Figure 6. 13-year summertime (MJJA) mean wetland storage level (a); and difference between wetland storage (WS) and default (DEF) simulations in surface runoff (b), evapotranspiration (ET, c), sensible heat flux (d), and latent heat flux (e).
3.3 Regional climate simulation with coupled wetland dynamics
To study the feedback from wetlands to regional climate, we performed two coupled WRF-wetland simulations for the summers of 2005, 2006, and 2007. The first, default (DEF) simulation includes the shallow groundwater scheme from Miguez-Macho et al. (2007). The second simulation (WS simulation) incorporates the wetland scheme upon the shallow groundwater scheme. These simulations start from April and run through August, with the first month as the spin-up period. Our analysis focuses on the temperature and precipitation from May to August for these three years, especially in 2006 when an intense summer heatwave occurred from mid-July to early August in the Central U.S. and Southern Canada.
Figure 7 shows the monthly temperature from station observation, model biases from two simulations, and the cooling effect induced by the WS scheme in 2006. It is clear that a warm bias exists in the southern part of the domain, ranging from 2 in the Central U.S. to 1 in the Western Canadian Prairies. This warm bias is particularly getting stronger in July and August. The WS simulation shows a significant cooling effect in the Northeast portion of the domain, where the saturated fraction is high. The cooling in temperature ranges from less than 1 in May to about 1~2 in July. This cooling signal is evident in high-Fsat regions in the domain in all three-year simulations.