The developments in ORCHIDEE land surface model and the interaction with atmosphere
Dr. Fuxing Wang
This report focuses on the role of soil thermodynamics and groundwater table in land-atmosphere interaction using the ORCHIDEE LSM coupled with LMDZ atmospheric model. The report includes three parts. First, the soil thermodynamics of ORCHIDEE LSM has been improved by implementing a new vertical discretization, by parameterizing the thermal properties as a function of soil moisture and texture, and by modelling heat transported by liquid water into the soil. The changes of soil thermal properties (conductivity and capacity) lead to significant changes in the surface energy budget, with the strongest effects taking place over dry areas and during the night. Second, the impacts of water table depth on the near surface climate were studied using the LMDZ-ORCHIDEE model. Saturating the bottom half of the soil induces an increase of evapo transpiration over water-limited regimes due to increased soil moisture, but it decreases over energy-limited regimes due to the decrease in downwelling radiation and the increase in cloud cover. Over the West African Monsoon and Australian Monsoon regions, the precipitation changes in both intensity (increases) and location (poleward). The tropical and mid-latitude areas show a decrease in air temperature (−0.5 K over mid-latitudes and −1 K over tropics) and an increase in precipitation. Third, the fresh water input into the Mediterranean sea was estimated by assimilating river discharge in the ORCHIDEE LSM. The new estimation is about 200 km3/y higher than the values reported in the literatures (e.g., 300-400 km3/y).