Abstract: Drought disaster can lead to the dry up of reservoirs, river cutoff, decrease of underground water level and agricultural production, human and animal drinking water problems, etc. Huang-Huai-Hai River Basin, outstood by serious drought-flood problems, has the drought disaster area and frequency ranked the top in China. Now, with the rapid economic development, population expansion, and the climate change anomalies, natural ecological environment in Huang-Huai-Hai River Basin was badly worsened, and the drought and flood disasters occurred more frequently. Therefore, an efficient drought and flood monitoring and drought assessment method is very urgent. Based on daily weather and soil data of 145 weather stations in the Huang-Huai-Hai River Basin for nearly 53 years, and selecting modified Palmer Index, standardized precipitation index(SPI)and precipitation anomaly percentage(Pa)as evaluation indexes, this paper made an comparative analyses of the three indexes in evaluating the drought-flood period, mutation point and trend of drought and flood situation by using wavelet analysis, Mann-Kendall test and moving T test. Meteorological data was from the National Weather Service Data Center, and the main soil data adopted the ERA40 soil moisture data(medium-range forecasts from the European Centre)from 1961 to 2013. Results show that the period analysis results of the three drought indexes were consistent, and they all presented a major period of 22-25 years and a secondary period of 5-10 years; SPI and Pa were more significant in reflecting changes of short-term period. Result of the mutation point test based on Mann-Kendall test and moving T test showed that mutation point was around 1978 according to modified Palmer Index, while around 1986 according to the other two indexes. As a whole, these three indexes basically showed the same drought tendency, however, under high temperature variation and actual evaporation, the modified Palmer Index can more accurately characterize the drought-flood grades, temperature change response and drought-flood duration. Since the drought and flood formation not only has high correlations with precipitation, solar radiation and relative moisture, but also may relate to unusual weather events, tropical ocean temperature anomaly, and the influence of human activities on the drought and flood situation which was not taken into consideration in revising Palmer index in this paper, further research is expected to be focused on a combination of factors analyzed in depth.

Key words: modified Palmer Index, standardized precipitation index, precipitation anomaly percentage, Huang-Huai-Hai River Basin