Table 1. Summary of models that estimate global irrigation requirement.
| Global Models | Spatial resolution | Base year | MCP | Precipitation | Reference evapotranspiration | |||
|---|---|---|---|---|---|---|---|---|
| 2021 | This study | 0.0833° | 2000 | yes | 0.25° (d) | 0.25° (d) | HS | |
| 2020 | [12] | WATNEEDS | 0.0833° | 2000(a), 2016 | yes | 0.05° (d), 0.5° (d)* | 0.5° (m) | PM |
| 2011 | [11] | CROPWAT (FAO) | 0.0833° | 2000(b) | no | 0.5° (m) | 0.166° (m-LTA) | PM |
| 2010 | [10] | GEPIC | 0.5° | 2000 | yes | 0.5° (m) | 0.5° (m) | HS |
| 2010 | [9] | GCWM | 0.0833° | 2000(a) | yes | 0.5° (m), 0.166° (m-LTA)** | 0.5° (m), 0.166° (m-LTA)** | PT, PM |
| 2008 | [8] | H07 | 1° | 1991(c) | no | 1° (d) | 1° (d) | SEB |
| 2008 | [7] | LPJmL | 0.5° | 1985(d) | no | 0.5° (m) | 0.5° (m) | PM |
| 2007 | [6] | WATERSIM (IWM) | 0.1° | 2000 | no | 0.5° (m) | 0.5° (m) | PM |
| 2002 | [5] | WaterGAP | 0.5° | 1995 | no | 0.166° (m-LTA) | 0.166° (m-LTA) | PT |
Acronyms and notes used in the table. MCP: Multi-Cropping Practices. Reference Evapotranspiration methods: PM (Penman-Monteith), PT (Priestley-Taylor), HS (Hargreaves-Samani), SEB (Surface Energy Balance). Temporal resolution of data: (d) daily, (m) monthly, (m-LTA) monthly Long-Time Average (1961–1990).
(*) 0.05° in the region between 50°N– 50°S, 0.5° in the rest of the world.
(**) effective resolution of 0.166°, matching the two datasets.
(a) Average result for the period 1998–2002.
(b) Average result for the period 1996–2005.
(c) The assessment provided an average result, using input data for the period 1986–1995.
(d) The map of irrigated crops refers to year 2000. The assessment provides an average estimation using monthly climate data for the period 1971–2000.