A climatic control on river network geometry

Channel networks dissect most of the Earth`s surface, draining the rain falling onto the ground. Yet the understanding how these networks form and how they evolve in time remains unclear. By analyzing over one million digitally mapped rivers in the continental United States, we find that the branching angles of low order junctions strongly correlate with the recharge of the ground water given by the ratio between evapotranspiration and precipitation. Theory predicts that bifurcating channels incised by re-emerging groundwater flow split at a characteristic angle of α=2π/5=72° (Devauchelle et al, 2012). This case clearly emerges as a limiting case for high recharge while in dry areas dominated by surface runoff the branching angle is much lower. Our analysis suggests that, contrary to most current theories, groundwater flow plays an important role in the formation and evolution of channel networks on a continental scale. O. Devauchelle, A. Petroff, H.J. Seybold and D. Rothman; Ramification of stream networks, PNAS (2012) 109 (51) 20775-20776;