Contents - Next

This is the old United Nations University website. Visit the new site at


The United Nations University project Climatic, Biotic, and Human Interactions in the Humid Tropics was initiated as part of the University's programme on Resource Policy and Management to investigate the interactions between forest cover and critical climatological and biogeochemical parameters in the humid tropics. Considering the abundance of speculation and anxiety with regard to the impact of human activity on the earth's climate and biosphere, the need was strongly felt for more scientific information on biotic and climatic interactions to more accurately determine the actual nature and extent of human inflicted damage to environmental systems.

The present study arose from a workshop whose aim was to evaluate existing evidence of the ecological impact of deforestation and afforestation on regional climate and hydrology. This volume makes a clear case for the need for an objective and quantitative assessment of the effects of vegetation on climate and hydrology and their regional extent.


The workshop Forests, Climate, and Hydrology: Regional Impacts and this book resulting from it are central to the programme area on Resource Policy and Management of the United Nations University. In the first place the subject embraces these vital world resources on which hinges the development of so many nations. Only by understanding the interactions of these resources can they be conserved and used rationally for the good of mankind. Human well being depends on, among other things, adequate supplies of wood and water, but what is the effect of man's husbandry of the earth's surface on these vital resources and even on the climate itself? Even if the answer from this workshop were a qualified "None," then this could be taken into account in the land use policies of developing countries.

UNU involvement is apt in the second place because of the international nature of the subject. Not only did the workshop consist of experts from more than 10 countries but serious consideration was given to the possibility of large-scale vegetation changes induced by man in one country producing some climatic effects in other countries of that region or even on a global scale. Ignorance of such effects, their magnitude and scale, could result in international tensions. International collaboration in these studies is vital both in collecting the relevant data and in carrying out the large-scale computer operations needed to simulate the effects of land use changes on regional and global circulation and climate.

Thirdly the workshop falls squarely within the UNU remit in being interdisciplinary. Experts on vegetation, earth surface hydrology, and microclimate need to be brought together with physicists concerned with large-scale atmosphere dynamics. So complex is the field that no single country has adequate resources to cover it all sufficiently, but the UNU was able to bring together the various specialists from all six continents.

Currently land use changes in developed countries are relatively small-scale from a climatic viewpoint; the greatest changes are occurring in the developing countries, especially those of the tropics and subtropics. Therefore the workshop paid particular attention to the relations between tropical moist forests and atmospheric circulation. These are also regions of greater emphasis in the current UNU programme on Climatic, Biotic, and Human Interactions in the Humid Tropics.

For these reasons I feel sure that this book will promote the objectives of the UNU, not only by informing the scientific community of the synthesis reached by the workshop and by injecting some timely suggestions on the ramifications of land use policies but also by stimulating investigators to bring forward critical projects that will advance our knowledge in the vital area of the effect on the climate of this planet by man's modification of its vegetation.

United Nations University


The United Nations University has contributed notably to the subject area of the possible repercussions of land use change on climate in sponsoring the workshop (at St. John's College, Oxford, 25-30 March 1984) that has resulted in this publication. The initiative was largely that of Professor Walther Manshard (Freiburg and United Nations universities). The workshop was part of the Resource Policy and Management Programme of the UNU. It is anticipated that it will catalyse the efforts of the University to establish field research projects under the Programme as well as under the existing series of biennial Global View and other workshops. The Oxford meeting impinges on tasks of the Associated Institutions of the UNU and the Research and Training Institutes that are being initiated. The outcome of the Forests, Climate, and Hydrology Workshop should also promote the Fellowship Programme of the UNU as well as their publications programme.

Through their enthusiastic and critical contributions the participants are largely responsible for the success of the workshop. We wish to acknowledge the assistance of the Meteorological Office (Bracknell, UK) and the Institute of Hydrology (Crowmarsh, UK) in planning the workshop and especially Dr. Howard Oliver (Institute of Hydrology) for his help during the meeting.

The bulk of this book comprises the reviews prepared in advance of the workshop for selected areas of the subject. The reviewers kindly accepted many of our suggestions and the changes necessary to achieve a degree of conformity among the various chapters. The authors brought to the notice of the workshop participants the most recent investigations: the bibliographies following each contribution should prove particularly valuable. Interpretations of data were usually critical and carry suggestions of the physical processes involved. Special mention should be made of Dr. David Mabberley's lecture (chap. 2) presented to the members of the workshop and their guests at a reception given at the Commonwealth Forestry Institute, University of Oxford.

This showed the biological significance, complexity, and dynamism of the tropical rain forest as a background to the deliberations of the workshop on the regional and global climatic impact of its exploitation. Only the scale of the hydrological and climatological phenomena treated is implied by our use of "regional": we do not wish to confine our considerations to named geographical regions. However, among the local case studies that were communicated to the workshop, we have taken the opportunity of publishing that by Dr. Meher-Homji. This respresents perhaps the most refined of the challenging genre of somewhat anecdotal evidence for associating changing forest extent with changing rain climate. As with the Russian research (chap. 5), intriguing correlations in hydrology ought to generate quantitative hypotheses as to the underlying physical mechanisms, and these should be critically tested.

A number of experts from various disciplines were invited to the workshop with the reviewers to comment on the evidence and to suggest an appropriate course for future investigations. These assessments, much abbreviated and more the consensus of the workshop rather than merely the contributions of individual participants, are appended to each paper. At two points during the workshop, a resume of the preceding papers was presented. These and the resulting discussions are reported in the first part of chapter 10. Since a major objective of the workshop was to produce from the reviews and subsequent discussions conclusions as far as agreement by the participants could be achieved, the last day of the workshop was devoted to this end. The second part of chapter 10 sets out these conclusions. It was not appropriate to direct these at specific agencies, so they can hardly be termed recommendations or guidelines. However, it is to be hoped that scientists involved in the climatic and hydrologic effects of land use changes will be stimulated by the conclusions of the workshop, that agencies supporting research will refer to this consensus, and that those who determine policies of land use will find them informative.

Oxford University
August 1984

Evan R. C. Reynolds
Frank B. Thompson

Contents - Next