Floods from above and below: Insights beyond increases in daily precipitation extremes over flat agricultural plains

Abstract

While increasing flood occurrence due to climate change is typically linked to increases in extreme daily precipitation, as in the Intergovernmental Panel on Climate Change (IPCC)’s Sixth Assessment Report, stagnant hydrological plains can have flood regimes that respond to longer term water balance shifts rather than extreme events. We use observational data on precipitation, water table height, and flooded area as well as reports from local agencies to study flooding over the stagnant agricultural plains of the Argentinean Pampas, where the precipitation regime has not changed during the last several decades. Increases in daily extreme precipitation therefore cannot explain the observed increase of flooding. Furthermore, our results show that, during the period 1986–2020, monthly precipitation extremes are not significantly associated with floods and water table height. However, we show that floods and water tables have become more reactive to seasonally accumulated precipitation during the last two decades.