Hydrological and geochemical studies in the seasonal tropics of Panama over the past six years have revealed runoff behaviors not seen in temperate climates. This integrated international research program combines hydrological, geochemical, and geophysical measurements in the seasonal tropics including in situ data collection and analysis, enhanced by the use of natural and introduced tracers and modeling. The overall objective of this collaborative research program is to understand important runoff generating processes in the seasonal tropics and the roles of seasonal transitions and land-use changes on runoff mechanism thresholds. Hydrologic, geochemical and isotopic data collected over a range of scales will compare the virtually pristine 414 km2 old-growth Upper Rio Chagres and adjacent 330 km2 largely deforested Rio Pacora watersheds to examine land-use change effects. Different bedrock types underlay these basins, so geochemistry and isotopes will be used to assist in identifying flow paths and residence times and in model and hypothesis testing. The humid tropics cover 22% of the Earth's land surface and are home to 36% of humanity. The selected study area is representative of the humid tropics promoting transferability of the knowledge gained to a geographically large region. There are three very important questions that this research will help answer. What is the effect of deforestation or reforestation on the water yields from watersheds in the seasonal tropics? Why does runoff generation behave differently early in the rainy season than at other times of the year? How can we better predict these effects by improved hydrologic models? The Panama Canal watershed is extremely important for world commerce because the runoff from the watershed drives the Panama Canal, which is vitally important to the United States. These research results will be communicated to the Panama Canal Authority, Panamanian Universities, and broadly disseminated through peer-review articles. An international field course on tropical hydrology will be held each year of the project and will be open to qualified U.S. and Panamanian graduate and undergraduate students. The project compliments the Smithsonian Tropical Research Institute (STRI) Panama Canal Watershed Experiment, and STRI is a collaborator, as are the Panama Canal Authority and the Technological University of Panama.
