Northwestern Arctic Alaska surface water area vector files, Kotzebue study area, 2002-2019

Arctic landscapes are in a state of transition due to changes in climate occurring during both the summer and winter seasons. Scattered observations indicate that beavers (Castor canadensis) have moved from the forest into tundra areas during the last 20 years, likely in response to broader physical and ecosystem changes occurring in Arctic and Boreal regions. The implications of beaver inhabitation in the Arctic and Boreal are unique relative to other ecosystems due to the presence of permafrost and its vulnerability associated with beaver dams and inundation. Our study specifically examines the role of beavers in controlling surface water dynamics and related thermokarst development in low Arctic tundra regions. We mapped the number of beaver dams visible in sub-meter resolution satellite images acquired between 2002 and 2019 for a 100 square kilometer study area (12 years of imagery) near Kotzebue, Alaska and a 430 square kilometer study area (3 years of imagery) encompassing the entire northern Baldwin Peninsula, Alaska. We show that during the last two decades beaver-driven ecosystem engineering is responsible for the majority of surface water area changes and inferred thermokarst development in the study area. This has implications for interpreting surface water area changes and thermokarst dynamics in other Arctic and Boreal regions that may also result from beaver dam building activities. This geospatial dataset provides polygon vector files representing surface water area in a 100 square kilometer study area located near Kotzebue, Alaska. Surface water area maps were created using sub-meter resolution satellite imagery for the years 2002, 2007-2014, and 2017-2019. Image selection focused on cloud-free, ice-free, and calm surface water conditions with images being acquired between late-June and mid-August in a given year. All images were resampled to a spatial resolution of 70 centimeter to match the lowest resolution image in the time series prior to analysis. Within year image dates range from 25 June to 22 August with the average date of image acquisition being 17 July (table 1). Object-based image analysis was conducted in eCognition Essentials 1.3.

北极景观因夏冬两季的气候变化正处于转型阶段。现有分散观测结果表明，近20年来，北美河狸（Castor canadensis）已从森林区域迁徙至苔原地带，这一现象大概率是对北极与北方针叶林区域更广泛的物理环境及生态系统变化的响应。相较于其他生态系统，河狸在北极及北方针叶林区域栖息所带来的影响具有特殊性，这源于永久冻土（permafrost）的存在，以及河狸坝与积水作用对永久冻土造成的脆弱性。本研究专门探讨了河狸在调控北极低地苔原区域的地表水动态及相关热喀斯特（thermokarst）发育过程中的作用。我们对两处研究区域内2002年至2019年间获取的亚米级分辨率（sub-meter resolution）卫星影像中的可见河狸坝数量进行了测绘：一处是阿拉斯加科策布附近的100平方千米研究区（对应12年的影像数据），另一处是涵盖阿拉斯加北部鲍德温半岛全境的430平方千米研究区（对应3年的影像数据）。研究结果显示，近二十年来，由河狸主导的生态系统工程活动是研究区域内地表水面积变化及推断出的热喀斯特发育的主要驱动因素。这一发现对于解读其他北极及北方针叶林区域的地表水面积变化与热喀斯特动态具有重要参考价值——这些区域的同类变化同样可能由河狸筑坝活动引发。本地理空间数据集提供了阿拉斯加科策布附近100平方千米研究区内的地表水面积多边形矢量文件（vector files）。地表水面积图基于2002年、2007-2014年及2017-2019年的亚米级分辨率卫星影像制作而成。影像筛选标准为无云、无冰且水面平静，采集时间集中在每年6月下旬至8月中旬。所有影像均被重采样至70厘米的空间分辨率，以匹配时间序列中分辨率最低的影像，再开展后续分析。年内影像的采集日期范围为6月25日至8月22日，平均采集日期为7月17日（详见表1）。本研究采用eCognition Essentials 1.3软件完成面向对象的影像分析。