GLDAS Evapotranspiration 2000 - Present

Most of us understand the hydrologic cycle in terms of the visible paths that water can take such as rainstorms, rivers, waterfalls and lakes. However, an even larger volume of water flows through the air all around us in two invisible paths: evaporation and transpiration. These two paths together are referred to as evapotranpsiration (ET), and claim 61% of all terrestrial precipitation. Solar radiation, air temperature, wind speed, soil moisture, and land cover all affect the rate of evapotranspiration, which is a major driver of the global water cycle, and key component of most catchments' water budget. This map contains a historical record showing the volume of water lost to evapotranspiration globally during each month from March 2000 to the present. Dataset Summary The GLDAS Evapotranspiration layer is a time-enabled image service that shows total actual evapotranspiration monthly from 2000 to the present, measured in millimeters of water loss. 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: Evapotranspiration 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. By applying the "Calculate Anomaly" processing template, it is also possible to view these data in terms of deviation from the mean. Mean evapotranspiration 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.多数人对水文循环（hydrologic cycle）的认知，多基于暴雨、河流、瀑布与湖泊这类可见的水文路径。然而，另有体量更为庞大的水体以两种无形路径在我们周遭的大气中运移：蒸发（evaporation）与蒸腾（transpiration）。二者合称蒸散发（evapotranspiration，ET），其耗水量占全球陆地降水总量的61%。太阳辐射、气温、风速、土壤湿度与土地覆被，均会对蒸散发速率产生影响；而蒸散发作为全球水循环的核心驱动因子之一，亦是多数集水区水文预算的关键组成部分。本数据集包含一段历史记录，展示了2000年3月至今全球每月因蒸散发损耗的水体体量。 数据集概述 GLDAS蒸散发图层是一项支持时间维度的影像服务，展示了2000年至今的逐月实际总蒸散发量，单位为毫米水体损耗量。该数据集由美国国家航空航天局（National Aeronautics and Space Administration，NASA）基于Noah陆面模型计算得到，空间分辨率为0.25度，所用数据源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。您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！ 映射参数 映射现象：蒸散发 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 数据源类型：科学数据 像元类型：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：全球陆面 数据来源：NASA 更新周期：不定期 该图层应用场景 本图层可同时适用于可视化与分析工作：可在ArcGIS Online中嵌入网页地图与应用程序，亦可用于ArcGIS Desktop软件。其适用于全球尺度的科学建模工作。通过应用"Calculate Anomaly"处理模板，还可基于与多年均值的偏差对数据进行可视化展示。给定月份的多年平均蒸散发量，是基于2000年至今的全部记录时段计算得到的。 时间维度说明 本图层支持时间维度设置。默认情况下，它将显示地图时间范围内的首个月份；若禁用时间动画功能，则可通过图层的多维设置自定义时间范围。若需计算时间范围内的平均值、总和或最值，请更改用于解决像元重叠问题的镶嵌运算符。在ArcGIS Online中，您可在"Image Display Order"标签页中完成该设置；在ArcGIS Pro中，可通过"Data"功能区操作；在ArcMap中，则需在图层属性窗口的"Mosaic"标签页中完成配置。时间范围的最小跨度为1个月，最大跨度为8年。 重要提示 在将该图层用作地理处理工具的输入数据之前，您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。