The velocity of climate change revisited: Smooth velocity field and ecological relevance
- 1Group of Applied Physics, University of Geneva, Geneva, Switzerland (jerome.kasparian@unige.ch)
- 2Institute for Environmental Sciences, University of Geneva, Geneva, Switzerland
- 3DQMP, University of Geneva, Geneva, Switzerland
Describing climate change in terms of spatial velocity is essential to assess the ability for ecosystems or individual species to migrate at a sufficient pace to keep environmental conditions allowing their survival. While climate models provide a temporal evolution of a number of variables at each point of their computational grid, Loarie et al. introduced a velocity of climate change, defined as the ratio of the temporal derivative to the spatial gradient of temperature, or any other variable such as precipitations [1]. This amounts to assume that isotherms shift along the temperature gradient. Although intuitive, this idea is mathematically correct only for straight isotherms parallel to each other [2]. Whenever this condition is not met, e.g., due to complex topography or coastlines, the gradient-based velocity field will display artefacts in the form of local convergence or divergence that are likely to bias the analysis.
We show that these artefacts can be fixed by defining a much more regular velocity field. This alternative approach to the velocity of climate change determines the direction of the velocity vector by minimising the local vorticity rather than by the gradient. From a fundamental point of view, the resulting smoother velocity field allow an analysis at finer temporal and spatial scales. It also allows to define the climate trajectory of a given origin point. Our approach also provides tools to estimate the stability of climate trajectories depending on the behaviour of their "return" trajectory obtained by reversing time [3].
From an ecological point of view, we discuss preliminary results on the relevance of each definition of the velocity of climate change, based on comparisons of the obtained climate trajectories with ecological trajectories from observational data relative to species distribution areas.
References
1. S. R. Loarie et al., Nature 462, 1052 (2009)
2. J. Rey, G. Rohat, M. Perroud, S. Goyette, J. Kasparian, Env. Res. Lett. 15, 034027 (2020)
3. I. Gaponenko, G. Rohat, S. Goyette, P. Paruch, J. Kasparian, Sci. Rep., 12, 2997, (2022)
How to cite: Kasparian, J., Gaponenko, I., Moinat, L., Rohat, G., Goyette, S., and Paruch, P.: The velocity of climate change revisited: Smooth velocity field and ecological relevance, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3217, https://doi.org/10.5194/egusphere-egu23-3217, 2023.
