Orographic barriers, high-resolution TRMM rainfall, and relief variations along the eastern Andes

Quantifying the degree to which tectonic and erosive processes shape landscapes is key to understanding the evolution of tectonically active mountain belts. Here we explore the interplay of these two processes along the humid, eastern flank of the South American Andes. We use high-resolution Tropical Rainfall Measurement Mission (TRMM) and SRTM data to characterize elevation, relief, and hillslope angle of peak rainfall at orographic barriers. Over a distance of more than 3500 km along the eastern flanks, we find that peak rainfall (> 3.5 m/yr) occurs at a mean elevation of 1.3 +/- 0.17 km, a mean relief of 0.95 +/- 0.08 km, and at moderate mean hillslope angles of 18.3 +/- 1.7 degrees. We suggest that topographic relief is the best first-order rainfall predictor and we demonstrate how relief changes along strike south of the Andean orocline alter rainfall distribution. Changes in climatic, sedimentary, and tectonic processes prevent the formation of high relief amounts at the mountain front and these areas are not characterized by pronounced rainfall peak.