Comparing ecological relevance of climate velocity indices

Climate change has been shown to induce shifts in species distribution areas. These shifts are
driven not only by climate parameters, but also by short-term weather events, topography and other
non-climate factors. Furthermore, the estimation of magnitude of the climate change velocity requires
assumptions regarding its direction, since the two-dimensional velocity vector is not fully constrained
by temperature, which is a scalar. Furthermore, the definition of the magnitude and direction of the
climate velocity is not univocal; assumptions are needed, based on physical as well as mathematical
arguments. The well-known gradient-based definition of climate change [1] has limitations and in
particular local divergences [2]. This has recently prompted the introduction of an alternative method
that aims to maximise the regularity of the velocity field. This method is known as Monte-Carlo
iTerative Convergence Method (MATCH) [3].
The ecological relevance of these methods for specific purposes necessitates assessment. Here, we
asses them against observed shifts in species distribution ranges. The present study includes both ma-
rine and terrestrial species, including North American birds as determined by the Audubon Christmas
Bird Count and the NOAA fisheries survey along the North American coast. The centroid of each
species distribution range is determined at decade-long time ranges and over the entire survey period.
The shifting velocity of these centroids are computed with respect to the latitudinal, longitudinal
and vertical (respectively elevation and depth) directions. The isotherm shift is calculated using the
gradient-based and the MATCH methods for ground and sea-surface temperatures at each observation
location.
The results obtained demonstrate a significant positive correlation between latitudinal and ver-
tical (depth or height) shifts calculated with the MATCH approach, as evidenced by the analysis of
bird species in the western part of the North American continent and marine species. Conversely, no
correlation was found between longitudinal shifts and climate shifts calculated with either method.
These findings suggests that the MATCH approach generates velocity fields that are more relevant
ecologically. It may help to anticipate species range shifts and adapt conservation strategies accord-
ingly.

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)