Evolution and features of global land June–August dry/wet periods during 1920–2000

Dry/wet features for the globe and the Northern and Southern Hemispheres are investigated in terms of 1920–2000 June–August (JJA) global land precipitation data. The weighted mean JJA precipitation anomaly index and the weighted mean JJA dry/wet area index are used to describe the extent of global dryness/wetness. It is pointed out that 1988 (1930) was the globally wettest (driest) year in 1920–2000, and 1954 (1976) was the second wettest (driest). The dryness/wetness of the globe and Northern and Southern Hemispheres has shown distinctive interdecadal changes: during the 1920s, global dryness occurred in JJA frequently; from the 1920s to the 1940s global wetness occurred infrequently in JJA; the 1950s–1960s was a period of frequent global JJA wetness; and the 1970s to 2000 was a period of frequent global JJA dryness/wetness, with the number of dry years greater than that of wet years. The dry/wet features of the Northern Hemisphere are comparatively consistent with those of the globe, but there is no obvious relation between JJA mean precipitation anomalies of the two hemispheres. The analyses of the simultaneous and last winter sea‐surface temperature anomalies of global dry/wet years reveal that there is clear correlation of JJA global dry/wet change with sea‐surface temperature variations and El Niño–southern oscillation (ENSO) events. Global JJA dryness occurs when the summer ENSO (El Niño) is weaker, and global JJA wetness occurs when the summer ENSO is strong. The largest difference between the last winter sea‐surface temperature fields for global dry and wet years is that the sea‐surface temperature in the North Pacific and North Atlantic for wet years is substantially higher than that for dry years. Copyright © 2004 Royal Meteorological Society