关键词: 黄河流域, Z指数, 夏季旱涝, 周期变化

Abstract: Based on the NCAR/NCEP reanalysis data and precipitation data in 160 weather stations from the National Meteorological Center from 1951 to 2008, the distributions of summer precipitation in the Yellow River valley were analyzed. The interdecadal variations of the summer drought and flood were discussed. The results indicate that there are 9-11 years and 2-3 years cycles for the summer drought and flood in the Yellow River valley before 1990s, while those are not obvious after 1990s. The climatic physical factors leading to the summer drought and flood are analyzed in the Yellow River valley. It shows that the negative anomaly abnormality of geopotential height field over East-Asia results in summer drought directly, while the height anomaly field with the east high and west low over Asia leads to summer flood in the Yellow River valley. The convergence of South Asia monsoon and East Asia monsoon in summer is the key factor causing increasing precipitation in the Yellow River valley. For the OLR anomaly field in the same period, the area of the Yellow River valley shows the large negative anomaly in flood year, and the strong convection facilitates vapor convergence. Surface sea temperature (SST) field is the main influencing factor. SST index of equatorial eastern pacific has a negative correlation with summer precipitation in the Yellow River valley in the same period. Equatorial eastern pacific SST is often a positive phase in drought year, while it is often a negative phase in flood year. An analysis method of drought and flood is proposed, and it can provide scientific references for drought and flood prediction.