Changes in dryness/wetness in China during the last 529 years

Historical written records of weather conditions that affect agriculture an d living conditions in China can serve as a proxy for instrumental observat ions of the relative wetness and dryness, or precipitation amounts, for per iods of time dating back to at least AD 1470. The dryness/wetness index (DW ) data at 100 selected sites and at a subset of 25 sites with entirely cont inuous data indicate that during the growing season the number of sites wit h dryness increased rapidly in the 20th century, in contrast to a gradual i ncrease and levelling off of wetness since the 18th century. Dry conditions existed mostly in northeastern China in the 16th and 17th centuries. In th e 20th century, dryness prevailed in most areas in China, and the chance of occurrence at each site increased. Wet conditions have expanded from east coastal areas to inland since the 19th century. As a result of increased dr yness and wetness, the number of sites experiencing normal precipitation co nditions has dropped dramatically. The number of sites with extreme dryness /wetness has also increased during the 20th century, and the spatial distri bution of the sites with a large chance of extreme dryness/wetness has also changed. The frequent occurrences in dryness/wetness as well as in extreme s in the 20th century seem indicative of an abnormality in climate on a lar ge scale. Spectral analyses of the DW data has revealed that cycles in dryn ess/wetness and their extremes have existed with periods on relatively shor t time scales as well as on the long time scales. The possible existence of a century-scale cycle suggests that caution should be used in relating var iations in rainfall conditions to global warming. Copyright (C) 2000 Royal Meteorological Society.