Interannual variability in the surface energy budget over a large southern inland water: an analysis of two-year eddy covariance data

Understanding how the surface energy budget and evaporation over inland waters respond to climate variability is important in fresh water management. Here we report long-term measurements of the surface energy budget using the eddy covariance method over a large inland southern water body of the Ross Barnett Reservoir, Mississippi, U.S.A. for 2008 and 2009. The two-year averaged incoming solar radiation (K↓), net radiation (Rn), sensible heat flux (H), latent heat flux (LE), and energy balance residual (ɛ) were 178.5, 110.6, 15.7, 83.7, and 11.3 W m-2, respectively. The annual cycle of Rn was followed by LE, with maximums occurring in the summer and minimums in the winter. H was small in the summer and large in the winter. The Bowen ratio shows that a relatively large portion of Rn was used to fuel evaporation in the warm season (from April to September) and to power H in the cool season (from October to March). The annual mean H and LE were 9.5% and 10.0% larger in 2008 than 2009, respectively. Most of the interannual variations primarily occurred in the cool season, which was partly due to the H and LE pulses that associated with large wind events caused by synoptic weather activities (e.g., cold front passages). These pulses approximately contributed to 50% of the annual H and 28% of the annual LE. Their interannual variations contributed to 77.8% of the interannual variations in H and 39.8% of those in LE. Compared with higher-latitude large lakes, this southern mid-latitude water body experienced larger evaporative water loss but smaller sensible heat loss into the atmosphere.