基于概率矩阵的干旱等级变化评估及应用

干旱等级具有多级和跃迁性质，有必要提出一种既能反映不同干旱等级变化特征，又能体现干旱总体变化特征的定量评估方法。通过构建干旱等级变化的概率矩阵，引入变化率乘子和变化程度乘子，推导干旱等级变化率和变化程度计算公式，提出干旱等级变化的综合定量评估方法；借助标准化降水蒸散指数和标准化径流指数，应用于东江流域评估月、季和年尺度的气象干旱向水文干旱传递过程中干旱等级变化及水库影响下水文干旱等级变化。结果表明:①气象干旱向水文干旱传递过程中干旱总体变化程度较小，但干旱等级变化明显，月、季和年尺度的总体变化率分别达到了45.9%、46.8%和34.9%；②干旱在10月下降了约1.4个等级，在春季上升了约1.3个等级；③水库径流调节对于缓解月、季尺度水文干旱作用显著，干旱等级总体变化率均约为33%，其中春季干旱程度下降了约1个等级。该方法不仅适用于评估干旱变化，也可应用于评估具有分级特征的其他灾害变化。

An evaluation method for drought level changes based on probability matrix and its application

Drought levels are multi-level and transitional. A method quantitatively evaluating changes in drought levels and overall changes in drought are needed. By constructing a probability matrix of drought level change and introducing the multipliers of rate and degree of change, this study derived their formulas and developed a quantitative method for evaluation of drought level change. Standardized precipitation-evapotranspiration index and standardized streamflow index were employed to analyze drought levels in the Dongjiang River basin as an example. Changes in drought levels from meteorological drought to hydrological drought and those in hydrological drought levels under the influence of reservoirs regulation were evaluated at monthly, seasonal and annual scales. Results showed that: ① The degree of overall change in drought was small, but the change in drought level was distinct. The rates of overall change in drought levels at monthly, seasonal and annual scales were 45.9%, 46.8%, and 34.9%, respectively. ② The change in drought level decreased by approximately 1.4 level in October, but increased by 1.3 level in Spring. ③ The impact of reservoir regulation on the hydrological drought was significant at monthly and seasonal scales. The rate of overall change in drought level was 33% and the drought level decreased approximately by one level in spring. The proposed method can be applied not only for drought evaluation, but also for the assessment of other disasters.