Effects of AO and Pacific SSTA on severe droughts in Luanhe River basin, China

Abstract

The frequency of drought occurring in the Luanhe River basin in China has increased since 1965. The severe droughts are mainly influenced by the negative phase of Arctic Oscillation (AO) and the 12-month time-lag La Nina events. In this study, we investigate the mechanism of the severe droughts occurring in the Luanhe River basin due to the 12-month time-lag Pacific sea-surface temperature anomaly (SSTA) and AO in the Luanhe River basin for the period of 1965–2012. According to the 3-month time scale of the low-level circulations and SSTA in the Pacific Ocean, when AO is in a continuous negative phase, the geopotential height at the 500-hPa level over high-latitude regions, such as Siberia, Lake Baikal and the Ural Mountains, decreases. The Europe–Asia wave train is located southward, which results in meridional anomalous circulation prevailing over East Asia. Due to air–sea interactions, the 12-month time-lag Pacific SSTA weakens the northwestern Pacific subtropical high and blocks the warm air from the Pacific. When the negative phase of AO and La Nina happened simultaneously during 1971/1972, the first stage of 2000/2002 and 2008/2009, a severe drought occurred in the Luanhe River basin. A severe drought happened in this region during 1980/1981 and the third stage of 2000/2002 when AO was in the negative phase.