Interannual variability of the sources of warm-season precipitation over the Mississippi basin

Water falling as rain over the Mississippi basin is supplied by local and remote surface evaporation, both terrestrial and oceanic. Using event-based back-trajectory analysis, we have mapped the surface evaporative sources for precipitation to the Mississippi and its five major sub-basins over a 36-year period. The results are aggregated into estimates of precipitation supplied by various source regions (the basin itself, Southwest U.S., Gulf of Mexico, Caribbean, Pacific, etc.) on a pentad, monthly, and seasonal basis. Principal component analysis indicates strong continental control on the interannual variability of total precipitation to the Mississippi basin. The relative contributions of some of the source regions to warm-season precipitation are correlated with remote sea surface temperature indices (ENSO and PDO), suggesting connections to planetary-scale climate fluctuations.