Evaporation from White Bear Lake and its Relation to Water Level


Ke Xiao (instead of Dr. John Baker)
PhD Candidate of Land and Atmospheric Science, Department of Soil, Water, and Climate

December 9, 2016


SESSION CHANGE - Ke Xiao instead of Dr. Baker

Ke will talk about how White Bear Lake (WBL) provides enormous economic and recreational benefits to citizens in the surrounding area. In the Twin Cities Metropolitan Area, many lakes have been at historic low levels and water augmentation strategies have been proposed to alleviate the problem. The water level of WBL declined 1.5 m during 2003–2013 for reasons that are not fully understood. Here, we report measured evaporation from WBL from 2014 to 2016 using two eddy covariance (EC) systems to provide better constraints on the lake water budget and to investigate the relation between evaporation and lake level changes. The annual evaporation from 2014 to 2016 was 534±80 mm, 636±60 mm, and 624±40 mm, respectively. Wavelet analyses reveal that net radiation and water heat storage control the seasonal variability in evaporation, while turbulence and vapor pressure gradient near the lake surface trigger large evaporation events at the daily scale. The EC measurements were used to tune the Community Land Model 4 – Lake, Ice, Snow and Sediment Simulator (CLM4-LISSS) to estimate lake evaporation over the period 1979-2016. The retrospective analysis of WBL evaporation indicates that evaporation increased by 3.9 mm per year, but there are no significant trends identified in the exchange between lake water and groundwater flow. Using a “business-as-usual” greenhouse gas emission scenario (RCP8.5), we modeled lake evaporation forward in time from 2016 to 2100. Model results suggest that annual evaporation will increase 1.3 mm/yr (3.3 million gal/yr) over this century, which is largely driven by the extended ice-free periods. These results have important implications for water management and water augmentation scenarios that are currently being proposed for WBL.