Impact of Seasonal Changes in Leaf Area on Evapotranspiration of a Teak Plantation in a Dry Tropical Area
Abstract
In the study, a soil-plant-air (SPAC) continuum multilayer model was used to numerically simulate evapotranspiration (ET) and soil moisture in 2001-2006 in a deciduous teak plantation in a dry tropical climate of northern Thailand, to examine the influence of seasonal changes in leaf area index (LAI) and the inter-annual variations in canopy duration period (CDP) from leaf appearance to complete leaf fall on ET. Two numerical experiments with different seasonal patterns of LAI were carried out using above-canopy hydro-meteorological data as input data. The first experiment involved seasonally varying LAI estimated based on time-series of radiative transmittance through the canopy, and the second experiment applied an annually constant LAI. The first simulation captured the measured seasonal changes in soil surface moisture; the simulated transpiration agreed with seasonal changes in heat pulse velocity, corresponding to the water use of individual trees. In the second numerical simulations, the constant LAI increased transpiration at small LAI, particularly immediately after leaf flush and toward the dry season. But, the seasonal changes in simulated transpiration were apparently similar to those in observed heat pulse velocity and they ceased during dry seasons. This implies that soil water, which is balanced in SPAC systems by precipitation, canopy interception, soil evaporation, soil water uptake by transpiration, and discharge, can mainly control the seasonal changes in transpiration and that it is also generally likely to influence CDP or forest growing season length (GSL), during which trees assimilate carbon. The constant LAI reduced downward radiation and wind velocity on the forest floor year-round and decreased soil evaporation during dry seasons. Further, soil evaporation did not quickly respond to rainfall events, but continued longer relative to that simulated at small plant area index (PAI).
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.B43A0414T
- Keywords:
-
- 1818 Evapotranspiration;
- 1840 Hydrometeorology;
- 1847 Modeling;
- 1866 Soil moisture;
- 1876 Water budgets