Simone Fatichi - Variability in annual precipitation and ecohydrological responses

Event type: 
28 February 2018
2.00 - 3.00pm

Climate Change Research Centre, Seminar Room, Mathews Building 4th floor, UNSW, Sydney

Simone Fatichi
Institute of Environmental Engineering, ETH Zurich, Zurich, Switzerland
Climate Change Research Centre, UNSW, Australia

Variability in annual precipitation can affect the hydrological cycle and vegetation productivity. We investigate the effects of interannual variability of precipitation in a number of ecohydrological variables such as evapotranspiration (ET) and above-ground net primary production (ANPP) using the mechanistic ecosystem model T&C. Simulations are performed in a number of locations characterized by different vegetation cover and climate conditions and having at least 10 years of hourly meteorological observations. Additional long-term simulations with meteorological forcing (200 years) generated by means of a weather generator are also performed to provide robust statistical analyses in a few sites. Model results highlight that while cross-site response to changes in average precipitation is rather predictable, a considerable scatter is detected in the relations between annual precipitation and vegetation productivity at single sites, even in water-limited locations. This outcome suggests that controls different from annual precipitation affect interannual variability of ANPP and to a lesser extent ET. Specifically, the occurrence of short periods of favorable conditions, associated with the “most active hours” of ET or vegetation activity is a better explanatory variable for annual ET and carbon fluxes than average annual or growing season conditions. Modeling results on the importance of the “most active hours” are largely confirmed by flux-tower observations.

We further show a double asymmetry of the response of ANPP to annual rainfall. In most locations, variations within ± 1 standard deviation from the mean are characterized by a larger response to rainfall increase rather than decrease (positive asymmetry). For deviations beyond 1 standard deviation from the rainfall mean, we find a dominance of negative asymmetry (larger response to a decrease rather than increase), even though these patterns are associated with large uncertainties and exhibit considerable differences across sites.

As local, single-site (temporal) sensitivities are considerably smaller than the sensitivities observed across (spatial) gradients, they need to be analyzed with caution because of the inherent uncertainties and because factors controlling short-term ANPP and ET variability are considerably different from those controlling spatial and long-term variability.


Speaker Biography: Simone Fatichi is Research Associate and Lecturer at the Institute of Environmental Engineering at ETH Zurich since 2011. He received his BSc and MSc (cum laude) in Earth and Environmental Engineering at the University of Firenze (Italy) and he owns an International PhD title joint between the T.U. Braunschweig (Germany) and University of Firenze (Italy). His areas of expertise are soil-water-plant interactions, biogeosciences, hydrology, and analysis of climate change effects. His research covers a variety of topics and techniques including distributed ecohydrologic modeling, ecosystem modeling, modeling of processes of plant physiology and soil biogeochemistry, methods of stochastic hydrometeorology, and downscaling techniques to study climate change impacts. Recent research efforts have been devoted to the understanding of global change and its implications on water resources, ecosystems, and the carbon cycle. He was recipient of the Torricelli award in 2014.