Spatiotemporal Variability of Orographic Enhancement in the Sierra Nevada (USA): Results from a Multi-decadal Snow Water Equivalent Reanalysis

Abstract:

An accurate assessment of high-elevation gradients in precipitation across snow-dominated mountainous regions remains a missing piece in the hydrologic and cryospheric sciences. Developing a better understanding of the spatiotemporal variability and distribution of snow water equivalent (SWE) across a mountain chain has significant societal implications particularly related to water resources and flooding. While orographic precipitation is known to be an important process in mountainous terrain, traditional methods for studying orography (e.g. using sparse in situ measurements over a historical record or distributed observations at a few snapshots in time) generally inhibit a full characterization of orographic processes in complex montane regions such as Sierra Nevada, California. A novel high-resolution spatially-distributed SWE reanalysis dataset is used here to characterize the spatial and temporal variability of SWE accumulation across the Sierra Nevada during water years 1985 to present. Orographic gradients in accumulated SWE are diagnosed at multiple temporal scales. A comparison of orographic processes, gradients, SWE volumes, and SWE accumulation rates is presented for windward versus leeward slopes and northern versus southern basins in the Sierra Nevada. The relationships between orographic enhancement and factors such as the underlying physiography and synoptic atmospheric conditions are investigated to explain variability in the seasonal and inter-annual SWE accumulation across the Sierra Nevada.