The number of poor men is on the decrease as the economy is growing.

随着经济发展，贫困人口数量正在减少。

The birthrate is on the decrease.

人口出生率正在下降。

Is crime on the decrease?

犯罪的案件是否在减少中？

The population of this city is on the decrease.

这个城市的人口正逐渐减少。