Assessing and QUantifying the ATlantic Instrumental hydroClimate

Precipitation (P) and runoff (R) variability around the tropical and subtropical Atlantic is of fundamental importance to the biosphere and carbon system, and to human livelihood.

Over recent decades, decadal variations in P and R — including droughts in the Sahel region of West Africa, northeast Brazil, the Caribbean, and the Amazon basin — have caused large social and economic disruptions.

However, understanding the causes of these events, as well as projecting regional 21st century climate change hydroclimate impacts, are complicated by the relative shortness in the instrumental record, which reduces confidence in the attribution of external forcings.AQUATIC will extend the record of Atlantic-sector hydroclimate variability during the 1880–1950 period.

We will: (1) compile an integrated hydroclimate dataset including newly-recovered P station gauge data, long-term river R measurements, and a unique long-term record of Atlantic sea surface salinity which we will use as an “ocean rain gauge” to infer the surface evaporation (E)–P–R balance.

We will then (2) examine these integrated hydroclimate data along with atmospheric and ocean reanalysis output to characterize mechanisms of decadal-to-multidecadal hydroclimate variability, including shifts of the intertropical convergence zone (ITCZ) and expansion and contraction of the Hadley circulation.

This will allow us to (3) evaluate the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations to attribute long-term hydrological change to different external forcings, and constrain future climate projections.AQUATIC will combine analysis of early instrumental historical climate data with state-of-the-art reanalysis and model output to understand mechanisms of hydroclimate variability in and around the Atlantic and to narrow uncertainties for the future in this climatologically important region.