Decreased rainfall in northern areas is due to

Decreased rainfall in northern areas is due to deforestation in evaporating areas near equator.
Deforestation also contributes to decreased evapotranspiration, which lessens atmospheric moisture which in some cases affects precipitation levels downwind from the deforested area, as water is not recycled to downwind forests, but is lost in runoff and returns directly to the oceans.
According to one study, in deforested north and northwest China, the average annual precipitation decreased by one third between the 1950s and the 1980s.