Impact of climate warming on phenological asynchrony at the
European scale
Our model simulations predict that uniform warming by +4°C will advance
OAB and TDM by similar median values of 19 and 24 days, respectively.
Yet, the variability in the response of OAB and TDM to warming differs.
While the advancement of OAB with warming varies substantially between
geographic locations and lake types
(20th-80th percentiles 0-35 days;
Fig. 3a-d; Fig. S5), the advancement of TDM is spatially more uniform
and considerably less variable between lake types
(20th-80th percentiles 19-30 days;
Fig. 3e-h; Fig. S6). Consequently, the net effect of warming on
phenological asynchrony (PLD) is on average close to zero (median -3
days), but can range from -60 to +60 days (Fig. 3i-l; Fig. 4b; Fig. S7).
How phenological asynchrony (expressed as PLD) changes with warming
depends on the dominant process controlling OAB (Fig. 4a, b) and thus on
lake type and geographic location, because these properties determine
which process controls OAB before and after warming (Fig. 3i-p; Fig.
S7-S9). In northern, eastern, or high-elevation lakes with optical depth
≤ 6, where OAB is controlled by ice-off (Fig. 3m; Fig. S8), asynchrony
will increase because OAB advances more with warming than TDM (Fig.
4a-f; Fig. S9). In contrast, in low-elevation, southern and western
lakes with optical depth 6-18, where OAB is controlled by incident
radiation (Fig. 3n, o; Fig. S8), asynchrony will decrease because only
TDM advances with warming (Fig. 4a-f; Fig. S9). In lakes with optical
depth ≥ 36, where OAB is controlled by the onset of stratification (Fig.
3p, Fig. S8), asynchrony will not change systematically because OAB and
TDM advance similarly with warming (Fig. 4a-f; Fig. S9). Finally, lakes
in which the dominant process controlling OAB will shift with warming –
either from ice-cover to radiation (optical depth 6-12) or from
radiation to stratification (optical depth 24-30) – OAB will advance at
a slightly faster or slower pace than TDM, respectively, leading to
intermediate shifts in asynchrony (Fig. 4a-b, Fig. S9). Intriguingly,
warming will thus decrease asynchrony in lakes in which it is currently
largest (radiation controlled lakes), but will not change asynchrony in
lakes in which it is currently shortest (stratification controlled
lakes; Fig. 4b; Fig. S9).
Overall, the OAB controlling factors explain more than 60% of the
variance in the warming-induced changes in both OAB and PLD in the 16
lake types across Europe (Fig. 4g, i). The controlling factors thus
describe the impact of warming on phenological asynchrony equally well
as does the combination of geographic coordinates and optical depth
(Fig. 4g, i).