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Attribution of climate change: a methodology to estimate the potential contribution to increases in potato yield in Scotland since 1960


Correspondence: P. J. Gregory, East Malling Research, New Road, East Malling, Kent, ME19 6BJ, UK and Centre for Food Security, School of Agriculture, Policy and Development, University of Reading, Reading, RG6 6AR, UK, tel. + 44 1732 523 711, fax + 44 1732 849 067, e-mail:


Maincrop potato yields in Scotland have increased by 30–35 t ha−1 since 1960 as a result of many changes, but has changing climate contributed anything to this? The purpose of this work was to answer this question. Daily weather data for the period 1960–2006 were analysed for five locations covering the zones of potato growing on the east coast of Scotland (between 55.213 and 57.646 N) to determine trends in temperature, rainfall and solar radiation. A physiologically based potato yield model was validated using data obtained from a long-term field trial in eastern Scotland and then employed to simulate crop development and potential yield at each of the five sites. Over the 47 years, there were significant increases in annual air and 30 cm soil temperatures (0.27 and 0.30 K decade−1, respectively), but no significant changes in annual precipitation or in the timing of the last frost in spring and the first frost of autumn. There was no evidence of any north to south gradient of warming. Simulated emergence and canopy closure became earlier at all five sites over the period with the advance being greater in the north (3.7 and 3.6 days decade−1, respectively) than the south (0.5 and 0.8 days decade−1, respectively). Potential yield increased with time, generally reflecting the increased duration of the green canopy, at average rates of 2.8 t ha−1 decade−1 for chitted seed (sprouted prior to planting) and 2.5 t ha−1 decade−1 for unchitted seed. The measured warming could contribute potential yield increases of up to 13.2 t ha−1 for chitted potato (range 7.1–19.3 t ha−1) and 11.5 t ha−1 for unchitted potato (range 7.1–15.5 t ha−1) equivalent to 34–39% of the increased potential yield over the period or 23–26% of the increase in actual measured yields.