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Abstract:
Climate extremes can affect the functioning of terrestrial ecosystems, for instance via
a reduction of the photosynthetic capacity or alterations of respiratory processes. Yet
the dominant regional and seasonal effects of hydrometeorological extremes are still
5 not well documented. Here we quantify and characterize the role of large spatiotemporal
extreme events in gross primary production (GPP) as triggers of continental anomalies.
We also investigate seasonal dynamics of extreme impacts on continental GPP
anomalies. We find that the 50 largest positive (increase in uptake) and negative extremes
(decrease in uptake) on each continent can explain most of the continental
10 variation in GPP, which is in line with previous results obtained at the global scale.
We show that negative extremes are larger than positive ones and demonstrate that
this asymmetry is particularly strong in South America and Europe. Most extremes in
GPP start in early summer. Our analysis indicates that the overall impacts and the
spatial extents of GPP extremes are power law distributed with exponents that vary
15 little across continents. Moreover, we show that on all continents and for all data sets
the spatial extents play a more important role than durations or maximal GPP anomaly
when it comes to the overall impact of GPP extremes. An analysis of possible causes
implies that across continents most extremes in GPP can best be explained by water
scarcity rather than by extreme temperatures. However, for Europe, South America
20 and Oceania we identify also fire as an important driver. Our findings are consistent
with remote sensing products. An independent validation against a literature survey on specific extreme events supports our results to a large extent.
