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 Wa les using a geographic information system (GIS), The maps take into ac count crop, climate and soil factors, together with current land use a nd the proportion of the crop irrigated in each county. The annual irr igation needs (mm) were determined for maincrop potatoes on three cont rasting soil types at 11 representative weather stations, using an irr igation scheduling computer model. The results were correlated to avai lable national datasets on soils, climate, current land use, and irrig ation practice within a GIS model to generate irrigation need (mm) and volumetric (m(3)) water requirement maps at 5 km resolution. The tota l net volumetric irrigation water requirements for England and Wales i n 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. T his 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 b oundaries, the volumetric requirements could be assessed for selected river catchments, aquifers or administrative areas, The effects of cha nges in land use and irrigation practices could also be modelled to pr edict future irrigation water requirements. Potential applications of this methodology for water resource management are discussed.