Groundwater and Soil Moisture Conditions from GRACE and GRACE-FO Data Assimilation L4 7-days 0.25 x 0.25 degree Global V3.0 (GRACEDADM_CLSM025GL_7D) at GES DISC

Scientists at NASA Goddard Space Flight Center generate groundwater and soil moisture drought indicators each week. They are based on terrestrial water storage observations derived from GRACE-FO satellite data and integrated with other observations, using a sophisticated numerical model of land surface water and energy processes.

This data product is GRACE Data Assimilation for Drought Monitoring (GRACE-DA-DM) Global Version 3.0 from a global GRACE and GRACE-FO data assimilation and drought indicator product generation (Li et al., 2019). It varies from the other GRACE-DA-DM products which are from the U.S. GRACE-based drought indicator product generation (Houborg et al., 2012).
The GRACE-DA-DM Global V3.0 is similar to the GRACE-DA-DM U.S. V4.0 product. Both products are based on the Catchment Land Surface Model (CLSM) Fortuna 2.5 version simulation that was created within the Land Information System data assimilation framework (Kumar et al., 2016). GRACE-DA-DM Global V3.0 drought indicator maps are derived from the GLDAS_CLSM025_DA1_D product, at 0.25 degree resolution, forced by ECMWF meteorological data, and assimilated RL06 GRACE and GRACE-FO data from the University of Texas at Austin (Save et al., 2016; Save, 2020). The GRACE-DA-DM U.S. V4.0 is at 0.125 degree, which is based on a model simulation (not published at GES DISC) forced by NLDAS-2 meteorological data and assimilated with RL06 GRACE/GRACE-FO data.
More information on GRACE-DA-DM U.S. V4.0 and previous versions of the data can be found in the README.

The GRACE-DA-DM Global V3.0 data product contains three drought indicators: Groundwater Percentile, Root Zone Soil Moisture Percentile, and Surface Soil Moisture Percentile. These drought indicators express wet or dry conditions as a percentile, indicating the probability of occurrence within the period of record from 1948 to 2014. The drought indicator data are daily, but available only one day (Monday) per week. The data have a spatial resolution of 0.25 x 0.25 degree with global coverage (60S, 180W, 90N, 180E), and a temporal range from February 2003 to present (with a 3-6 month latency). The data are archived in NetCDF format.

The GRACE-DA-DM is an operational project which produces groundwater and soil moisture drought indicators each week. The operational data is available weekly with a 2-9 day latency from the NASA GRACE project home page found under the Documentation tab. The GRACE-DA-DM data distributed here at GESDISC is the final archive version, which is generated after the latest GRACE-FO data are available.

NASA戈达德太空飞行中心（NASA Goddard Space Flight Center）的科学家每周生成地下水与土壤湿度干旱指标。该类指标基于GRACE-FO（重力恢复与气候实验后续任务，Gravity Recovery and Climate Experiment Follow-On）卫星反演的陆地水储量观测数据，并结合其他观测资料，通过一套高精度的地表水文与能量过程数值模型整合生成。

本数据产品为GRACE干旱监测数据同化系统（GRACE Data Assimilation for Drought Monitoring, GRACE-DA-DM）全球版3.0，源自全球GRACE与GRACE-FO数据同化及干旱指标生成项目（Li等，2019）。其与基于美国GRACE的干旱指标生成项目（Houborg等，2012）产出的其他GRACE-DA-DM产品存在差异。

GRACE-DA-DM全球版3.0与GRACE-DA-DM美国版4.0产品具有较高相似性，二者均基于陆面信息系统（Land Information System, LIS）数据同化框架下开发的流域陆面模型（Catchment Land Surface Model, CLSM）Fortuna 2.5版本模拟结果（Kumar等，2016）。GRACE-DA-DM全球版3.0的干旱指标地图源自GLDAS_CLSM025_DA1_D产品，空间分辨率为0.25度，以欧洲中期天气预报中心（ECMWF）气象数据为驱动场，并同化了德克萨斯大学奥斯汀分校发布的RL06版本GRACE与GRACE-FO数据（Save等，2016；Save，2020）。GRACE-DA-DM美国版4.0的空间分辨率为0.125度，其基于一套由北美陆面数据同化系统第二版（North American Land Data Assimilation System Version 2, NLDAS-2）气象数据驱动的模型模拟结果（未在GES DISC发布），并同化了RL06版本GRACE/GRACE-FO数据。

有关GRACE-DA-DM美国版4.0及该数据集过往版本的更多信息，请参阅README文件。

GRACE-DA-DM全球版3.0数据产品包含三类干旱指标：地下水百分位数、根区土壤湿度百分位数以及表层土壤湿度百分位数。此类干旱指标以百分位数形式表征地表干湿状况，反映了1948年至2014年记录期内该状况的发生概率。该干旱指标数据为日尺度数据，但仅每周更新一次（更新日为周一）。数据空间分辨率为0.25×0.25度，覆盖全球范围（范围为南纬60°、西经180°、北纬90°、东经180°），时间跨度为2003年2月至今，数据存在3至6个月的发布延迟。数据以NetCDF格式归档存储。

GRACE-DA-DM是一项业务化项目，每周产出地下水与土壤湿度干旱指标。其业务数据可通过NASA GRACE项目主页的“文档”（Documentation）标签页获取，更新周期为每周，数据发布延迟为2至9天。本次在GES DISC分发的GRACE-DA-DM数据为最终存档版本，该版本在最新GRACE-FO数据可用后生成。