Dr Anna Harper
My interests include reducing climate change uncertainty through a better understanding of the terrestrial sources and sinks of CO2. I use the land surface model, JULES, to better constrain environmental and physiological controls on photosynthesis, respiration, and transpiration. Each of these processes also have important implications for and feedbacks to the climate system. I am particularly interested in the Amazon rainforest, an amazing ecosystem which provides invaluable services to humanity - not least of which is the capture and storage of CO2. Drought threatens this ecosystem. How the forest responds to droughts and the likelihood of future droughts will both play large roles in the future of the global carbon cycle and climate. Below is further description of some projects I am working on.
Plants "eat" CO2 to live, so to first order vegetation will benefit from growing atmospheric CO2 concentrations. BUT there are several complicating factors which in reality will control how much extra CO2 plants can assimilate: changes in weather and climate patterns, changes in nutrient availability, and human land use change and degradation. I'm involved in a project to better understand how plants will respond to rising CO2 using "FACE" (free-air enrichment of CO2) experiments. During these experiments, extra CO2 is pumped into a study area and the responses of the plants and soils are measured. My role is to use JULES to see which processes might be most important in the real world that are missing in earth system models.
The global carbon budget:
Simulations by Andy Wiltshire (UK Met Office) and I using the JULES land surface model contributed to the 2013 global carbon budget, read the summary here: http://www.metoffice.gov.uk/research/news/gcb-2013
Plant trait-climate interactions
An important question with climate change is how will terrestrial storage of CO2 be affected? If climate change reduces the CO2 stored on land, there will be a positive feedback as more CO2 will go into the air and cause further climate change. Therefore it's essential to get a better grasp on what will happen to vegetation with climate change.
Trees invest in leaf nutrients and structure, and this can determine their long-term viability in a climate regime. For example, deciduous trees tend to have thin leaves with high nutrient concentrations - the leaves aren't on the tree for long so they need to assimilate as much carbon dioxide as possible in their short lifespan. On the other hand, evergreen trees have thick leaves that are in it "for the long haul" - they have low CO2 assimilation rates but over their long lifespans they can bring in loads of CO2. These investment strategies can vary with climate and that is the motivation for current research I am involved in with Professor Stephen Sitch (in Geography), and Dr. Peter van Bodegom and Lieneke Verheijen in the Netherlands.
Recent Publications (please e-mail me if you would like a copy but do not have access to a journal)
JM Osborne, FH Lambert, AB Haprer, M Groenendijk, S Sitch, CD Koven, B Poulter, TAM Pugh, BD Stocker, A Wiltshire, S Zaehle (2015), Reconciling precipitation with runoff: observed hydrological changes in mid-latitudes. Journal of Hydrometeorology.
P Good, AB Harper, A Meesters, E Robertson, R Betts (2015), Are strong fire-vegetation feedbacks needed to explain the spatial distribution of tropical tree cover? Accepted to Global Ecology and Biogeography.
A Anav, P Friedlingstein, C Beer, P Ciais, A Harper, C Jones, G Murray-Tortarolo, D Papale, NC Parazoo, P Peylin, S Piao, S Sitch, N Viovy, A Wiltshire, M Zhao (2015): Spatio-temporal patterns of terrestrial gross primary production: A Review. Review of Geophysics.
G Murray-Tortarolo, P Friendlingstein, S Sitch, VJ Jaramillo, F Murguia-Flores, A Anav, Y Liu, A Arneth, A Arvanitis, AB Harper, A Jain, E Kato, C Koven, B Poulter, BD Stocker, A Wiltshire, S Zaehle, N Zeng (2015): The carbon cycle in Mexico: past, present, and future of C stocks and fluxes. Biogeosciences Discussions.
NC Parazoo, E Barnes, J Worden, AB Harper, KW Bowman, C Frankenberg, S Wolf, M Litvak, TF Keenan (2015): Influence of ENSO and the NAO on terrestrial carbon uptake in the Texax-northern Mexico region. Global Biogeochemical Cycles.
Rowland, L., AB Harper, B. O. Christoffersen, D. R. Galbraith, H. M. A. Imbuzeiro, T. L. Powell, C. Doughty, N. M. Levine, Y. Malhi, S. R. Saleska, P. R. Moorcroft, P. Meir, and M. Williams, (2015) Modelling climate change responses in tropical forests: similar productivity estimates across five models, but different mechanisms and responses. Geoscientific Model Development.
AB Harper, IT Baker, AS Denning, DA Randall, D Dazlich, M Branson, (2014) Impact of evapotranspiration on dry season climate in the Amazon forest. Journal of Climate.
- Press release: http://www.exeter.ac.uk/news/featurednews/title_334187_en.html
IT Baker, AB Harper, HR Rocha, AS Denning, AC Araujo, LS Borma, HC Freitas, ML Goulden, AO Manzi, SD Miller, AD Nobre, N Restrepo-Coupe, SR Saleska, R Stockli, C Randow, SC Wofsy (2013), Surface ecophysiological behavior across vegetation and moisture gradients in tropical South America. Agricultural and Forest Meteorology.
TL Powell, DR Galbraith, BO Christoffersen, AB Harper, HMA Imbuzeiro, L Rowland, S Almeida, PM Brando, ACL da Costa, MH Costa, NM Levine, Y Malhi, SR Saleska, E Sotta, M Williams, P Meir, PR Moorcroft (2013), Confronting model predictions of carbon fluxes with measurements of Amazon forests subjected to experimental drought. New Phytologist.
AB Harper, AS Denning, IT Baker, MD Branson, L Prihodko, DA Randall (2010), Role of deep soil moisture in modulating climate in the Amazon forest. Geophysical Research Letters.