Mechanisms and prediction of concurrent heatwaves and droughts in July–August over northeastern China

Concurrent heatwaves and droughts that occur over northeastern China (NEC) bring severe threats to human lives and crop productions. In the present study, a probability-based index that simultaneously considers precipitation deficiency and high temperature is calculated to represent concurrent heatwaves and droughts over NEC. Based on this index, the characteristics of concurrent heatwaves and droughts over NEC in summer are investigated using the year-to-year increment approach. The results indicate that the occurrence of concurrent heatwave and drought over NEC is closely related to the Polar-Eurasian teleconnection pattern and the Pacific-Japan teleconnection pattern. Further analyses indicate that the sea ice content in the Barents Sea in March (SICBS), the La Niña-like sea surface temperature (SST) in February (SST-PC1), and the northwestern Siberia soil moisture in April (SM) are coincidently linked to the two teleconnection patterns mentioned above. Based on their corresponding physical mechanisms, these three independent predictors are chosen to construct a physical-empirical prediction model for the prediction of concurrent heatwaves and droughts over NEC. Results suggest that this physical-empirical prediction model performs well with a high correlation coefficient and a low root mean squared error between the observed and predicted concurrent heatwaves and droughts over NEC for the period 1979–2018. Moreover, the cross-validation test and independent hindcasts both suggest that the physical-empirical model proposed in the present study with the three independent predictors has good prediction skills.