What a difference a year makes!

The Southern Plains of the U.S. is in the grips of a serious heat wave and drought this summer.  Temperatures have been soaring into the 100s and even 110s routinely over Texas and Oklahoma in recent weeks, with little to no widespread rainfall.  Recall, however, that last summer’s conditions were quite different with substantial rain and moist conditions from Mexico up to Colorado.

SPoRT has been generating a daily-updated Greenness Vegetation Fraction (GVF) over the Continental U.S., which is derived from MODIS overpasses of Normalized Difference Vegetation Index that measure the coverage of healthy green vegetation from the near-IR and red-visible channels.   Figure 1 shows the SPoRT GVF from last summer, valid 1 August 2010, centered on Texas.  This image show fairly large values of GVF for the region, especially over west Texas and Mexico.  Meanwhile, the SPoRT GVF for 1 Aug 2011 (Fig. 2)  depicts markedly different values of vegetation.  GVF values are considerably lower over much of Mexico, Texas and Oklahoma.  The difference field in Fig. 3 highlights the area of decreased GVF over the region.  Some local areas have seen decreases in GVF of over 40%.

Such dramatic variations in GVF from one year to the next can have significant ramifications  to numerical weather prediction, because operational models typically employ a climatological GVF that remains the same year-to-year.

Figure 1. SPoRT/MODIS daily 1-km GVF valid 1 Aug 2010.

Figure 2. SPoRT/MODIS daily 1-km GVF valid 1 Aug 2011.

Figure 3. Difference in SPoRT/MODIS GVF (1 Aug 2011 - 1 Aug 2010).

2 thoughts on “What a difference a year makes!

  1. Fantastic post! This has created lots of discussion here at WFO ABQ. We have noted lots of days with southeast flow into New Mexico which is usually very good for our monsoon, especially within the Rio Grande Valley. Storms that form over the central mountains east of Albuquerque move off the high terrain and essentially disappear as the move into the Rio Grande Valley with little more than blowing dust and a 10 degree temperature drop. This year rainfall has been very spotty with many areas still receiving less than 1 inch of precipitation for the year. We have also noted that the medium to extended range models keep developing monsoonal moisture surges into the area that gradually diminish as they approach the short term and materialize in a spotty nature. Drought feeds drought?

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