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.