Abstract ID: 124

Atmospheric and Hydrological Controls of the Evapotranspiration Over a Floodplain Forest in the Bananal Island Region, Amazonia.

This paper discusses seasonal and interannual variations of the evapotranspiration (ET) rates in Bananal island floodplain, Brazil. Measurements included evapotranspiration and sensible heat flux using the eddy covariance method, atmospheric forcings (net radiation, Rn, vapor pressure deficit, VPD, wind speed and air temperature), soil moisture profiles, groundwater level and flood height, taken from November 2003 to December 2006. Seasonal analyses had shown that evapotranspiration decreased in the dry season (average 3.6 mm.day-1), despite the simultaneous increase in Rn, air temperature and VPD. The increase of ET in the wet season and particularly in the flood period (average 4.2 mm.day-1) showed that the free water surface evaporation strongly influenced the energy exchange. For the hydrological year (Oct-Sep) of 2003/2004, 2004/2005 and 2005/2006, the accumulated precipitation was 1692, 1471, 1914 mm and the accumulated ET was 1361, 1283 and 1317mm, respectively. 2005 was considered an anomalously dry year for the region, which caused the lowest ET values within the observation period. Soil moisture, which was substantially depleted during the dry season, and adaptative mechanisms such as leaf scenecense of the vegetation contributed to limit the dry season ET. Strong drainage within permeable sandy soils helped to explain the soil moisture depletion. These results suggest that the Bananal flooding area shows different patterns in relation to the upland Amazon forests: i) seasonal ET variation is not in phase with Rn; ii) the wet season ET is higher than the dry season ET, and iii) the system is sensitive to extended drought periods.

Session:  Carbon - The role of seasonality in carbon and water balance.

Presentation Type:  Oral