A half-century drying in Gobi Oasis, possible role of ENSO and warming/moistening of Northwest China

To investigate the historical wet/dry fluctuations in Gobi Oasis and its driving mechanism under the background of global warming, a climatological study of tree-ring stable oxygen isotope (δ¹⁸O) was carried out in the Gobi Oasis in northwest China. Based on the tree-ring δ¹⁸O sequence of Populus euphratica, the 124-year (1886–2009) June–August relative humidity history of the oasis was reconstructed, explaining 49.2 % of the total variance of the meteorological observation during 1960–2009. The reconstructed sequence captured the changing characteristics of the relative humidity in the oasis in summer and showed that the wet years in the past 124 years mainly occurred before 1950s, while the relative humidity showed a continuous downward trend after 1950s. The spatial correlation shows that the reconstructed summer relative humidity has good spatial representation and can reflect the large-scale relative humidity variations in Northwestern China from June to August, and is consistent with other paleoclimate reconstructions in adjacent areas. The comparison found that the reconstructed sequence was significantly correlated with the dry-wet indices in the westerlies region at both high and low frequencies, and was significantly correlated with the reconstructions in the monsoon region at low frequency, which imply that the relative humidity in the oasis in summer might be affected by both the westerlies and the East Asian summer monsoon. In addition, we found that the changes in summer relative humidity in the oasis were related to large-scale air-sea interactions. The El Niño-Southern Oscillation (ENSO) in the central Pacific was the main influencing factor.