Regime shift of global oceanic evaporation in the late 1990s using OAFlux dataset

Abstract

After the decadal change being marked by a distinct transition from a downward trend to an upward trend around 1977–1978, the global oceanic evaporation is found to present a regime shift to downward trend from 2000 onwards by using the Objectively Analyzed air-sea Fluxes (OAFlux) dataset. The robustness of post-2000 decreasing trend of global oceanic evaporation featured by OAFlux is fairly confirmed by checking the total precipitation trend from the Global Precipitation Climatology Project (GPCP) and the CPC Merged Analysis of Precipitation (CMAP) datasets via budget constraint. Analysis on the 1999/2000 trend reversal in global mean temporal evolution and local linear trend patterns of evaporation and related variables is performed. Results show that the positive trend of evaporation before 2000 is primarily associated with both the SST warming and the strengthening of near-surface wind, while the negative trend of evaporation after 2000 may be highly correlated with the weakening of near-surface wind speed and reduction in sea-air humidity difference. The post-2000 decreasing of oceanic evaporation mainly effects precipitation trend over oceans via budget constraint, while land precipitation shows no significant decreasing trend, which may be explained by the increasing of evapotranspiration over land.