“Light the Flow with Sense and Color”: Exploring Mountain Hydrology with RGB and Thermal Imagery

Abstract:

Water in the Western United States primarily originates from sub-alpine, snow dominated systems. Despite the importance, the processes translating snowpack to streamflow remain difficult to understand. Spatial variability of precipitation, topography and vegetation contribute to the elusiveness of runoff generation processes in mountainous watersheds by affecting snow deposition and melt. Much of the uncertainty in understanding how a snowpack becomes stream flow is due to spatial or temporal incoherence in observations; whether using point data or satellite imagery, important measurements are often missed or assumed. Despite the challenges of ascertaining the connection of snowmelt and watershed runoff generation at every scale, with this study, we aim to bridge an observational gap with new methods offering insights that were previously difficult to measure and quantify. Over a two-year period, we employed both remote sensing technologies and in-situ observations to better discern runoff generation in a small sub-alpine watershed in the Snowy Range of Southeast Wyoming. We used an unmanned aerial vehicle (UAV) equipped with a combined high-resolution RGB and thermal camera to measure the spatial evolution of snowpack and saturated areas during the snowmelt and summer dry down period. This combined imagery allows for delineation of both snowpack extent and depth and contributing saturated areas. The imagery is coupled with two years of on-the-ground snow depth measurements, soil moisture, meteorological, and streamflow data. The annual spatial variability of snowmelt and saturated areas offers further process insights which may clarify the local connectivity of this watershed and offer indications of where groundwater and surface water interaction occurs as well as the spatiotemporal evolution of runoff generation. Our research explores the viability of UAV-based thermal mapping of runoff source areas at the small watershed scale; offering a link in spatial scales in hydrologic research, providing a more comprehensive picture of runoff source areas and snowmelt dynamics in small mountainous watersheds.