March 2012 was a month for the climatological record books, with anomalously warm temperatures prevalent across much of the Contiguous United States. Numerous stations recorded their all-time warmest March mean temperature, including the greatest departure above normal for any month.
These unusually warm temperatures translated into an early, rapid green-up in the deciduous vegetation across much of the eastern half of the United States. This rapid green-up is captured well by the real-time SPoRT/MODIS vegetation product, which is produced once per day at 0.01° resolution over the U.S. lower 48 states and adjacent portions of southern Canada and northern Mexico. The figure below shows a one-year change in the SPoRT/MODIS Greenness Vegetation Fraction (GVF) product from 2011 to 2012, valid on 11 April. Most of the eastern U.S. has larger GVF than last year by 10% or more. In fact, a significant part of southeastern Canada has GVF increases over 40% compared to last year. Parts of the Tennessee / Mississippi river valleys, and New England also have year-to-year increases of comparable magnitude.
Such dramatic inter-annual changes in the health and coverage of green vegetation can have significant impacts on the surface energy budget within numerical weather prediction models. The default vegetation dataset in community models such as the WRF model consists of a climatology that depicts vegetation coverage the same from year to year. In anomalous situations such as this Spring, the climatological dataset would likely mis-represent the coverage of vegetation in the model, thus negatively affecting the energy exchanges between the land surface and planetary boundary layer. Therefore, the use of real-time vegetation, such as the SPoRT/MODIS product, has the potential to better represent vegetation coverage and the subsequent surface energy budget in real-time models.