Relatively clean snow and ice in the Indus River Basin during the COVID-19 pandemic may have reduced meltwater in 2020, compared with the 20-year average.
Image credit: Pixabay/Abdullah_Shakoor.
Edited by Mark H. Thiemens, University of California at San Diego, La Jolla, CA, and approved June 14, 2017 (received for review January 3, 2017)
Significance
This analysis provides compelling observational evidence that rainforest transpiration during the late dry season plays a central role in initiating the dry-to-wet season transition over the southern Amazon. Transpiration first activates shallow convection that preconditions the atmosphere for regional-scale deep convection, rather than directly activating deep convection as previously proposed. Isotopic fingerprints in atmospheric moisture unequivocally identify rainforest transpiration as the primary moisture source for shallow convection during the transition. This “shallow convection moisture pump” thus depends on high transpiration rates during the late dry season, affirming the potential for climate and land use changes to alter or disrupt wet season onset in this region.
Abstract
Although it is well established that transpiration contributes much of the water for rainfall over Amazonia, it remains unclear whether transpiration helps to drive or merely responds to the seasonal cycle of rainfall. Here, we use multiple independent satellite datasets to show that rainforest transpiration enables an increase of shallow convection that moistens and destabilizes the atmosphere during the initial stages of the dry-to-wet season transition. This shallow convection moisture pump (SCMP) preconditions the atmosphere at the regional scale for a rapid increase in rain-bearing deep convection, which in turn drives moisture convergence and wet season onset 2–3 mo before the arrival of the Intertropical Convergence Zone (ITCZ). Aerosols produced by late dry season biomass burning may alter the efficiency of the SCMP. Our results highlight the mechanisms by which interactions among land surface processes, atmospheric convection, and biomass burning may alter the timing of wet season onset and provide a mechanistic framework for understanding how deforestation extends the dry season and enhances regional vulnerability to drought.
Footnotes
- ↵1To whom correspondence should be addressed. Email: rfu{at}atmos.ucla.edu.
↵2Present address: School of Integrative Plant Science, Soil and Crop Sciences Section, Cornell University, Ithaca, NY 14853.
Author contributions: R.F. designed research; J.S.W. performed research; J.S.W., J.R.W., S.C., N.E.C., C.R., Y.S., and L.Y. analyzed data; and J.S.W. and R.F. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1621516114/-/DCSupplemental.
Rainforest-initiated wet season onset
Article Classifications
- Physical Sciences
- Environmental Sciences
Sign up for Article Alerts
Jump to section
You May Also be Interested in
Atmospheric and climate conditions could have created a cloud greenhouse effect to warm Mars and support liquid surface water.
Image credit: NASA/JPL/MSSS.
Researchers report a safety guideline to limit airborne transmission of COVID-19 that goes beyond the six-foot social distancing guideline.
Image credit: Pixabay/Matryx.
What if we stopped using oil and gas as fuels and instead use them as sources of both hydrogen for fuel and carbon for useful, pervasive materials?
Nanotube image credit: Shutterstock/Gl0ck; Field image credit: Shutterstock/Evgeny Karandaev.
The protein's capacity to fold into multiple conformations is reminiscent of a prion.
Image credit: Science Source/Dennis Kunkel.