Water Resource Management Implications for a Desert Oasis From Tree-Ring δ¹⁸O Variations in Populus Euphratica in Northwest China

Paleoclimatic data has often been applied to demonstrate the influence of anthropogenic activities on runoff to desert rivers, and such features as reservoirs are clearly known to influence available water in downstream riparian settings. The impact of human activities on the hydrology of a downstream desert oasis is, however, an open question. High-resolution hydroclimate paleo-reconstructions for desert oases are lacking, partly because paleoclimate proxies in extremely dry deserts are insensitive to extremely low precipitation. Here, we first attempt to reconstruct regional precipitation (r = −0.743, p < 0.001, n = 49) for the interval 1886–2009 from the stable oxygen isotope ratio (δ¹⁸O) of five Populus euphratica trees growing in the Ejina Oasis, on the lower reaches of the Heihe River in extremely arid Northwest China. The δ¹⁸O series for P. euphratica in the oasis (∼900 m a.s.l) abruptly increases relative to an δ¹⁸O series of Qinghai spruce (Picea crassifolia) growing in upper limit of forest (∼3,000 m a.s.l) in Longshou Mountain (middle reaches of the Heihe River) after about 2000, when the Ecological Water Diversion Project on the Heihe River was implemented. This finding implies that the Ejina Oasis suffered from serious drought during the last decade, or at least that the Oasis is stressed more than expected by current climate conditions. Other evidence also indicates that human activities contributed to a decrease in air moisture in the Ejina Oasis after 2000. To mitigate water stress on the oasis, we recommend some practical measures to ensure the rational development of the desert oasis.