Climate, Tectonics, and Topography

When considering potential for climate-tectonic coupling, the climatic component is often estimated with mean precipitation or rainfall. This common simplification ignores both the details of how rainfall is transformed into runoff but also the results of prior work highlighting the importance of daily runoff variability in controlling the sensitivity of topography to changes in tectonics, and thus the extent to which surface processes - tectonic feedbacks are expected. Work in the Greater Caucasus has highlighted the critical importance of the runoff variability and its controls, specifically snowmelt, in explaining topography - erosion rate relationships (Forte et al., 2016, Forte et al., 2022).

Normalized channel steepness (ksn) is a common and useful topographic metric that has been demonstrated to be related to rates of rock uplift rate. Importantly though, calculation of ksn embeds a variety of very simple assumptions, like spatially constant precipitation and resulting runoff. A promising alternative is a discharge weighted form of the normalized channel steepness, i.e., ksnQ. In regions with large gradients in precipitation, using ksnQ to relate to erosion rates allows for more accurate and flexible estimates of rock uplift rates and how topography may or may not reflect lithologic variations (Adams et al., 2020). This analysis has now been extended to include the entire frontal Himalaya (Whipple et al., 2023)

Prior work, from myself and others, has indicated that when considering how topography reflects interactions between climatically mediated surface processes and tectonics, it is critical to consider both (1) the interaction of daily runoff variability with thresholds to erosion and (2) orographic gradients in precipitation and runoff. However, limited work has considered these two processes together. Preliminary work in combining these two concepts suggests that orographic gradients in runoff variability are expected and this generally predicts strongly non-linear erosion rate - topography relationships (Forte & Rossi, 2024a, Forte & Rossi, 2024b).