Influence of Vegetation on Rainy Season Onset and Its Predictability

Abstract:

The conventional wisdom attributes rainy season onset over land to the reversal of the land-ocean surface temperature gradient, and resultant moisture transport from ocean to land, especially over the monsoon regions. However, this mechanism cannot explain rainy season onset over humid tropical continents where such surface temperature gradient reversal is absent, and the delayed rainy season onset that is often proceeded by anomalous dry land surface in absence of persistent oceanic forcing. In the past several decades, evidence for the influence of vegetation seasonality on rainy season onset, its variability and predictability has been emerging, enabled by advancement of ground-based and remote sensing observational capabilities. In this presentation, I will give observational evidence for the active role that vegetation seasonality plays in determining the rainy season onset and strength, and in modulating oceanic influences on continental rainfall, especially in providing deep memory and potentially predictability, for rainfall variability on seasonal to interannual time scales and ranging from humid tropical and semi-arid subtropical continents.