Global sources of local precipitation as determined by the Nasa/Giss GCM

The origin of water precipitating in different geographic regions is investigated with the NASA/GISS GCM. Water evaporating from various source regions is "tagged" and then followed as a tracer in four model simulations, one for each season. The contributions of source region evaporations to simulated rainfall at specific locations is tabulated. The results show that in the summer, water vapor for midlatitude and high latitude precipitation tends to be recycled locally, whereas low latitude continental precipitation is more dependent on oceanic moisture sources.