The 2005 Amazon Drought Legacy Effect Delayed the 2006 Wet Season Onset

While the long‐term drought effect on tropical forests has been observed in ground‐based and remote sensing measurements, the feedback of reduced forest biomass on subsequent rainfall is not well understood. We evaluate the impact of slow forest recovery after the 2005 Amazonian drought on local evapotranspiration (ET) and wet season onset (WSO) using remotely sensed precipitation, deuterium retrievals, reanalysis data, and a new ET product. A comparison to the 2009 rainy season, which exhibits similar large‐scale moisture flux convergence, shows that 2006 experienced a 25% ET reduction and 20 days of postponed WSO in the dry‐to‐wet transition. Our results imply that ET reduction due to drought‐driven legacy effect on the Amazon rainforest could be a crucial factor triggering WSO delay in the transitional season following drought events. Plain Language Summary Drought legacy effect, observed as reduced growth and incomplete forest recovery after severe drought events, impacts the carbon and water cycles of Amazonia. Satellite observations showed a reduction of canopy carbon during and after the 2005 Amazonian drought. To understand the impact of local evapotranspiration (ET) changes associated with this canopy carbon reduction on the timing of wet season onset (WSO) over southern Amazonia, we study the precipitation and ET changes in the 2006 dry‐to‐wet transition by using space‐based remote sensing of precipitation, deuterium retrievals, reanalysis data, and a new ET product. A comparison to the 2009 rainy season, which has a similar large‐scale moisture flux convergence amount, shows a 25% reduction in ET and 20 days of postponed WSO during the dry‐to‐wet transition of 2006. Our results indicate that drought legacy effects could be a crucial factor triggering WSO delay following drought events and imply the importance of accurately representing biogeochemical processes and land‐atmosphere feedbacks when predicting precipitation over Amazon in Earth system models.