四分律行事鈔資持記 3.627

3.627

《十誦》。多雨處，四月在露，即冬分也；八月在覆，春夏雨多也。少雨反前者，冬春八月在露，夏四月在覆。

The Daśādhyāya-vinaya: In places with much rain, four months are in the open, which is the winter period; eight months are under cover, because rain is plentiful in spring and summer. Where there is little rain, it is the reverse of the former: eight months of winter and spring are in the open, and the four months of summer are under cover.