Trends in Satellite-Derived Vegetation Roughness Length for Momentum over the Conterminous U.S.

Contemporary land surface model (LSM) parameterizations require information about vegetation roughness for purposes of characterizing fluxes of momentum, heat, and other scalars between the surface and atmosphere. The simplest parameterizations rely on vegetation type and height alone, while more-realistic alternatives incorporate spatially variable canopy density and/or height information, which may be derived from field observations or satellite data. This research focuses on the latter – a time series of spatially-explicit roughness fields estimated from both passive and active remote sensing products. Our intent is to provide a climatic perspective on the spatiotemporal evolution of vegetation roughness length.

Here, the satellite-based roughness fields are derived from 8-day MODIS leaf-area index data at 500-meter spatial resolution, and canopy height information provided by the ATLAS/ICESat-2 Land and Vegetation Product at 20-m along track. We describe a) processes of computing indicators used to build the trends, and b) the resulting trend maps, which illustrate magnitude and direction of change in vegetation roughness over a 17-year period of record. In addition, we present a statistical analysis of the trends, to include effects of spatial aggregation as well as differences across vegetation types.