Quantifying Evaporation and Its Decadal Change for Lake Nam Co, Central Tibetan Plateau

Abstract:

Most lakes in the interior Tibetan Plateau expanded rapidly since the late 1990s. Because of the lack of observations, the lake water balance and its change are far from well understood. Evaporation is a component of lake water balance, and this study quantifies its magnitude, decadal change, and its contribution to water balance change of Lake Nam Co, one of the largest lakes (with an area of about 2000 km² and a mean depth of about 40 m) in the Tibetan Plateau. The lake temperature and evaporation are simulated by Flake model. The simulated lake temperature during 2000 to 2012 is validated against MODIS observations and its mean bias error (model simulation minus satellite retrieval) and root mean square error are -0.44 ºC and 3.37 ºC during the day, and 0.02 ºC and 2.27 ºC at night, respectively. The simulated latent heat flux and sensible heat flux are in good agreement with Bowen-ratio-derived ones in 2012, indicating that the simulation results are reasonable. The simulated long-term mean annual evaporation is about 750-850 mm, and this value is much less than potential evaporation estimated with Penman-Monteith equation. The simulated annual evaporation over 1980 ~ 2012 displays a complex decadal oscillation, mainly due to the change in energy-related terms (air temperature, solar radiation and atmospheric long-wave radiation). The mean lake evaporation since the late 1990s is slightly greater than before, and thus evaporation change played a role in suppressing the recent expansion of Nam Co.