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Robust Responses of the Sahelian Hydrological Cycle to Global Warming

Hill, Spencer A. and Ming, Yi and Zhao, Ming (2018) Robust Responses of the Sahelian Hydrological Cycle to Global Warming. Journal of Climate, 31 (24). pp. 9793-9814. ISSN 0894-8755. http://resolver.caltech.edu/CaltechAUTHORS:20181205-145455777

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Abstract

How the globally uniform component of sea surface temperature (SST) warming influences rainfall in the African Sahel remains insufficiently studied, despite mean SST warming being among the most robustly simulated and theoretically grounded features of anthropogenic climate change. A prior study using the NOAA Geophysical Fluid Dynamics Laboratory (GFDL) AM2.1 atmospheric general circulation model (AGCM) demonstrated that uniform SST warming strengthens the prevailing northerly advection of dry Saharan air into the Sahel. The present study uses uniform SST warming simulations performed with 7 GFDL and 10 CMIP5 AGCMs to assess the robustness of this drying mechanism across models and uses observations to assess the physical credibility of the severe drying response in AM2.1. In all 17 AGCMs, mean SST warming enhances the free-tropospheric meridional moisture gradient spanning the Sahel and with it the Saharan dry-air advection. Energetically, this is partially balanced by anomalous subsidence, yielding decreased precipitation in 14 of the 17 models. Anomalous subsidence and precipitation are tightly linked across the GFDL models but not the CMIP5 models, precluding the use of this relationship as the start of a causal chain ending in an emergent observational constraint. For AM2.1, cloud–rainfall covariances generate radiative feedbacks on drying through the subsidence mechanism and through surface hydrology that are excessive compared to observations at the interannual time scale. These feedbacks also act in the equilibrium response to uniform warming, calling into question the Sahel’s severe drying response to warming in all coupled models using AM2.1.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1175/jcli-d-18-0238.1DOIArticle
https://journals.ametsoc.org/doi/suppl/10.1175/JCLI-D-18-0238.1DOISupporting Information
ORCID:
AuthorORCID
Hill, Spencer A.0000-0001-8672-0671
Zhao, Ming0000-0002-4258-9517
Additional Information:© 2018 American Meteorological Society. . For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses). Denotes content that is immediately available upon publication as open access. (Manuscript received 18 April 2018, in final form 7 September 2018) We thank Fanrong Zeng and Larry Horowitz of GFDL for performing the extended AMIP simulations in AM2.1 and AM3, respectively; Isaac Held and Leo Donner for helpful discussions; Bill Boos, Nadir Jeevanjee, Kirsten Findell, and three anonymous reviewers for their insightful reviews of earlier drafts; the “ana4mips” project for providing all reanalysis data used; and Spencer Clark for his work on the “aospy” data analysis package (Hill and Clark 2017) used for a majority of the calculations. S.A.H. was supported first by a Department of Defense National Defense Science and Engineering Graduate Fellowship and subsequently by a National Science Foundation Atmospheric and Geospace Sciences Postdoctoral Research Fellowship (Award 1624740). Supplemental information related to this paper is available at the Journals Online website: https://doi.org/10.1175/JCLI-D-18-0238.s1.
Funders:
Funding AgencyGrant Number
National Defense Science and Engineering Graduate (NDSEG) FellowshipUNSPECIFIED
NSF Postdoctoral FellowshipAGS-1624740
Subject Keywords:Atmosphere; Africa; Rainfall; Sea surface temperature; Climate change; Climate models
Record Number:CaltechAUTHORS:20181205-145455777
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20181205-145455777
Official Citation:Hill, S.A., Y. Ming, and M. Zhao, 2018: Robust Responses of the Sahelian Hydrological Cycle to Global Warming. J. Climate, 31, 9793–9814, https://doi.org/10.1175/JCLI-D-18-0238.1
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91520
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:05 Dec 2018 23:14
Last Modified:05 Dec 2018 23:14

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