资源环境科技发展态势分析平台

Rainfall is an important driver of erosion processes. The mean rainfall rate is often used to account for the erosive impact of a particular climate. However, for some erosion processes, erosion rate is a nonlinear function of rainfall, e.g., due to a threshold for erosion. When this is the case, it is important to take into account the full distribution of rainfall, instead of just the mean. In light of this, we have characterized the variability of daily rainfall over the Himalayan orogen using high spatial and temporal resolution rainfall data sets. We find significant variations in rainfall variability over the Himalayan orogen, with increasing rainfall variability to the west and north of the orogen. By taking into account variability of rainfall in addition to mean rainfall rate, we find a pattern of rainfall that, from a geomorphological perspective, is significantly different from mean rainfall rate alone. Using these findings, we argue that short-term rainfall variability may help explain observed short and long-term erosion rates in the Himalayan orogen.

Plain Language Summary An important topic in earth science is understanding how climate and tectonic forces interact to shape the surface of the Earth. One of the main influences that climate has on the Earth's surface is to cause erosion by delivering water to landscapes as rain and snow. Wetter climates should, in general, cause more erosion than drier climates, which is why the mean annual rainfall has traditionally been used as a measure of the erosive strength of climate. However, field evidence seems to suggest that the effect of climate is more sophisticated than can be captured with the mean annual rainfall. There is a considerable body of theory demonstrating that the intensity of rainfall, or storminess, is an equally important aspect of how climate causes erosion. In light of this, we have characterized the storminess in the Himalayan mountain range, a place with high erosion rates driven by rainfall. We show that there is large variation in storminess from place to place in the Himalayas, and that this can help explain observed rates of erosion, which do not match mean annual rainfall rates.