Modeling Climate and Tectonic Controls on Bias in Measured River Incision Rates.

Rates of land surface processes provide insights into climatic and tectonic influences on topography. Bedrock incision rates are estimated by dating perched landforms such as strath terraces, assuming a constant bedrock incision rate from terrace abandonment to the next terrace level or present river level. These estimates express biases from the stochastic nature of sediment and water discharge in controlling river incision as well as from using a mobile channel elevation as a reference frame, leading to different incision rates when calculated over different timeframes. We introduce a 1‐D model incorporating fluvial mechanics, tectonics, sediment, and climate variability to predict these biases and assess their sensitivity to climate and tectonics. Findings suggest biases intensify under highly variable climates and slow rock uplift, with climate periodicity being a primary control for our modeled scenarios. Our model provides a mechanism to improve river incision measurement uncertainty, impacting paleoclimate and tectonic geomorphology reconstructions. Plain Language Summary: Geomorphologists often measure how fast rivers erode bedrock over time by dating river terraces that have been uplifted to be higher than the elevation of the modern river channel. This helps us learn how landscapes evolve and about what past climates were like over long timescales. But this method is complicated by the fact that rivers do not erode rocks at a steady rate and the elevation of the channel surface above which we measure terrace height changes over time. We present a numerical model that predicts how these terraces develop under different climates and rates of rock uplift. Model results imply that measurements of long‐term river incision are most susceptible to temporal bias in regions experiencing highly variable paleo‐climate and slow rock uplift. Our model helps us make better measurements of river erosion and understand how climate and rock uplift shape landscapes. Key Points: We present a numerical model that reproduces biases in rates of river incision measured from strath terracesWe find that these measurement biases are the strongest when climates are highly variable and rock uplift is slowUnderstanding bedrock incision measurement biases allows for bias correction in field studies and improves data comparability [ABSTRACT FROM AUTHOR]