关键词: 旱涝, 旱涝指数, 周期模式法

Abstract: Water supplement is very important in Beijing where drought has frequently occurred since the 1960s. The climatic prospect about drought or flood is studied in this paper. The study will focus the attention on three problems: first, how is the climate situation about dryness and wetness described? Second, how do they vary with time? Third, which method will be better for forecasting them? The yearly dryness/wetness index for describing climate situation is proposed in this pa-per. It is the sum over twelve证the monthly moisture index which is the standardized mon-thly precipitation. It is more meaningful a.nd representative than the index of yearly preci-pitation. The series of the yearly dryness/wetness index in Beijing for the period from 1869 to 1987 have been built. Furthermore, it is investigated using power spectral analysis and variance analysis for its characteristics of the periodic variation, and is found that the main periods are 5-yr and 2Z-yr. The period patterns, for 5-yr and 22-yr are extracted. by means of the period pattern method proposed in this paper. The patterns are represented by the eigenvectors of the cross-product matrix of the period matrix whose elements are from the original series arranged as an array according to the length of the period. The forecasting of the dryness/wetness index is completed through the regression equation in which the period patterns are considered as the predictors. The results show that the water supplement wi}1t probably get improvement in Beijing by the end of this century.

Key words: Drought and flood, The dryness/wetness index, The period pattern me-thod