Persistent dry weather has grown more worrisome in the Western United States, with nearly two-thirds of the region experiencing drought. By most measures, California is suffering the worst of it.
The accompanying map shows the impact of drought on California’s farms, forests and wild lands. Based on data from NASA’s Terra and Aqua satellites, the map contrasts plant health from Jan. 17 to Feb. 1, 2014, against average conditions for the same period during the last decade.
Shades of brown depict where plant growth, or “greenness,” was below normal for the time of year; shades of green indicate vegetation that is more widespread or abundant than normal. Grays depict areas where data weren’t available (often due to cloud cover). The map is based on the Normalized Difference Vegetation Index, a measure of how plant leaves absorb visible light and reflect infrared light. Drought-stressed vegetation reflects more visible light and less infrared than healthy vegetation.
There’s some surprising greenness along the edges of the Sierra Nevada range. “In a normal year, much of the green areas near the mountains would be snow-covered,” says Ramakrishna Nemani, a vegetation sensing expert at NASA’s Ames Research Center. “Because there isn’t much snow this year, the evergreen vegetation appears anomalously green. In fact, that is bad news for this time of the year.”
Image courtesy of NASA.