Persistent drying in the tropics linked to natural forcing

Abstract

Approximately half of the world's population lives in the tropics, and future changes in the hydrological cycle will impact not just the freshwater supplies but also energy production in areas dependent upon hydroelectric power. It is vital that we understand the mechanisms/ processes that affect tropical precipitation and the eventual surface hydrological response to better assess projected future regional precipitation trends and variability. Paleo-climate proxies are well suited for this purpose as they provide long time series that pre-date and complement the present, often short instrumental observations. Here we present paleo-precipitation data from a speleothem located in Mesoamerica that reveal large multi-decadal declines in regional precipitation, whose onset coincides with clusters of large volcanic eruptions during the nineteenth and twentieth centuries. This reconstruction provides new independent evidence of long-lasting volcanic effects on climate and elucidates key aspects of the causal chain of physical processes determining the tropical climate response to global radiative forcing.

Speleothem Paleoclimatology for the Caribbean, Central America, and North America

“…There is also evidence for the influence of aerosol forcing by volcanic and human activity on Mesoamerican rainfall variability from Belize [140,141]. Both studies provide evidence of long-lasting volcanic effects on precipitation changes in Mesoamerica during the past centuries.…”

“…Both studies provide evidence of long-lasting volcanic effects on precipitation changes in Mesoamerica during the past centuries. However, the authors also note, that direct climate effects cannot be attributed to volcanic aerosol forcing alone, but may have exacerbated or prolonged the drought intervals beyond the duration of the direct radiative imbalance [140][141][142]. In summary, this makes interpretation of precipitation-proxy records as large-scale rainbelt movement challenging, requiring regional or global data syntheses.…”

Initiation of a stable convective hydroclimatic regime in Central America circa 9000 years BP

“…In Central America the marked heterogeneity of modern hydroclimate regimes arises from interacting atmospheric, oceanic, and land processes that occur in this narrow stretch of land separating the tropical Pacific and tropical North Atlantic oceanic basins [8][9][10][11][12] . The same processes explain the strong sensitivity of this region to external forcing.…”

“…The same processes explain the strong sensitivity of this region to external forcing. Stalagmite records suggest that externally forced multidecadal anomalies in Atlantic and Pacific sea-surface temperatures (SSTs) significantly made an imprint on Central American rainfall evolution throughout the past few centuries 8 . Model projections 13 under global warming scenarios suggest that a similar chain of mechanisms may be responsible for a potential substantial drying of more than 30% over Central America.…”

Response File for All Reviews

“…George, 2014;St. George and Ault, 2014;Wise and Dannenberg, 2014;Anchukaitis et al, 2017;Baek et al, 2017). The network itself is biased toward terrestrial middle and high latitudes in the Northern Hemisphere (NH), reflecting a mix of historical focus, continental forest regions, and the abundance of trees that form unambiguous annual growth rings.…”