Why East Coasts Lack Deserts (Usually)

Rather than seeing consistent “band of deserts” in the subtropics on our planet, we actually see a major asymmetry: subtropical deserts are almost always absent from eastern coastlines. This is true in North America, South America, Australia, Southern Africa, and Australia. In general, rainfall is much greater on the eastern side of a landmass at subtropical latitudes. Why do we see this pattern? Why are eastern coastlines, at subtropical latitudes, usually much more humid? This is critical to understanding the geography of deserts. Image Sources: Arizona State University Wikipedia Creative Commons (Shwollo) Google Earth earth.nullschool.net NASA Information Sources: Nicholson, S. E. (2011). Dryland Climatology. United Kingdom: Cambridge University Press. Ahrens, C. D. (2013). Meteorology Today (10th ed., pp. 490-492). Brooks/Cole, Cengage Learning. Koster, R., Jouzel, J., Suozzo, R., Russell, G., Broecker, W., Rind, D., & Eagleson, P. (1986). Global sources of local precipitation as determined by the Nasa/Giss GCM. Geophysical Research Letters, 13(2), 121–124. doi:10.1029/gl013i002p00121  Zemp, D. C., Schleussner, C.-F., Barbosa, H. M. J., van der Ent, R. J., Donges, J. F., Heinke, J., … Rammig, A. (2014). On the importance of cascading moisture recycling in South America. Atmospheric Chemistry and Physics, 14(23), 13337–13359. doi:10.5194/acp-14-13337-2014  Ampuero, A., Stríkis, N. M., Apaéstegui, J., Vuille, M., Novello, V. F., Espinoza, J. C., … Siffedine, A. (2020). The forest effects on the isotopic composition of rainfall in the northwestern Amazon Basin. Journal of Geophysical Research: Atmospheres. doi:10.1029/2019jd031445  Yang, Z., & Dominguez, F. (2019). Investigating land surface effect on the moisture transport over South America with a moisture tagging model. Journal of Climate. doi:10.1175/jcli-d-18-0700.1  A New Look into the South America Precipitation Regimes: Observation and Forecast. Glauber W. S. Ferreira. Michelle S. Reboita. Atmosphere 2022, 13(6), 873; https://doi.org/10.3390/atmos13060873 Rocha, V. M., Da Silva, P. R. T., Gomes, W. B., Vergasta, L. A., & Jardine, A. (2018). Precipitation Recycling in the Amazon Basin: A Study Using the ECMWF Era-Interim Reanalysis Dataset. Geography Department University of Sao Paulo, 35, 71–82. doi:10.11606/rdg.v35i0.139494  Agel, L., Barlow, M., Qian, J.-H., Colby, F., Douglas, E., & Eichler, T. (2015). Climatology of Daily Precipitation and Extreme Precipitation Events in the Northeast United States. Journal of Hydrometeorology, 16(6), 2537–2557. doi:10.1175/jhm-d-14-0147.1  eumetrain.org. (2012). Cyclogenesis and Extra-tropical Cyclones Over Southeastern South America. Meteorological Satellite Data Training. https://resources.eumetrain.org/satmanu/CM4SH/BrCg/index.htm Monthly Wind Climatology. Climate Monitoring Technologies, Columbia University. https://iridl.ldeo.columbia.edu/maproom/Global/Climatologies/Vector_Winds.html