EAST ASIAN MONSOON VARIABILITY AND GROUNDWATER RECHARGE IN NORTHERN CHINA

The drylands of the Alashan Plateau (northern China) are near the current northernmost extent of the East Asian summer monsoon and are sensitive to changes in monsoon intensity. Based on chloride mass balance within the unsaturated zone, we show that variability in desert rainfall infiltration over the last 700 years is approximately synchronous with century-scale fluctuations in moisture conditions portrayed in the northern Tibetan Plateau ice cores (Guliya and Dunde) and in Juniper tree ring reconstructions, which have been attributed largely to monsoon variability. The effect of input uncertainties on the chloride model is quantified with deterministic and stochastic sensitivity analyses. The impact of Asian monsoon variability on recharge in China contrasts with the lack of widespread response of Southwestern US desert recharge to the El Niño Southern Oscillation (ENSO), possibly due to differences in the role of xeric vegetation. The results demonstrate the utility of unsaturated zone chloride as a palaeoclimate proxy under suitable conditions, and may aid in predictions of hydrological response to future climate change in this region.