Landscape Response to Climate and Human Impact in Western China During the Han Dynasty

Abstract

The Chinese empire experienced a large expansion to the arid regions in the west during the Han Dynasty (206 BCE–220 CE). The Hexi Corridor, the Yanqi Basin, the southeastern part of the Junggar Basin and the Tarim Basin became part of the empire. The expansion of the Han Dynasty was accompanied by the significant intensification of irrigation farming along rivers draining the Qilian, Tianshan and Kunlun Mountains. Sedimentological and geochemical analyses and dating of lake sediments and shorelines revealed that four large lakes in the region experienced falling levels, or were almost or completely desiccating. The level of Zhuyeze Lake was falling rapidly ca. 2100 years before present (a BP), and the accumulation of lake sediments was replaced by an alluvial fan setting in large parts of the basin. Lake Eastern Juyan desiccated ca. 1700 a BP. Lake Bosten experienced low levels and increasing salinities at ca. 2200 a BP. Lake sediments in the Lop Nur region were mostly replaced by aeolian sands during a period of near-desiccation at 1800 a BP. In contrast, records from fifteen lakes farther in the west, north or south of the Han Dynasty realm indicate relatively wet climate conditions ca. 2000 years ago. Thus, dramatic landscape changes including the near and complete desiccation of large lakes in the arid western part of today’s China probably resulted from the withdrawal of water from tributaries during the Han Dynasty. These changes likely represent the earliest man-made environmental disasters comparable to the recent Aral-Sea crisis.