Spatio-temporal variability of drought over northern China and its relationships with Indian-Pacific sea surface temperatures

摘要

Monthly precipitation data from 66 rain gauge stations in northern China are analyzed for the period 1976-2011. Variations in droughts and wet spells are described using the standardized precipitation index (SPI). Empirical orthogonal functions and a global wavelet spectral analysis are applied to capture modes of spatio-temporal variability in droughts over northern China. Time series of monthly sea surface temperatures (SST) and the Multivariate El Nino Southern Oscillation Index (MEI) are presented, and cross wavelet and wavelet coherence transforms are carried out to investigate possible mechanisms behind variations in droughts and wet spells. From 1976 onwards, the northern parts of northern China have experienced an increase in the frequency of droughts, while the southern parts of northern China have experienced a decrease in the frequency of droughts. The north-south variability of droughts and wet spells is characterized by interannual timescales of 3.3 years and 7.0-11.0 years. The former timescale is closely related with the MEI, while the latter is closely related with sea surface temperature anomalies (SSTA) over the North Pacific. Most parts of northern China experienced an increase in the frequency of droughts during the periods 1980-2000 and 2004-present, and a decrease in the frequency of droughts during the period 2000-2004. The variability of drought in northern China peaks at timescales of 16.0-32.0 and 3.5-4.0 years. The first of these timescales shows a significant correlation with SSTA over the Indian Ocean. The eastern parts of northern China have experienced a decrease in the frequency of droughts since 1976, while the western parts of northern China have experienced an increase in the frequency of droughts. The east-west variability of droughts and wet spells is characterized by interannual timescales of 3.3-8.0 years, which are related with SSTA over the Indian Ocean warm pool.