Spatial Extents of Tropical Droughts During El Niño in Current and Future Climate in Observations, Reanalysis, and CMIP5 Models. Issue 14 (26th July 2021) - Perez Arango, Juan D.
Abstract: Drought conditions significantly impact human and natural systems in the Tropics. Here, multiple observational and reanalysis products and ensembles of simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analyzed with respect to drought areal extent over tropical land regions and its past and future relationships to the El Niño/Southern Oscillation (ENSO). CMIP5 models forced with prescribed sea surface temperatures compare well to observations in capturing the present day time evolution of the fraction of tropical land area experiencing drought conditions and the scaling of drought area and ENSO, that is, increasing tropical drought area with increasing ENSO warm phase (El Niño) strength. The ensemble of RCP8.5 simulations suggests lower end‐of‐the‐century El Niño strength‐tropical drought area sensitivity. At least some of this lower sensitivity is attributable to atmosphere‐ocean coupling, as historic coupled model simulations also exhibit lower sensitivity compared to the observations. Plain Language Summary: Many regions of the planet are extremely vulnerable to drought. In the tropics, the El Niño/Southern Oscillation (ENSO) phenomenon is recognized as a key driver of drought occurrence. In this study, we analyze the spatial extent of droughts over tropical land regions and evaluate its connection to ENSO in the recent past in observations and current generation models as well as simulated future projections. We demonstrate overall model fidelity in capturing a positive relationship between the tropical land area under drought and El Niño in the recent past and consider how this relationship may change in the future. Key Points: Observed and model‐simulated tropical land region drought areal extents reflect similar temporal evolution Tropical land region drought area increases with increasing strength of El Niño The apparent decrease in future ENSO‐tropical drought area sensitivity appears to arise in part from atmosphere‐ocean coupling