Annual variability in leaf area index and isoprene and monoterpene emissions during drought years in Texas

A pathway through which drought may affect estimates of emissions of isoprene and other biogenic volatile organic compounds is through changes in leaf area index (LAI), a key input parameter for biogenic emissions models. Spatial and temporal variations of an LAI product derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the relative impact of LAI versus meteorological fields and soil moisture on emissions of isoprene and monoterpenes were examined using the Model of Emissions of Gases and Aerosols from Nature (MEGAN) for four climate regions in eastern Texas. The four regions had diverse land cover and climatology during 2006-2011, years with recurring extreme to exceptional drought. Maximum monthly interannual LAI variations exceeded 20% in the North and South Central regions, but were less than 20% in East Texas and Upper Coast. Estimates of isoprene and monoterpene emissions in the two central regions were lower by as much as −24% due to significant reductions of LAI during droughts in 2006 and 2011. Maximum interannual variability in estimated monthly isoprene emissions exceeded 30%. Reductions in LAI during drought may be accompanied by increases in temperature and surface insolation that exert competing effects on biogenic emissions estimates.