Image courtesy NASA Goddard Space Flight Center Biospheric Sciences
Branch, based on data from NOAA.
This image shows the difference between the amount of vegetation in July
2000 and the average July vegetation for North America. Of particular
interest are the dry conditions in the western United States. This spring and summer
the Rocky Mountains have been relatively dry, and the brown regions
stretching from the Canadian to the Mexican border, indicate the effect
on the regions' forests. Western Montana and eastern Idaho are
particularly parched, and appear darker brown. The dry conditions
have contributed to this year's devastating fire season, during which
millions of acres have burned in the west.
Scientists find that during the growing season, land plants can be used
to measure drought. Healthy, thriving plants reflect and absorb visible
and near-infrared light differently than plants under stress. These
variations in reflectance and absorption can be measured by satellites
to produce maps of healthy and stressed vegetation. This image shows
Normalized Difference Vegetation Index (NDVI) anomaly, which indicates
where vegetation growth was above average (green pixels), below average
(brown pixels), or normal (white pixels).
This image originally appeared on the Earth Observatory. Click here to view the full, original record.