Tale of Two Marches: Effect on Vegetation

An interesting picture has been making the rounds though social media showing the temperature departure from average for the first 18 days of March 2012 compared to this March, courtesy of Climate Central via the NWS Twin Cities, MN (Fig. 1; original article posted at: http://www.climatecentral.org/news/from-heat-wave-to-snowstorms-March-weather-goes-to-extremes-15763). March 2013 is almost a mirror image of the temperature anomaly map from last March, although not to the same magnitude of departure.

Fig. 1.  Temperature anomalies for 1-18 March 2012 (left) compared to 1-18 March 2013 (right).

Figure. 1. Temperature anomalies for 1-18 March 2012 (left) compared to 1-18 March 2013 (right), courtesy of Climate Central.

The effect of these radically disparate temperatures are now being seen in the SPoRT real-time MODIS vegetation product, which is generated once daily at 0.01-degree resolution (~1 km) over the Continental U.S.  Figure 2 shows a comparison between the 22 March 2012 SPoRT-MODIS green vegetation fraction (GVF) composite and the MODIS GVF composite generated a year later.  Brown regions indicate the lowest fractional coverage of healthy green vegetation, while dark green colors show areas of dense, healthy vegetation.  The most noticeable differences in GVF can be seen over the Great Lakes, southern Canada and the southern Plains.  A difference field in Fig. 3 shows more clearly the magnitude of the one-year GVF change.  Portions of Canada, the Great Lakes region, northeastern U.S., and the Southern Plains are seeing lower GVF by about 20-50% compared to last year at this time.  These GVF comparison images are available daily on SPoRT’s web page at http://weather.msfc.nasa.gov/sport/case_studies/sportGvf.html, and could be further accentuated given the prospect of continued below-average temperatures through 1 April in the eastern U.S.

Because GVF can vary so widely in certain regions from year to year, it is important to use actual vegetation data rather than a multi-year climatological representation in numerical weather prediction (NWP) applications.  Such large GVF differences during the transition seasons can lead to errors in how the NWP model partitions incoming solar energy into heat and moisture fluxes at the surface.  SPoRT has made its real-time MODIS GVF product available to the modeling community using the Weather Research and Forecasting model and Environmental Modeling System.  Currently, two of SPoRT’s collaborating partners in the National Weather Service (Houston, TX and Mobile, AL forecast offices) are assessing the utility of using real-time MODIS vegetation data in place of the default climatology GVF (in addition to other SPoRT datasets) within the framework of the Environmental Modeling System.

Figure 2. Comparison between the 22 March SPoRT/MODIS green vegetation fraction (GVF) from 2012 (left) and 2013 (right).

Figure 2. Comparison between the 22 March SPoRT-MODIS green vegetation fraction (GVF) from 2012 (left) and 2013 (right).

Figure 3. Annual difference (2013 – 2012) in SPoRT-MODIS GVF valid on 22 March.

Figure 3. Annual difference (2013 – 2012) in SPoRT-MODIS GVF valid on 22 March.

2 thoughts on “Tale of Two Marches: Effect on Vegetation

  1. Great post Jon! Although, NWS Huntsville has also begun using the MODIS GVF product in our local modeling efforts. Given the coolness of the current March, it will be interesting to see if this has much predictive impacts in the model over the GVF climatology.

  2. Thanks Kris. Yes, there are several forecast offices beginning to incorporate the SPoRT-MODIS vegetation into their local model runs. Right now, there isn’t much of an annual difference over the southeastern U.S., but that may change in the near future as we continue to delay this Spring’s green-up. The vegetation response typically lags the temperature/precipitation anomalies by a few weeks.

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