Abstract
Seasonal and ephemeral surface water resources are essential to human consumptive uses and the nourishment of aquatic habitats, but they are increasingly threatened by climate-change related impacts. Western North America, for example, has already experienced significant declines in seasonal snow cover, which will have a range of effects on both human communities and aquatic ecosystems like wetlands. The swift rate of change requires consistent monitoring at scales that support adaptive management, but seasonal-ephemeral water resources are often distributed across vast areas that are poorly instrumented. As such, remote sensing is increasingly employed to monitor freshwater resources and understand hydrological processes. This dissertation investigates the application of novel remote sensing approaches to important questions involving the monitoring of seasonal snow supplies and snow-dependent, ephemeral wetlands. Also included is a study examining the socio-ecological context for climate change research and adaptation in the headwaters regions of a large watershed. The first research chapter explores the potential of using terrestrial laser scanning (TLS) for the estimation of intercepted snow masses on trees. The findings indicate good agreement (R2 = 0.69, RMSE = 0.91 kg) between TLS estimates of snow mass and measurements made on trees suspended from load cells. With further refinement, this approach may prove to be a useful tool in calibrating snow interception models to different forest types. The second research chapter utilizes this new technique to fit a Random Forest model that predicts snow interception volume from a suite of canopy metrics derived from aerial laser scanning (ALS). The findings demonstrate good agreement (R2 = 0.65, RMSE = 0.52 m3) between observations and model predictions and identified the best suite of predictors. This suggests that metrics capturing the intrinsic, three-dimensional variability of tree canopies may be useful as new parameters in hydrological or snow interception models. The third research chapter analyzes a thirty-year time series of satellite imagery to identify trends in ephemeral wetland (playa) inundation, with the goal of informing land management practices and wetland restoration planning. The findings indicate that localized weather conditions and hydrologic modification history are important drivers of playa inundation, that reductions in habitat availability and inundation duration should be expected with intensifying droughts, and that a small number of playa have the potential to function as hydrologic refugia during drought years. The fourth research chapter analyzed the spatial and topical distribution of climate change research in the headwaters of the Columbia River Basin. The findings identify broad patterns in a large body of research, such as gaps in interdisciplinary and geographic collaboration, and suggest future directions for understanding climate change across the region. All told, this set of studies adds to the body of knowledge on remote sensing for seasonal-ephemeral water resources, as well as applications for water resources research and management.