GLDAS Change in Storage 2000 - Present

Calculating the total volume of water stored in a landscape can be challenging. In addition to lakes and reservoirs, water can be stored in soil, snowpack, or even inside plants and animals, and tracking the all these different mediums is not generally possible. However, calculating the change in storage is easy - just subtract the water output from the water input. Using the GLDAS layers we can do this calculation for every month from January 2000 to the present day. The precipitation layer tells us the input to each cell and runoff plus evapotranspiration is the output. When the input is higher than the output during a given month, it means water was stored. When output is higher than input, storage is being depleted. Generally the change in storage should be close to the change in soil moisture content plus the change in snowpack, but it will not match up exactly because of the other storage mediums discussed above. Dataset Summary The GLDAS Change in Storage layer is a time-enabled image service that shows net monthly change in storage from 2000 to the present, measured in millimeters of water. 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: Change in Water Storage 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 for Desktop. It is useful for scientific modeling, but only at global scales. In ArcGIS Pro you can use the built-in raster functions or create your own to create custom extracts of the data. Imagery layers provide fast, powerful inputs to geoprocessing tools, models, or Python scripts in Pro. Online you can filter the layer to show subsets of the data using the filter button and the layer's built-in raster functions. By applying the "Calculate Anomaly" raster function, it is possible to view these data in terms of deviation from the mean, instead of total change in storage. Mean change in storage 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 change in storage 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.计算地表储水总量颇具挑战。除湖泊与水库外，水还可储存于土壤、积雪层，甚至动植物体内，但全面追踪这些不同储水介质通常难以实现。不过，计算储水量变化却较为简单——只需将水输出量减去水输入量即可。借助全球陆面数据同化系统（Global Land Data Assimilation System，GLDAS）图层，我们可对2000年1月至今的逐月数据完成该计算。其中，降水图层代表各栅格单元的水输入量，而径流与蒸散发之和则为水输出量。若某一月份输入量高于输出量，则意味着该月储水量有所增加；若输出量高于输入量，则储水量被消耗。通常而言，储水量变化应与土壤含水量变化及积雪层变化之和较为接近，但由于前文提及的其他储水介质的存在，二者无法完全匹配。 数据集摘要 GLDAS储水变化图层是一项启用了时间功能的影像服务，展示了2000年至今的逐月净储水量变化，单位为毫米水深。该数据集由美国国家航空航天局（National Aeronautics and Space Administration，NASA）采用Noah陆面模型计算得到，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2.1版本（Global Land Data Assimilation System-2.1，GLDAS-2.1）的卫星与地面观测数据。模型以3小时为时间步长运行，并聚合为月均数据。可查阅完整的模型输入参数列表，探索GRIB格式的输出数据，亦可访问完整的水文目录以获取所有相关数据与信息！ 映射现象：储水量变化 单位：毫米 时间间隔：逐月 时间范围：2000年1月1日至今 栅格单元尺寸：28千米 数据源类型：科学数据 像素类型：有符号整数 数据投影：GCS WGS84 镶嵌投影：Web Mercator Auxiliary Sphere 覆盖范围：全球陆面 来源：美国国家航空航天局（NASA） 更新周期：不定期 该图层可应用场景： 该图层既可用于可视化展示，也可用于分析研究。它可在ArcGIS Online中应用于网页地图与各类应用，也可在ArcGIS Desktop中使用。该图层适用于全球尺度的科学建模，但仅支持全球尺度的应用。在ArcGIS Pro中，您可使用内置的栅格函数，或自定义函数来提取定制化的数据子集。影像图层可为ArcGIS Pro中的地理处理工具、模型或Python脚本提供高效且强大的输入数据。在在线平台中，您可通过筛选按钮与图层内置的栅格函数，对图层进行过滤以展示数据子集。通过应用"计算距平（Calculate Anomaly）"栅格函数，可将数据以相对于平均值的偏差形式展示，而非直接展示储水量总变化量。指定月份的平均储水量变化量是基于2000年至今的完整记录时段计算得到的。 时间：本图层为启用时间功能的图层。默认情况下，它将显示地图时间范围内的第一个月份。若禁用时间动画功能，则可通过图层的多维设置来设置时间范围。若需计算某一时间范围内的储水量变化的平均值、总和或最值，请更改用于解决重叠像素的镶嵌算子。在ArcGIS Online中，可在"影像显示顺序"选项卡中完成设置；在ArcGIS Pro中，可通过"数据"选项卡进行设置；在ArcMap中，则需在图层属性窗口的"镶嵌"选项卡中操作。最小时间范围为1个月，最大为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，必须在图层属性窗口的处理模板选项卡中，将渲染器从制图渲染器切换为分析渲染器。