GLDAS Runoff 2000 - Present

When precipitation falls on the surface of the Earth, much of it is captured in storage (e.g. lakes, aquifers, soil moisture, snowpack, and vegetation). Precipitation that exceeds the storage capacity of the landscape becomes runoff, which flows into river systems. Overland flow is the most visible form of runoff, causing erosion and flash floods, but subsurface flow is the larger contributor in many watersheds. Subsurface flow can emerge on the surface through springs, or more commonly, seep into rivers and lakes through their banks. In urban areas, impervious land cover drastically increases the amount of surface runoff generated, which sweeps trash and urban debris into waterways and increases the likelihood and severity of flash floods. In agricultural areas, surface or subsurface runoff can carry excess salts and nutrients, especially nitrogen and phosphorus. This map contains a historical record showing the amount of runoff generated each month from March 200 to present. It is reported in millimeters, so multiply by a surface area to calculate the total volume of runoff. Dataset Summary The GLDAS Runoff layer is a time-enabled image service that shows average monthly runoff from 2000 to the present measured in millimeters. 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: Runoff 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. t is useful for scientific 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. Mean runoff 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. If you do this, make sure to also select a specific variable. The minimum time extent is one month, and the maximum is 8 years. Variables: This layer has three variables: total runoff, surface flow and subsurface flow. By default total is shown, but you can select a different variable using the multidimensional filter, or by applying the relevant raster function. 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.当降水落至地球表面时，大部分会被储存起来（例如湖泊、含水层、土壤水、积雪以及植被截留）。超过地表储水能力的降水则形成径流，汇入河网系统。地表漫流是最直观的径流形式，会引发侵蚀和山洪，但在许多流域中，地下径流才是径流的主要组成部分。地下径流可通过泉水出露地表，或是更常见地通过河岸渗入江河湖泊。在城市区域，不透水地表覆盖会大幅增加地表径流量，裹挟垃圾与城市废弃物进入水体，并提升山洪发生的概率与灾害强度。在农业区域，地表或地下径流会携带过量盐分与营养物质，尤其是氮和磷。 本数据集包含2000年3月至今的逐月径流量历史记录，单位为毫米，可通过乘以表面积计算径流总体积。 数据集摘要 GLDAS径流图层是一项支持时间维度的影像服务，展示了2000年至今的逐月平均径流量，单位为毫米。该数据集由美国国家航空航天局（NASA）基于Noah陆面模型（Noah Land Surface Model）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（Global Land Data Assimilation System，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。可查阅完整的模型输入参数列表、探索GRIB格式的输出数据，或访问完整的水文目录以获取所有相关数据与信息！ 制图要素 映射现象：径流 单位：毫米 时间间隔：逐月 时间范围：2000年1月1日至今 像元尺寸：28千米 源数据类型：科学数据 像素类型：有符号整数 数据投影：GCS WGS84 镶嵌投影：Web墨卡托辅助球体投影 覆盖范围：全球陆地表层 数据来源：美国国家航空航天局（NASA） 更新周期：不定期 图层用途 本图层适用于可视化与分析工作，可在ArcGIS Online中用于Web地图与应用程序，也可在ArcGIS Desktop中使用。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，还可基于距平值（即与多年平均值的偏差）展示数据。指定月份的多年平均径流量基于2000年至今的完整记录期计算得出。 时间相关说明 本图层支持时间维度。默认情况下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，可通过图层的多维设置指定时间范围。若需计算时间范围内的平均值、总和或极值，请更改用于解决像元重叠问题的镶嵌算子。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"功能区操作；在ArcMap中，则需在图层属性窗口的"镶嵌"选项卡中设置。执行此操作时，请务必同时选择特定的变量。时间范围的最小跨度为1个月，最大跨度为8年。 变量说明 本图层包含三个变量：总径流、地表径流与地下径流。默认显示总径流量，可通过多维过滤器或应用相关栅格函数选择其他变量。 重要提示 在将本图层作为输入用于地理处理工具之前，必须在图层属性窗口的处理模板选项卡中，将制图渲染器切换为分析渲染器。