Global 1-km cropland water-use efficiency from 2001 to 2020 (GCWUE-1km_2001-2020)

The cropland water-use efficiency (WUE) is critical to human well-being and sustainable development goals, among other things. With limited water resources and increasing water demand, improving cropland WUE to reduce water consumption per unit of productivity is a critical way to mitigate global water scarcity. WUE characterizes the trade-off between photosynthetic carbon assimilation and water use, and reflects the capacity of cropland to provide ecosystem services.
The cropland water-use efficiency (WUE) defined in this product refers to the ratio between Net Primary Productivity (NPP) and Evapotranspiration (ET) of croplands (unit: g C⋅kg-1 H2O⋅yr-1). The cropland ET was derived from the “Global daily 1-km actual evapotranspiration from 2000 to 2021” dataset generated by the ETMonitor model using multi-source remote sensing data. Cropland NPP is equal to the Gross Primary Productivity (GPP) minus the fraction of the stored organic carbon consumed by crops to maintain crop respiration (CR). GPP was estimated using an improved Light Use Efficiency model (EF-LUE), accounting for the soil water stress. CR was obtained by summing the growth respiration (proportional to NPP) and maintenance respiration (related to Leaf Area Index, etc.).
Input data for the NPP estimation include (1) the Fraction of Photosynthetically Active Radiation (fPAR) and Leaf Area Index data from the Global LAnd Surface Satellite (GLASS) product, and (2) the downward shortwave radiation, air temperature and dew-point temperature provided by the ERA5 global reanalysis dataset. The global distribution of cropland (including pure cropland pixels and cropland/natural vegetation mosaic pixels) was obtained from the European Space Agency Climate Change Initiative (ESA-CCI) land cover/use classification data.
This product uses the WGS84 coordinate system with latitude and longitude projection (EPSG: 4326). Data are stored in GeoTIFF format. Each file contains one data layer (band) of annual cropland water-use efficiency over croplands of the globe.

农田水分利用效率（cropland water-use efficiency, WUE）对人类福祉与可持续发展目标等诸多方面均至关重要。在水资源总量有限、用水需求持续攀升的背景下，提升农田WUE以降低单位生产力对应的水资源消耗，是缓解全球水资源短缺的关键路径。WUE表征了光合碳同化与水分消耗之间的权衡关系，同时反映了农田提供生态系统服务的能力。
本产品定义的农田水分利用效率（WUE），指农田净初级生产力（Net Primary Productivity, NPP）与农田实际蒸散量（Evapotranspiration, ET）的比值，单位为g C·kg⁻¹ H₂O·yr⁻¹。其中农田ET源自2000—2021年全球逐日1公里分辨率实际蒸散量（Global daily 1-km actual evapotranspiration from 2000 to 2021）数据集，该数据集由ETMonitor模型基于多源遥感数据生成。农田NPP等于总初级生产力（Gross Primary Productivity, GPP）减去作物维持呼吸（crop respiration, CR）所消耗的储存有机碳份额。GPP通过改进型光能利用率模型（EF-LUE）估算，该模型纳入了土壤水分胁迫的影响。CR由生长呼吸（与NPP呈比例关系）与维持呼吸（与叶面积指数等相关）两部分求和得到。
NPP估算所需的输入数据包括：（1）来自全球陆地表面卫星（Global LAnd Surface Satellite, GLASS）产品的光合有效辐射分数（Fraction of Photosynthetically Active Radiation, fPAR）与叶面积指数数据；（2）ERA5全球再分析数据集提供的下行短波辐射、气温与露点温度数据。全球农田分布（包含纯农田像元与农田/自然植被镶嵌像元）源自欧洲空间局气候变化倡议（European Space Agency Climate Change Initiative, ESA-CCI）的土地覆盖/利用分类数据。
本产品采用WGS84坐标系，经纬度投影（EPSG: 4326），数据以GeoTIFF格式存储。每个文件包含一层全球农田范围内的年度农田水分利用效率数据波段。