Abstract
The devastating North China drought in the summer of 2015 was roughly captured by a dynamical seasonal climate forecast model with a good prediction of the 2015/16 big El Niño. This raises a question of whether strong El Niños imply higher predictability of extreme droughts. Here we show that a strong El Niño does not necessarily result in an extreme drought, but it depends on whether the El Niño evolves synergistically with Eurasian spring snow cover reduction to trigger a positive summer Eurasian teleconnection (EU) pattern that favors anomalous northerly and air sinking over North China. The dynamical forecast model that only well represents the El Niño underpredicts the drought severity, while a dynamical-statistical forecasting approach that combines both the low- and high-latitudes precursors is more skillful at long lead. In a warming future, the vanishing cryosphere should be better understood to improve predictability of extreme droughts.
Highlights
Since the ocean-atmosphere coupled general circulation models (CGCMs) that make use of oceanic memory (e.g., El Niño Sea surface temperature (SST) anomaly) for seasonal forecasting have been widely used to provide drought early warning[23,24,25], it is essential to understand whether a strong El Niño indicates a higher predictability of extreme summer drought in North China
Such Eurasian teleconnection (EU) pattern resulted in anomalous northerlies between the high- and low-pressure centers over North China, weakened the EASM, and thereby reduced the moisture transported from the south
We provide robust evidence that the extreme summer droughts across North China is accompanied with a positive EU pattern, which is favorable for anomalous northerly currents, weakening the EASM, thereby inducing extreme droughts over North China
Summary
Since the ocean-atmosphere coupled general circulation models (CGCMs) that make use of oceanic memory (e.g., El Niño SST anomaly) for seasonal forecasting have been widely used to provide drought early warning[23,24,25], it is essential to understand whether a strong El Niño indicates a higher predictability of extreme summer drought in North China. The reduction in high-latitudes snow cover plays a crucial role in triggering such circulation pattern Along this line, a dynamical-statistical forecasting approach that merges preceding Eurasian spring snow cover and the CFSv2 predicted El Niño is established, and the approach shows more reliable predictions for extreme droughts in North China at long forecast lead
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