Environmental Science Humid Tropical Environments
Richard Corlett
  • LAST REVIEWED: 30 July 2019
  • LAST MODIFIED: 28 April 2016
  • DOI: 10.1093/obo/9780199363445-0050


Humid tropical environments cover a relatively minor part (c. 8 percent) of the earth’s total land surface area, but support most of the world’s terrestrial biodiversity, as well as large and rapidly increasing human populations, and play critical roles in global water and carbon cycles. The use of the word “humid” is unfortunate since high humidity is not the most important characteristic of these environments, but it is the one most obvious to visitors from outside the tropics. Alternatives, such as “wet,” “moist,” “aseasonal,” and “equatorial” have been used more or less interchangeably, but none of these are as common. Humid tropical environments are concentrated within 5⁰ to 10⁰ of the equator, but topography, sea surface temperatures, and other factors create gaps in this equatorial humid belt while extending it further north or south in other places. The key feature is absence of a water deficit for most of the year, which means biological and geomorphic processes that require accessible moisture can occur without interruption. However, there is no generally accepted definition, and usage varies quite widely. There is probably nowhere in the tropics that never experiences a biologically significant water deficit, if only at multiyear intervals, and brief (one to three month) annual dry periods synchronize biological activity without having a large impact on the appearance of the vegetation. This article therefore follows the most common contemporary usage in applying the term “humid tropics” to any region that can support closed-canopy forests (plus alpine areas above a tropical treeline) and in excluding areas that would naturally be covered in savanna, grassland, or desert. Humid tropical environments are contrasted with arid ones, where there are overall water deficits, but these environments form the ends of a continuum, with intermediate environments variously described as subhumid, monsoonal, wet-dry, and semi-arid. This article focuses on ecology but also covers the physical environment and human-environment interactions.

General Overviews

Most recent books on the humid tropics as a whole have focused on only one aspect, such as the vegetation, but Reading, et al. 1995 provides a broad, readable, textbook-level overview. The State of the Tropics: 2014 Report is part of an on-going project assessing the current states of both human and natural systems in the tropics, making it a useful source of information on topics that are not covered in any other recent publication.

  • Reading, A., A. C. Millington, and R. D. Thompson. 1995. Humid tropical environments. Oxford: Wiley-Blackwell.

    This textbook introduces the weather, climates, soils, vegetation, hydrology, resources, and problems in the humid tropics. It is targeted at geographers, but the broad overview is useful for anyone working in these environments.

  • State of the tropics: 2014 report. 2014. Cairns, Australia: James Cook Univ.

    This data-packed report explores environmental, social, and economic indicators in order to answer the question, “Is life in the tropics getting better?” The answer is yes, on the whole, although massive problems remain.

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