basal area, and height would require accurate reference data from pre-and post-disturbance events. Following the concept that harvest intensity can be estimated as changes in basal area and canopy cover (Healey et al., 2006;Hill et al., 2015), Tao et al. (2019) demonstrated the feasibility of combining Landsat time series and multi-temporal field measurements to quantify disturbance intensity in North and South Carolina for over 30 years. Here disturbance intensity, measured by changes in basal area, is a combination of both natural disturbance severity and anthropogenic activity intensity (e.g., logging intensity). ...
... The Soil-Plant-Atmosphere model (SPA; Williams et al., 1996Williams et al., , 2001a) is a high vertical resolution point model (up to 10 canopy layers and 20 soil layers) which simulates exchanges of carbon, water, and energy between the land surface and atmosphere on 30-minute timesteps. The SPA model has been used for a variety of applications including site level analyses of carbon and water fluxes (Ruehr et al., 2014;Williams et al., 1996;Williams, Law, et al., 2001a, Williams, Rastetter, et al., 2001b; model intercomparisons of stomatal and hydraulic functioning (Bonan et al., 2014;Misson et al., 2004); data assimilation (Sus et al., 2014;Williams et al., 2005); and modeling land-atmosphere feedbacks (Hill et al., 2008;Smallman et al., 2013). In this study, we implemented several model updates including those from a recent study which used the SPA model to simulate the carbon cycle at US-Me2 under current and future climate conditions (Ruehr et al., 2014). ...
... A detailed understanding how canopy height changes at a certain scale related to biomass changes can allow for a direct quantification of the net forest carbon changes from remote sensing (Hiltner et al., 2022;Knapp et al., 2018b). Knowledge about the scaling of forest attribute distributions is also required for downscaling of gridded maps (i.e., super-resolution), for purposes such as data assimilation (Hill et al., 2011;Rödig et al., 2017) or pixel-to-point comparisons between models and field data (Rammig et al., 2018). ...
... Mitchard et al. (2011) was able to detect deforestation and woody encroachment along forest--savanna ecotone of central Cameroon by comparing Advanced Land Observing Satellite (ALOS) Phased Arrayed L-band Synthetic Aperture Radar (PALSAR) data with L-band JERS-1 data acquired 11 years before. Ryan et al., 2012 detected land cover change and quantified the carbon stock losses of 11-33 MgC/ha in Mozambique woodlands using ALOS PALSAR data over a three-year period. Mitchard et al., 2013 detected increases in woodland carbon of 1.1 MgC/ha/year and decreases of 3 MgC/ha/year in Mozambique with ALOS PALSAR, but highlighted the need for more rigorous quantification of uncertainty. ...
... While NEE values are generally similar between chamber and EC methods, differences are attributed to the scale of the measurements (Stoy et al., 2013). Fox et al. (2008) showed that there was large bias in upscaling chamber measurements, relative to EC values in a tundra ecosystem, due to microscale surface heterogeneity of the landscape. ...
... We used ψ l min = −2 MPa, which reflects values typically found in closed forest canopies. This is similar to values used in previous SPA simulations for arctic ecosystems and black spruce boreal forest (−1.5 MPa; Williams et al., 2000;Hill et al., 2011), ponderosa pine (−1.7 to −2.0 MPa; Williams et al., 2001a, b;Schwarz et al., 2004), deciduous forest (−2.5 MPa; Williams et al., 1996), tropical rainforest (−2.5 MPa; Williams et al., 1998;Fisher et al., 2007), and Australian woodland (−2.8 MPa; Zeppel et al., 2008). Overview of the main processes in the canopy model. ...