E please help me to transform the sentence to english 通过不同的阈值对SDSI划分等级在所有的河口复合干咸事件中moderate复合事件发生的频率最高Exceptional复合干咸事件的频率最小。SDSI发生严重复合干咸事件的频率如Severe Extreme Exceptional大于单一SRI指数。

By using different thresholds to classify SDSI levels, moderate compound events occur most frequently among all estuarine compound dry-salty events, while the frequency of Exceptional compound dry-salty events is the lowest. The frequency of severe compound dry-salty events (such as Severe, Extreme, Exceptional) in SDSI is higher than that of a single SRI index.