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Bush, Sidney A ¹ ; Barnard, Holly R ² ; Ebel, Brian ³ ; Stallard, Robert F ⁴

¹ Institute of Arctic and Alpine Research
² Institute of Arctic and Alpine Research
³ U.S. Geological Survey
⁴ U.S. Geological Survey

Since European development in the tropics, land-use and land-cover have changed dramatically with conversion of forests to subsistence farms and cattle pastures. Human land-use decisions alter vegetation and soil structure that determine hydrologic flow paths and storage, both of which play an important role in the delivery of freshwater to nearby streams. The timing and amount of freshwater delivery is vital to water resource management, particularly for the Panama Canal and its lock system. Previous research in Central Panama, an area exemplary of land-use change in the tropics, suggests complex feedbacks among land-use, subsurface storage and runoff generation [Ogden et al., 2013; Zimmermann et al., 2014]. We investigated the influence of land-use on runoff generation mechanisms between two catchments characterized by distinctly different land-uses within the Panama Canal Watershed: an old secondary forest and an active cattle pasture. We evaluated surface runoff by installing three difference infiltrometer systems [Moody and Ebel, 2014] along the hillslopes of each catchment. We then compared runoff ratios, as well as secondary soil properties and streamflow data, between the forest and pasture sites. Preliminary results from our study indicate that runoff was consistently higher at the pasture site than at the old secondary forest site. However, runoff generation following a rain event is influenced greatly by antecedent soil conditions, rainfall intensity and rainfall duration. In many tropical regions water shortages are already common, and there is a high likelihood of further stress from longer dry seasons and more frequent, high-intensity storms caused by accelerating climate change. Enhancing our understanding of runoff generation in the tropics will be of vital importance in mitigating these challenges.

Moody, J. A. and Ebel, B. A. (2012), Difference infiltrometer: a method to measure temporally variable infiltration rates during rainstorms. Hydrol. Process., 26: 3312–3318. doi:10.1002/hyp.9424

Ogden, F. L., T. D. Crouch, R. F. Stallard, and J. S. Hall (2013), Effect of land cover and use on dry season river runoff, runoff efficiency, and peak storm runoff in the seasonal tropics of Central Panama, Water Resour. Res., 49, doi:10.1002/ 2013WR013956.

Zimmermann, B., A. Zimmermann, B. L. Turner, T. Francke, and H. Elsenbeer (2014), Connectivity of overland flow by drainage network expansion in a rain forest catchment, Water Resour. Res., 50, 1457–1473, doi:10.1002/ 2012WR012660.