GLDAS Snowpack 2000 - Present

Melting snowpack is a key part of the spring water budget in many parts of the world. Like a natural reservoir, snowpack stores winter precipitation and releases it as runoff over the course of many months. Where summer rains are scarce snowpack provides crucial base flow without which rivers might go dry. Where summer rains are torrential, this exacerbates the flooding and can lead to the loss of lives. This map contains a historical record showing the water stored in snowpack during each month from March 2000 to the present. It is not a map of snow depth, but of snow water equivalent, which is the amount of water that would be produced if all the snow melted. For fresh snow, this can be anywhere from 5% to 20% the depth of the snow, depending on temperature (snow tends to be fluffier at lower temperatures). As the snow settles and melts, it becomes more dense, up to 40% or 50% in the spring. Temperature, albedo (the reflective property of the snow), density, and volume all affect the melting rate of the snowpack. Additionally, melting rate is influenced by wind, relative humidity, air temperature and solar radiation. Dataset Summary The GLDAS Snowpack layer is a time-enabled image service that shows average monthly snowpack from 2000 to present, measured in millimeters of snow water equivalent. It is calculated by NASA using the Noah land surface model, run at 0.25 degree spatial resolution using satellite and ground-based observational data from the Global Land Data Assimilation System (GLDAS-2.1). The model is run with 3-hourly time steps and aggregated into monthly averages. Review the complete list of model inputs, explore the output data (in GRIB format), and see the full Hydrology Catalog for all related data and information! Phenomenon Mapped: Snowpack Units: Millimeters Time Interval: Monthly Time Extent: 2000/01/01 to present Cell Size: 28 km Source Type: Scientific Pixel Type: Signed Integer Data Projection: GCS WGS84 Mosaic Projection: Web Mercator Auxiliary Sphere Extent: Global Land Surface Source: NASA Update Cycle: Sporadic What can you do with this layer? This layer is suitable for both visualization and analysis. It can be used in ArcGIS Online in web maps and applications and can be used in ArcGIS Desktop. Is useful for scientific modeling, but only at global scales. The GLDAS snowpack data is useful for modeling, but only at global scales. By applying the "Calculate Anomaly" processing template, it is also possible to view these data in terms of deviation from the mean, instead of total snowpack. Mean snowpack for a given month is calculated over the entire period of record - 2000 to present. Time: This is a time-enabled layer. By default, it will show the first month from the map's time extent. Or, if time animation is disabled, a time range can be set using the layer's multidimensional settings. If you wish to calculate the average, sum, or min/max over the time extent, change the mosaic operator used to resolve overlapping pixels. In ArcGIS Online, you do this in the "Image Display Order" tab. In ArcGIS Pro, use the "Data" ribbon. In ArcMap, it is in the 'Mosaic' tab of the layer properties window. The minimum time extent is one month, and the maximum is 8 years. Important: You must switch from the cartographic renderer to the analytic renderer in the processing template tab in the layer properties window before using this layer as an input to geoprocessing tools.积雪融水是全球诸多地区春季水文收支的关键组成部分。如同天然水库一般，积雪（snowpack）会储存冬季降水，并在数月间以径流形式逐步释放。在夏季降雨匮乏的区域，积雪融水提供了至关重要的基流，若无此补给，河流或将彻底干涸；而在夏季暴雨频发的区域，积雪融水则会加剧洪涝灾害，进而危及生命安全。 本数据集附带一份历史记录，展示了2000年3月至今各月份的积雪储水量。该地图并非呈现积雪深度，而是积雪水当量（snow water equivalent）——即所有积雪完全融化后可产出的液态水量。对于新降积雪而言，其积雪水当量约为积雪深度的5%至20%，具体比例取决于气温：气温越低，积雪越疏松蓬松。随着积雪压实与融化，其密度会逐渐升高，春季时可达40%至50%。气温、反照率（albedo，即积雪的反射特性）、密度与体积，均会影响积雪的融化速率。此外，风速、相对湿度、气温与太阳辐射也会对融化速率产生影响。 数据集摘要 GLDAS积雪图层是一项启用了时间维度的影像服务，展示了2000年至今的月均积雪储水量，单位为毫米积雪水当量。该数据集由美国国家航空航天局（NASA）借助Noah陆面模型计算生成，空间分辨率为0.25度，所用数据来自全球陆面数据同化系统（GLDAS-2.1）的卫星与地面观测资料。模型以3小时间隔运行，并聚合为月均数据。 如需查看完整的模型输入参数列表、探索GRIB格式的输出数据，或查阅完整的水文目录获取所有相关数据与信息！ 制图现象：积雪储水 单位：毫米 时间间隔：月度 时间范围：2000年1月1日至今 像元尺寸：28千米 数据来源类型：科学数据集 像元类型：有符号整数 数据投影：GCS WGS84 镶嵌投影：Web Mercator（辅助球面） 覆盖范围：全球陆地区域 数据来源：美国国家航空航天局（NASA） 更新周期：不定期 该图层兼具可视化与分析双重用途，可在ArcGIS Online中用于网页地图与应用程序开发，也可适配ArcGIS Desktop软件。其适用于全球尺度的科学建模：通过应用“计算距平”处理模板，还可将数据转换为相对于多年平均值的偏差值，而非直接展示总积雪储水量。指定月份的多年平均积雪储水量以2000年至今的完整观测记录为基准计算得出。 时间维度：本图层启用了时间维度功能，默认将显示地图时间范围内的首个月份；若关闭时间动画功能，则可通过图层的多维设置自定义时间范围。如需计算指定时间范围内的平均值、总和或极值，可更改用于处理重叠像元的镶嵌算子：在ArcGIS Online中，可在“影像显示顺序”标签页中完成设置；在ArcGIS Pro中，需通过“数据”功能区操作；在ArcMap中，则需在图层属性窗口的“镶嵌”标签页中调整。时间范围的最小跨度为1个月，最大跨度为8年。 重要提示：在将该图层作为地理处理工具的输入数据之前，必须先在图层属性窗口的“处理模板”标签页中，将制图渲染器切换为分析渲染器。