579 Stem-root flow effect on land-atmosphere interaction

Wednesday, 13 January 2016
New Orleans Ernest N. Morial Convention Center
Tzu-Hsien Kuo, National Taiwan University, Taipei, Taiwan; and J. P. Chen

Via the stem-root flow mechanism, water in surface soil can rapidly enter the deeper layers, causing redistribution of soil water in the vertical. In this study, the stem-root-flow mechanism is formulated and implemented into the Community Land Model (CLM) v4.0 that coupled with the Community Earth System Model (CESM) v1.0.3 The models were run in both offline mode and atmosphere-land interactive mode, to investigate its long-term hydrological impacts. Results from the offline mode showed that stem-root flow generally causes a decrease in the moisture content at the top soil layer while moistens the deeper soil layers. Such soil moisture redistribution leads to considerable changes in heat flux exchange between land and the atmosphere.

The atmosphere-land coupled simulations showed that greatest changes in surface temperature and radiation fluxes occurred over the U.S. Great Plains, some regions of India, Ukraine, and southern Yemen, as a result of the stem-root flow. However, the responses may be different than that found in the offline mode in some of the places. For instance, Ukraine and southern Yemen region experienced increasing soil moisture in the top layer. These nonlinear responses are mainly due to dynamic feedbacks which altered the atmospheric circulation, precipitation, and evapotranspiration. Therefore, soil-precipitation feedback mechanism includes local and regional effects. Also, changes in heat flux can alert convection and thus precipitation, which in return controlling the capacity of evapotranspiration. For example, the increase in summer time precipitation over the Ukraine region is largely due to the higher moist static energy with higher latent heat flux associated with increased top-soil moisture; whereas in Yemen, the changes in horizontal temperature gradient can trigger the convergence and, as a result, an enhancement in precipitation. Further investigation is needed to fully understand the causality of soil-precipitation relationship associated with the stem-root flow mechanism.

- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner