Monthly crop water use simulated for period 1981-2021

Description of the dataset

The dataset provides monthly crop water uses for 26 crop types and period 1981-2021 simulated at 5 arc-minute resolution using the Global Crop Water Model GCWM (Siebert and Döll, 2010; Meza et al., 2021) distinguishing irrigation water use (blue water) and use of precipitation water stored in the soil (green water). Water uses are provided for 26 irrigated and rainfed crops in m³. 

GCWM simulates for each crop a daily soil water balance to estimate evapotranspiration and runoff. Evapotranspiration is calculated according to the Penman-Monteith approach as implemeted in the FAO Irrigation and Drainage Paper 56 (Allen et al., 1998) using ERA5 global reanalysis data (Hersbach et al., 2020; Copernicus Climate Change Service, Climate Data Store, 2023) as climate input. The original hourly ERA5 data were first aggregated to daily data and then disaggregated from 15 arc-minute resolution to 5 arc-minute resolution by using a digital elevation modell and assuming a temperature difference of 0.65 K per 100 m altitude difference. The land use is according to the MIRCA2000 dataset (Portmann et al., 2010) distinguishing 26 irrigated and rainfed crop types. Specific sub-crop classes were used to account for multiple cropping (e.g. different growing seasons of rice) or different growing seasons of temperate cerelas (e.g. spring barley and winter barley). Consequently, the model setup is considering climate variability and climate change but assumes a static land use centered around year 2000. The green water use of irrigated and rainfed crops is the amount of water evapotranspirated under rainfed conditions reflecting the impact of drought on actual evapotranspiration. Blue water use of irrigated crops is the amount of water that would be needed to maintain potential evapotranspiration of irrigated crops. 

Technical specifications

The data available for download consist of ascii-grids at global extent and 5 arc-minute resolution (4320 columns x 2160 rows) with a header of 6 lines. For each of the 26 crops a separate zip-archive is provided to reduce the size of the single files. In total, 1476 ascii-grids are provided for each crop (41 years x 12 months x 3 water use types). Three water use types are distinguished: blue water use of irrigated crops, green water use of irrigated crops and green water use of rainfed crops. When a crop is not growing in a specific grid cell or month, water use will be 0. Water uses are reported in m³ per grid cell. To convert water uses from m³ per grid cell to mm per grid cell please use the ascii-grid containg the cell area of the grid cells in ha and the following equation:

Water use (mm) = 0.1 * Water use (m³) / Cell area (ha).

More details with regard to file names and crop types are provided in the readme file available in the download section.