Untangling the importance of dynamic and thermodynamic drivers for wet and dry spells across the Tropical Andes

Cornelia Klein*, Lorenz Hänchen, Emily R. Potter, Clémentine Junquas, Bethan L. Harris, Fabien Maussion

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review


Andean vegetation and agriculture depend on the patterns of rainfall during the South American monsoon. However, our understanding on the importance of dynamic (upper-level wind circulation) as compared to thermodynamic (Amazon basin moisture) drivers for Andes rainfall remains limited. This study examines the effect of these drivers on 3-7 day wet and dry spells across the Tropical Andes and assesses resulting impacts on vegetation. Using reanalysis and remote sensing data from 1985-2018, we find that both dynamic and thermodynamic drivers play a role in determining the rainfall patterns. Notably, we show that the upper-level wind is an important driver of rainfall across the entire Tropical Andes mountain range, but not in the Amazon lowlands, suggesting a crucial role of topography in this relationship. From thermodynamic perspective, we find wet spell conditions to be associated with increased moisture along the Andes’ eastern foothills accompanied by a strengthened South American low-level jet, with moisture lifted into the Andes via topography and convection for all considered regions. Our results suggest that while changes in Amazon basin moisture dominate rainfall changes on daily time scales associated with three day spells, upper-level dynamics play a more important role on the synoptic time scale of 5-7 day spells. Considering impacts on the ground, we find that only 5-7 day spells in the semi-arid Andes have a prolonged effect on vegetation. Our study emphasizes the need to consider both dynamic and thermodynamic drivers when estimating rainfall changes in the Tropical Andes, including in the context of future climate projections.

Original languageEnglish
Article number034002
JournalEnvironmental Research Letters
Issue number3
Publication statusPublished - 13 Feb 2023

Bibliographical note

Funding Information:
The research leading to these results was conducted within the AgroClim-Huaraz project ( https://agroclim-huaraz.info/ ), which received funding from the Österreichische Akademie der Wissenschaften. CK also acknowledges funding from the NERC-funded LMCS project (NE/W001888/1). We thank the providers of key data sets used here. GRIDSAT-1B is available from www.ncdc.noaa.gov/gridsat , ECMWF ERA5 reanalysis data is available from the Copernicus Data Store ( https://cds.climate.copernicus.eu/ ), CHIRPS data are available from www.chc.ucsb.edu/data/chirps , VOD data from https://doi.org/10.5281/zenodo.2575599 , soil moisture data from www.esa-soilmoisture-cci.org/v06.1_release , BESS data (for PAR) from www.environment.snu.ac.kr/bess-rad , CSIFv2 (for SIF) data from https://osf.io/8xqy6/ and MODIS MCD43A4v061 (for NIRv) data were acquired via AppEEARS https://appeears.earthdatacloud.nasa.gov/ . Special thanks go to the providers of the python packages matplotlib/cartopy, xarray, salem, scipy, metpy, and their dependencies.

Publisher Copyright:
© 2023 The Author(s). Published by IOP Publishing Ltd.


  • dry spells
  • rainfall drivers
  • Tropical Andes
  • vegetation
  • wet spells


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