Lake levels in Asia at the Last Glacial Maximum as indicators of hydrologic sensitivity to greenhouse gas concentrations

Using monsoonal and arid Central Asia as a case study, we have compiled lake level information from proxy records for the Last Glacial Maximum (LGM) and compared these to the simulated hydrologic cycle from four 21 ka model experiments completed for the Paleoclimate Modeling Intercomparison Project, phase 2 (PMIP2). Our new review of proxy records indicates that lake levels were nearly all lower at LGM compared to the pre-industrial across Asia. This water-balance pattern is largely reproduced by all four models and results from decreased precipitation during the LGM. An offline lake energy balance model forced with output from the PMIP2 models shows that lake evaporation also significantly decreased at LGM, but that in most areas the change in lake evaporation is overshadowed by changes in precipitation. Based on the model experiments, higher LGM lake levels only existed in the dryland regions of Pakistan, Afghanistan and north of monsoonal East Asia (similar to 45 degrees N, similar to 90-120 degrees E), which differs from previous studies that suggested that higher lake levels prevailed during the LGM in western China and arid Central Asia. A detailed atmospheric water budget analysis performed with output from the Community Climate System Model version 3 (CCSM3) indicates that a combination of atmospheric dynamics (i.e., convergence) and thermodynamics (i.e., the Clausius-Clayperon relationship) were responsible for decreases in LGM precipitation in Siberia and monsoonal Asia. Our results support the idea that monsoonal Asia will become wetter in the future due to increased atmospheric greenhouse gas concentrations, though more than atmospheric thermodynamics may be at play. The situation is more complex for arid Central Asia, though current trends towards wetter conditions there might be consistent with the pattern we observe and model for LGM. (C) 2012 Elsevier Ltd. All rights reserved.