Monitoring extreme floods and droughts in the Amazon basin with surface water based indices

Extreme droughts and floods in the Amazon have great implications for ecosystems and societies. Over the last decade, the region has undergone major extreme events with no equivalent in the previous 100 years. Wetlands have been greatly impacted by these events. This study aims at presenting new indicators for wetlands based on Water Surface Extent (WSE): duration of the flooded and non-flooded season, number of days of extreme events, delay of the start of the flooded season, and severity for each season. These indicators are more adapted for monitoring of wetlands than those based on precipitation, discharge or groundwater information. They are computed for seven major Amazon sub-basins for flooded and non-flooded seasons. These indicators improve our knowledge of the temporal behavior of water surface during different extreme events, such as the 2015/2016 drought and the 2014 flood occurred in the Madeira basin. For the Negro basin and from the point of view of wetlands, the 2015 non-flooded season was 55% more severe than the average of the non-flooded season during the 2011-2018 period. For the Paru, Trombetas, Negro and Solimões basins, we found that a delay in the arrival of the flooded season led to a weak flood season in terms of severity. No correlation between the onset of the flooded season and its severity was found for the Madeira, Xingu and Tapajós basins. Future hydrometeorological monitoring systems would benefit from including, in addition to variables such as river discharge and water elevation, precipitation and vegetation dynamics, a severity index based on water surfaces as proposed in this study.