1920～2000年全球6～8月陆地旱涝气候变化

CLIMATIC CHANGE OF GLOBAL LAND FLOOD/DROUGHT IN JUNE——AUGUST DURING 1920——2000

用 192 0～ 2 0 0 0年全球 6～ 8月陆地降水量资料研究了全球、北、南半球 6～ 8月旱涝特征。采用加权平均的 6～ 8月降水距平指数和加权平均的 6～ 8月旱涝面积指数来表示全球的旱涝程度 ;从而划分了 192 0～ 2 0 0 0年的全球 6～ 8月降水量的旱涝年。对划分的旱、涝年进行了旱涝年差异的MonteCarlo检验。研究结果指出 ,在 192 0～2 0 0 0年中 ,1988( 193 0 )年是全球最严重的涝 (旱 )年 ,其次是 195 4( 1976)年。全球的及北、南半球的旱涝有明显的年代际变化。 2 0世纪 2 0年代为全球 6～ 8月干旱多发期 ,2 0～ 40年代为全球 6～ 8月洪涝少发期 ,5 0～ 60年代为全球洪涝多发期 ,70年代～ 2 0 0 0年全球旱涝爆发频繁 ,旱年多于涝年。北半球的特征与全球较为一致。南、北半球陆地分别作用为一个整体 ,它们的 6～ 8月旱涝没有明显的联系 ,但是当发生暖 (冷 )事件时 ,南、北半球 6～ 8月可能出现干旱 (洪涝 ) ,全球 6～

The flood/drought characteristics of global, northern and southern hemisphere in June-August are investigated by using global land precipitation dataset during the period of 1920-2000. The following two weighted mean indices are used to describe the extent of global flood/drought. (1) The weighted mean June-August precipitation anomaly index: the June-August precipitation anomaly (the 1920-2000 mean was used) at each grid point was multiplied with the cosine of the latitude of the grid point, and added together to get a series of 81 years. Normalizing the series yielded the global weighted mean June-August precipitation anomaly index. The larger the index, the more the mean precipitation, thus directly reflecting the interannual change of global June-August total rainfall. (2) The weighted mean June-August flood/drought area index:adding all the cosine of the latitude of the grid points of June-August positive precipitation anomalies yielded a series of 81 years, and normalizing the series got the weighted mean June-August flood/drought area index. The larger the index, the larger the wet area, thus directly reflecting the global June-August mean flood/drought area. There is a higher positive correlation (correlation coefficient=0.71) between the two global dry/wet indices. The two series indices from 1920-2000(81 years) were sorted descendently according to their values respectively,and then the first 20 years and the last 20 years in the two sorted seried were defined as global flood and drought years respectively. The differences between flood and drought years are examined with Monte Carlo test. The results indicate that 1988 (1930) is globally the wettest (driest) year during the period, and the next is 1954 (1976). The flood/drought characteristics experienced decadal change: during 1920s global drought in June-August occurred frequently, and from 1920s to 1940s global flood year in June-August occurred infrequently, then flood years were globally observed in the period of 1950s-1960s.In the period from 1970s to 2000 global land flood/drought frequently happened with flood years more than drought ones. The flood/drought characteristics of Northern Hemisphere are agreed with ones of the global. The southern and northern hemisphere are taken as a whole respectively, and no obvious correlation is found between the northern and southern hemispheric June-August flood/drought. However when the warm (cold) event occurs, the drought (flood) may happen in June-August in the southern and northern hemispheres. The global land flood/drought in June-August are highly correlated with the ENSO events.