Abstract
Abstract. The Qaidam Basin in the north of the Tibetan Plateau has undergone drastic environmental changes during the last millions of years. During the Pliocene, the Qaidam Basin contained a freshwater mega-lake system although the surrounding regions showed increasingly arid climates. With the onset of the Pleistocene glaciations, lakes began to shrink and finally disappeared almost completely. Today, hyperarid climate conditions prevail in the low-altitude parts of the Qaidam Basin. The question of how the mega-lake system was able to withstand the regional trend of aridification for millions of years has remained enigmatic so far. This study reveals that the mean annual water balance, i.e. the mean annual change in terrestrial water storage in the Qaidam Basin, is nearly zero under present climate conditions due to positive values of net precipitation in the high mountain ranges and shows positive annual values during warmer, less dry years. This finding provides a physically based explanation for how mid-Pliocene climates could have sustained the mega-lake system and that near-future climates not much different from present conditions could cause water storage in reservoirs, raising lake levels and expanding lake areas, and may even result in restoration of the mega-lake system over geological timescales. The study reveals that a region discussed as being an analogue to Mars due to its hyperarid environments is at a threshold under present climate conditions and may switch from negative values of long-term mean annual water balance that have prevailed during the last 2.6 million years to positive ones in the near future.
Highlights
Paleogeographic studies (Chen and Bowler, 1986; Huang et al, 1993; Mischke et al, 2010; Wang et al, 2012; Fang et al, 2016) on the intermontane endorheic Qaidam Basin (QB), located in China’s desert region in the north of the Tibetan Plateau (TP), revealed that it once contained a mega-lake system during the mid-Pliocene and before
If Surface Energy Balance System (SEBS) values for annual actual evapotranspiration would be considered to be more accurate than the High Asia Refined analysis (HAR) 10 km data, annual water balance would have been positive throughout all years
This study was able to show that the mean annual water balance of the QB was close to zero during the 14 hydrological years from 2001 to 2014
Summary
Paleogeographic studies (Chen and Bowler, 1986; Huang et al, 1993; Mischke et al, 2010; Wang et al, 2012; Fang et al, 2016) on the intermontane endorheic Qaidam Basin (QB), located in China’s desert region in the north of the Tibetan Plateau (TP), revealed that it once contained a mega-lake system during the mid-Pliocene (ca. 3.3–3.0 Ma BP) and before. Paleogeographic studies (Chen and Bowler, 1986; Huang et al, 1993; Mischke et al, 2010; Wang et al, 2012; Fang et al, 2016) on the intermontane endorheic Qaidam Basin (QB), located in China’s desert region in the north of the Tibetan Plateau (TP), revealed that it once contained a mega-lake system during the mid-Pliocene Spatial details of the mega-lake system are not known, Chen and Bowler (1986) reported that the total lake surface was about 59 000 km during the early Pleistocene. Only a few saline lakes and playas exist, and the lowaltitude parts of the QB are hyperarid deserts (Chen and Bowler, 1986; Huang et al, 1993; Wang et al, 2012). The existence of a mega-lake system during this period implies that longterm mean annual water balance S, i.e. the total annual change in terrestrial water storage within the basin’s reservoirs (aquifers, soils, lakes, rivers, permafrost, snow covers, glaciers, etc.), was close to zero and did not show, on average, negative values over time periods of thousands of years or longer, because otherwise the mega-lake system would have temporarily dried out and produced layers of evaporites
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