Mapping the spatial distribution of volumetric irrigation water requirements for maincrop potatoes in England and Wales

A procedure has been developed for mapping the spatial distribution of irrigation water requirements for maincrop potatoes in England and Wales using a geographic information system (GIS), The maps take into account crop, climate and soil factors, together with current land use and the proportion of the crop irrigated in each county. The annual irrigation needs (mm) were determined for maincrop potatoes on three contrasting soil types at 11 representative weather stations, using an irrigation scheduling computer model. The results were correlated to available national datasets on soils, climate, current land use, and irrigation practice within a GIS model to generate irrigation need (mm) and volumetric (m(3)) water requirement maps at 5 km resolution. The total net volumetric irrigation water requirements for England and Wales in a 'design' dry year such as 1990 (fifth driest in 20) are estimated to be 61 x 10(6) m(3) for all maincrop potatoes currently irrigated. This compares with previous estimates of 40 x 10(6) m(3) and government agricultural census returns suggesting 51 x 10(6) m(3) were actually applied in 1990, when some restrictions were in force. By overlaying boundaries, the volumetric requirements could be assessed for selected river catchments, aquifers or administrative areas, The effects of changes in land use and irrigation practices could also be modelled to predict future irrigation water requirements. Potential applications of this methodology for water resource management are discussed.