| In order to reveal temporal and spatial characteristics of soil drought, the paper mainly uses the EOF, REOF and CEOF and wavelet analysis to study the 40-year (19612000) change of soil drought in the loess plateau. It finds that soil drought changed consistently across the region, tending to worsen, especially obvious in 1990's; it fluctuated with a two periods of which one lasted 24 years and the other lasted 79 years; it mostly varied with the period of 24 years; the worst soil drought often occurred between July and October during which soil drought spread from the middle of the plateau toward west, east and north; there were three sensitive regions to soil drought between July and October and they could be divide into three sub-regions whose drought intensities and frequencies much differed. |