Arctic lakes located in permafrost regions are susceptible to catastrophic drainage. In this study, we reconstructed historical lake drainage events on the western Arctic Coastal Plain of Alaska between 1955 and 2017 using USGS topographic maps, historical aerial photography (1955), and Landsat Imagery (ca. 1975, ca. 2000, and annually since 2000). We identified 98 lakes larger than 10 ha that partially (>25% of area) or completely drained during the 62‐year period. Decadal‐scale lake drainage rates progressively declined from 2.0 lakes/yr (1955–1975), to 1.6 lakes/yr (1975–2000), and to 1.2 lakes/yr (2000–2017) in the ~30,000‐km2 study area. Detailed Landsat trend analysis between 2000 and 2017 identified two years, 2004 and 2006, with a cluster (five or more) of lake drainages probably associated with bank overtopping or headward erosion. To identify future potential lake drainages, we combined the historical lake drainage observations with a geospatial dataset describing lake elevation, hydrologic connectivity, and adjacent lake margin topographic gradients developed with a 5‐m‐resolution digital surface model. We identified ~1900 lakes likely to be prone to drainage in the future. Of the 20 lakes that drained in the most recent study period, 85% were identified in this future lake drainage potential dataset. Our assessment of historical lake drainage magnitude, mechanisms and pathways, and identification of potential future lake drainages provides insights into how arctic lowland landscapes may change and evolve in the coming decades to centuries.

The Pacific Coast of the Baja California Peninsula (BCP), Mexico, is a hotspot for foraging loggerhead turtles Caretta caretta originating from nesting beaches in Japan. The BCP region is also known for anthropogenic sea turtle mortality that numbers thousands of turtles annually. To put the conservation implications of this mortality into biological context, we conducted aerial surveys to determine the distribution and abundance of loggerhead turtles in the Gulf of Ulloa, along the BCP Pacific Coast. Each year from 2005 to 2007, we surveyed ca. 3700 km of transect lines, including areas up to 140 km offshore. During these surveys, we detected loggerhead turtles at the water's surface on 755 occasions (total of 785 loggerheads in groups of up to 7 turtles). We applied standard line-transect methods to estimate sea turtle abundance for survey data collected during good to excellent sighting conditions, which included 447 loggerhead sightings during 6400 km of survey effort. We derived the proportion of time that loggerheads were at the surface and visible to surveyors based on in situ dive data. The mean annual abundance of 43 226 loggerhead turtles (CV = 0.51, 95% CI range = 15 017 to 100 444) represents the first abundance estimate for foraging North Pacific loggerheads based on robust analytical approaches. Our density estimate confirms the importance of the BCP as a major foraging area for loggerhead turtles in the North Pacific. In the context of annual mortality estimates of loggerheads near BCP, these results suggest that up to 11% of the region's loggerhead population may perish each year due to anthropogenic and/or natural threats. We calculate that up to 50% of the loggerhead turtles residing in the BCP region in any given year will die within 15 yr if current mortality rates continue. This underscores the urgent need to minimize anthropogenic and natural mortality of local loggerheads.

Snowdrift, which results from deposition of wind transported snow, has been primarily estimated empirically rather than using physically-based modelling since the snow redistribution process is extremely complex. This study demonstrates a practical predictive model for snow redistribution based on the Linear Particle Distribution equation, which consists of snow surface diffusion, snow surface advection, and snow surface erosion components. Here, we focus on numerical model development and implementation for two-dimensional natural terrains at meter-scale resolutions with and without perforated snow fences, which has been difficult to model in a twodimensional field. First, a selected numerical scheme was implemented in the Snow Movement Over Open Terrain for Hydrology model platform and tested by the exact solutions under a few well-defined boundary conditions. Then, to simulate snowdrifts around the snow detention structures in the middle of the computational domain, an equivalent solid snow fence concept was introduced and tested. The model was applied to several terrains in the Laramie Range, Wyoming, and at two sites on the North Slope of Alaska, where wind-induced snow redistribution plays a major role.Data from Airborne Light Detection and Ranging, Ground Penetrating Radar, and Unmanned Aerial Vehicle photogrammetry were used to calibrate and validate the model. The numerical snow redistribution model effectively reproduces the observed snowdrift distributions when snow densification and snowmelt effects were minimal.The model applications illustrated that the diffusion effect generally dominated snow redistribution with limited contributions of advection and erosion effects for abrupt terrain transition and perforated object, respectively.

Lakes and drained lake basins (DLBs) combined are estimated to cover up to ∼80% of the western Arctic Coastal Plain of Alaska (∼30,000 km 2) (Grosse et al., 2013; Hinkel et al., 2005; Jones & Arp, 2015). There are a variety of lake types in the Arctic, but the most common are thermokarst lakes in lowland regions with ice-rich permafrost (Grosse et al., 2013; Kling, 2009) that form due to permafrost thaw and surface subsidence. Deeper lakes developed in permafrost terrain are often underlain by layers or bodies of perennially unfrozen ground below the lake bed known as a talik (van Everdingen, 1998). Arctic lakes can persist for thousands of years, but, due to ongoing margin expansion and other landscape changes, they eventually drain laterally to create a mosaic of extant lakes and DLBs (Hinkel et al. 2007; Mackay, 1992). Arctic lake drainage can occur through a variety of processes, and where and when lake drainage occurs influences landscape succession and permafrost aggradation (refreezing of the talik). Remote-sensing analysis of historical imagery of the western Arctic Coastal Plain of Alaska identified that 1-2 lakes larger than 10 ha have partially (>25% area reduction) or completely drained per year between

The presence and thickness of snow overlying lake ice affects both the timing of melt and ice-free conditions, can contribute to overall ice thickness through its insulative capacity, and fosters the development of variable ice types. The use of UAVs to retrieve snow depths with high spatial resolution is necessary for the next generation of ultra-fine hydrological models, as the direct contribution of water from snow on lake ice is unknown. Such information is critical to the understanding of the physical processes of snow redistribution and capture in catchments on small lakes in the Arctic, which has been historically estimated from its relationship to terrestrial snowpack properties. In this study, we use a quad-copter UAV and SfM principles to retrieve and map snow depth at the winter maximum at high resolution over a the freshwater West Twin Lake on the Arctic Coastal Plain of northern Alaska. The accuracy of the snow depth retrievals is assessed using in-situ observations (n = 1,044), applying corrections to account for the freeboard of floating ice. The average snow depth from in-situ observations was used calculate a correction factor based on the freeboard of the ice to retrieve snow depth from UAV acquisitions (RMSE = 0.06 and 0.07 m for two transects on the lake. The retrieved snow depth map exhibits drift structures that have height deviations with a root mean square (RMS) of 0.08 m (correlation length = 13.8 m) for a transect on the west side of the lake, and an RMS of 0.07 m (correlation length = 18.7 m) on the east. Snow drifts present on the lake also correspond to previous investigations regarding the variability of snow on lakes, with a periodicity (separation) of 20 and 16 m for the west and east side of the lake, respectively. This study represents the first retrieval of snow depth on a frozen lake surface from a UAV using photogrammetry, and promotes the potential for high-resolution snow depth retrieval on small ponds and lakes that comprise a significant portion of landcover in Arctic environments.