20. Proportion of Potato Crop that is Irrigated
DH Lister and S Subak

Percentage of the potato crop area in England and Wales that is irrigated  shown in relation to May-August rainfall in England and Wales

Specific indicator
An increasing proportion of the potato crop in England and Wales is irrigated, partly in response to consumer demand but also reflecting perceptions of the risk of summer drought. The specific indicator is the percentage of the potato crop area that is irrigated in England and Wales.
[Source: Ministry of Agriculture Fisheries and Food, Statistics Branch, Foss House, King's Pool, 1-2 Peaseholm Green, York YO1 2PX and Welsh Office, Economic Advice Division, Cathay's Park, Cardiff]

Relevance
Increasingly, supermarkets are demanding consistent supplies of high quality potatoes, which is driving farmers towards increased use of irrigation. Also, potato yields are increased by irrigation, even in wet years. About 46% of potato-growing areas in Britain have provision for irrigation.

Sensitivity to climatic and other factors
A notable increase in the proportion of the potato crop area that is irrigated is evident between 1975 and 1978 and again in most years following 1982. The data after 1982 are a more accurate reflection of actual irrigation, because surveys introduced then asked what area of crop was irrigated in the survey year, whereas previously respondents were asked to identify the area that they usually irrigated in a dry season. Therefore, the rising trend since 1982 represents a real increase in the irrigated area.

This indicator is not correlated with weather conditions, but is perhaps a measure of the responses of farmers and suppliers to the increased risk of summer droughts (experienced in 1976, 1984, 1985, 1990 and 1995) as well as consumer demand.

Change over time
Large investments were made in irrigation equipment following the drought years of 1975 and 1976. Thus, in 1975 only around 12% of the potato crop was irrigated in a dry year, but by 1978 this figure had risen to 21%. From the mid 1970s onwards, there has been a steady increase in the percentage area of the crop irrigated, reaching 46% in 1995 and in the most recent survey year, 2001, 60%.

It is likely that producers without irrigation, especially in much of the eastern and central lowlands of England, will be influenced by an increased incidence of very high (summer) soil moisture deficits, as predicted in climate change scenarios. The percentage of potatoes irrigated may therefore increase further, although this may be moderated by a range of adaptive measures which will reflect the finite nature of water resources in many growing areas, plus the possibility of voluntary and mandatory restrictions on water use. Adaptive measures could include the use of drought resistant varieties, changes in growing schedules to avoid late summer maturation and moves towards cultivation in wetter areas.