Tropical forests and water in a changing world: Adding soil degradation to the equation for more realism

Abstract

This presentation summarizes the state of play with regard to the streamflow impacts of converting tropical forests to other land uses and vice versa (i.e., reforestation and regreening), focusing in particular on the associated changes in annual and seasonal streamflow totals (‘water yield’), peak flows (‘floods’), and emphasizing rainfall infiltration into the soil as a key process. In doing so, both traditional ‘laymen’ views and modern ‘scientific’ paradigms are scrutinized and compared with the best available observational evidence for ‘real-world’ situations as opposed to controlled catchment experiments only.

The widely accepted scientific view that most of the increase in annual streamflow totals after (experimental) forest removal occurs in the form of enhanced baseflows (dry season flows), is increasingly contradicted by real-world observations. Advanced soil degradation due to mismanagement of post-forest land is often reported to lead to diminished dry season flows due to a gradual loss of the former high infiltration capacity of the forest soil.

On a related note, the rainfall-enhancing effect of forest has received renewed attention of late with the advent of moisture-tracking models predicting where the water evaporated by regional-scale forests may be returned again in the form of precipitation. The topic remains highly contentious, however, with model-predicted effects of forest evaporation on rainfall received in specific downwind areas as yet being at odds with evidence provided by stable isotope applications as to the source of the moisture (oceanic vs. terrestrial evaporation).

About the speaker

Dr. L.A. (Sampurno) Bruijnzeel, is a professor of Land Use and Hydrology at the Faculty of Earth and Life Sciences, VU University Amsterdam. He has nearly 40 years of experience of hydrological research in the humid tropics of South- and South-East Asia, the Pacific, the Caribbean, and Central and South America.

He has co-authored some 220 scientific publications and has a 35 years of teaching experience in hydrology. He has been a recipient of the Busk Medal of the Royal Geographical Society (UK) for Biosphere research in the humid tropics (June 2005).