Land-Atmosphere Cascade Fueled the 2020 Siberian Heatwave

International audienceA heatwave in Siberia starting in January 2020, initiated by a wave 5 pattern in the jet stream, caused the surface air temperature to reach 38°C in June with important impacts on ecosystems and water resources. Here we show that this dynamical setup started a chain of events leading to this long-lasting and unusual event: positive temperature anomalies over Siberia caused early snowmelt, leading to substantial earlier vegetation greening accompanied by decreased soil moisture and browning in the summer. This soil moisture depletion and vegetation browning, in turn, increased the impact of the heatwave on the atmosphere through a land-atmosphere feedback. This line of evidence suggests that large-scale dynamics and land-atmosphere interactions both contributed to the magnitude and persistence of this record-breaking heatwave, in addition to the background global warming impact on mean temperature. Here, we describe a carry-over effect in Siberia from a spring positive temperature anomaly into summer dryness and browning, with retroaction into the atmosphere. With the Arctic warming twice as fast as the global average, this event foreshadows the future of northern latitude continents and emphasizes the importance of both atmospheric dynamics and land-atmosphere interactions in the future as the climate changes. More frequent similar events could have major consequences on the carbon cycle in these carbon-rich northern latitude regions