Closure of the Water Budget over Tropical Oceans – Intra-Annual Variability

A large number of studies have focused on quantifying the water and energy balance over global and, more recently, even regional scales. Few studies, however, have looked at temporal variations in the water budget to assess the impact of large-scale atmospheric variability on our estimates of the precipitation, evaporation and water vapor divergence. We use the Global Water and Energy Experiment (GEWEX) integrated product for the water and energy variables on 1°, 3hr scales. These are GPCP V2.3 for precipitation, SeaFlux for evaporation and ERA5 for water vapor divergence. Using these products, we examined the water budget closure over 6 distinct tropical ocean basins, including the western and eastern Indian oceans, the western, central and eastern Pacific, and the Atlantic. It was found that the water imbalance in the Indian ocean is largely explained by potential errors in evaporation stemming from an underestimated evaporation during periods of high surface wind speeds. Over the western Pacific, changes in convective organization during the annual cycle seem to affect precipitation estimates to explain the potential lack of closure. Lack of closure in the central Pacific appears to be explained by water vapor divergence from ERA5 while the eastern Pacific issues appear related to near-surface moisture deficits. The Atlantic is rather well balanced throughout the year. Thus, while no single parameter explains the lack of water budget closure, the observed issues can be related to annual changes in the large-scale circulation and progress can be made – even without detailed validation studies in each of the basins.