Influence of seasonality, canopy light extinction, and terrain on potential isoprenoid emission from a Mediterranean-type ecosystem in France

Abstract

Sensitivity studies for simulations of yearly cycles and terrain effects are presented for the St.-Martin-de-Londres region (southern France). Potential isoprenoid emissions are simulated using the Solar Radiation Model (SORAM), spatial effects of complex terrain, photosynthetically active radiation, and surface temperature. SORAM is embedded in a geographic information system (GIS) environment and considers a digital elevation model (DEM) of the model domain. Compared to the maximum case (i.e., no variation in emission factors and leaf area index (LAI)), seasonality in LAI for that Mediterranean-type landscape mainly covered by evergreen plant species resulted in an annual amount of 3.5% less for total isoprenoids. By including the intra-annual change in emission factors an additional 12.5% reduction was derived for the area. When the SORAM module that accounts for light extinction within the canopy was switched off, modeled yearly amount in emission increased by 48%. Complex terrain effects showed only a weak influence for the rather moderate terrain of the modeling domain (mean difference of approximately -2.5% in daily sums). However, sensitivity studies based on the DEM exaggerated by a factor of 2 (resulting in differences of -11.7% for the light-and temperature-dependent isoprenoids) revealed that in the case of pronounced relief or if highly resolved results are necessary, the orography should be considered when modeling the driving parameters of light and temperature.