SURFACE OBSERVED GLOBAL LAND PRECIPITATION VARIATIONS DURING 1900-88

The authors have analyzed global station data and created a gridded da taset of monthly precipitation for the period of 1900-88. Statistical analyses suggest that discontinuities associated with instrumental err ors are large for many high-latitude station records, although they ar e unlikely to be significant for the majority of the stations. The fir st leading EGF in global precipitation fields is an ENSO-related patte rn, concentrating mostly in the low latitudes. The second leading EOF depicts a linear increasing trend (similar to 2.4 mm decade(-1)) in gl obal precipitation fields during the period of 1900-88. Consistent wit h the zonal precipitation trends identified in previous analyses, the EOF trend is seen as a long-term increase mostly in North America, mid -to high-latitude Eurasia, Argentina, and Australia. The spatial patte rns of the trend EOF and the rate of increase are generally consistent with those of the precipitation changes in increasing CO2 GCM experim ents. The North Atlantic oscillation (NAO) accounts for similar to 10% of December-February precipitation variance over North Atlantic surro unding regions. The mode suggests that during high-NAG-index winters: precipitation is above normal in northern (> 50 degrees N) Europe, the eastern United States, northern Africa, and the Mediterranean, while below-normal precipitation occurs in southern Europe, eastern Canada, and western Greenland. Wet and dry months of one standard deviation oc cur at probabilities close to those of a normal distribution in midlat itudes. Ln the subtropics, the mean interval between two extreme event s is longer. The monthly wet and dry events seldom (probability < 5%) last longer than 2 months. ENSO is the single largest cause of global extreme precipitation events; Consistent with the upward trend in glob al precipitation, globally, the averaged mean interval between two dry months increased by similar to 28% from 1900-44 to 1945-88. The perce ntage of wet areas over the United States has more than doubled (from similar to 12% to > 24%) since the 1970s, while the percentage of dry areas has decreased by a similar amount since the 1940s. Severe drough ts and floods comparable to the 1988 drought and 1993 flood in the Mid west have occurred 2-9 times in each of several other regions of the w orld during this century.