The precipitation in northwest China had a significantly increasing trend (P < 0.01) for annual rainfall, at a rate of 0.55 mm/a.

It is not necessarily that while the periodic components have significant trends, the original data also have.

The drivers from periodic component of original data was different from season to season, and different from area to area.

Most of the trends, whether positive or negative, started during the mid − 1980s to mid − 1990s.

The relationships between the precipitation and SST are different for different periodic components and different periods.