**3.1. Map of local relief**

The map of local relief in the present study is produced from River-Tool by subtracting arithmetically a sub-envelope surface that describes the general pattern of valley bottoms elevations from an envelope surface (that connects peaks elevations) [28]. We obtained such surfaces by smoothing the minimum and maximum topography of the SRTM DEM by a 20 km wide circular moving window (**Figure 1C**). We chose the value of 20 km since it is the average spacing of the main valleys (5th, 6th and 7th Strahler order with respect to a critical area of ~4 km2 ). This allowed us to remove small valleys, in effect operating like a low-pass filter that highlights the regional-scale features.
