effect of climate change on global potato production, The

American Journal of Potato Research, Jul/Aug 2003 by Hijmans, Robert J

RESULTS

Temperature

According to the climate scenarios considered in this study, the increase in global average temperature will be between 1.2 and 1.8 C in the 2010-39 and between 2.1 and 3.2 C in 2040-69 (Figure 1). This increase is higher than the predicted temperature change weighted by potato area, which is between 0.9 and 1.7 C for 2010-39 and between 1.6 and 3.0 C for 2040-69. When no adaptation of cultivar type and month of planting is allowed between current and future conditions, the potato-area-weighted average temperature change during the potato-growing period is only a little lower than the average temperature change over the whole year (averaged over all climate scenarios a difference of 0.1 C for 2010-39 and 0.2 C for 2040-69). When adaptation of the planting time and cultivar choice is allowed, however, average temperature change during the potato-growing period is much lower than change over the whole year: between 0.6 and 1.1 C for 2010-39 and between 1.0 and 1.4 C for 2040-69 (Figure 1).

Yield

When no adaptation is allowed, overall simulated global potato yields decrease between 10% and 19% in 2010-39, and between 18% and 32% in the 2050s (Figure 2). With adaptation, yields still go down but the decrease is about 40% less: between 5% and 11% in 2010-39 and between 9% and 18% in 2040-69. Adaptation typically consists of a shift of one or two months of the planting time and the use of cultivars that have later foliage senescence in terms of thermal time.

These global aggregate data mask differences between regions. Although simulated potato yields decrease in most regions where the crop is currently grown (Figures 3 and 4), the magnitude of change differs sharply between potato production regions, and is strongly dependent upon whether adaptation is considered or not (compare Figures 3B and 4A and Figures 3C and 4B). Without adaptation, calculated decrease in potential yield is large (> 25%) for many regions, particularly in 2040-69 (Figure 3C). When adaptation is allowed, the effect on yield is lower, except for regions in the tropics.

Changes in yield can in most cases be attributed to temperature change alone (in 90% of the grid cells, radiation contributed less than 10% of the change in yield). Although in some restricted regions changes in yield are strongly influenced by changes in radiation, sometimes induced by changes in cloudiness, but more often because of a shift in planting time.

The moderating effect of adaptation on the temperature during the growing period, and hence on yield, is illustrated in Figure 4C. In some regions, the temperature during the potato-growing period will likely decrease with global warming! (Because higher temperatures will allow a winter crop). Yet in other regions temperature is projected to increase by more than 2 C.

In general, potato-growing regions in the (sub)tropics will suffer the largest decline of potential potato yield, and there is not much scope for adaptation in these regions. Note, however, that some of the worst hit regions (yield decline > 50%) have only very little potato area (Figure 3A). A region with a large potato area and a strong predicted yield decline is a zone from southeast Europe through Russia and Kazakhstan. The regions where global warming would not be a very serious problem, or might be beneficial for potato yield, are mostly at high latitudes, such as regions in Canada, Russia (Siberia), and Scandinavia, where global warming will result in longer (frost-free) growing periods, or at high altitudes in the tropics, such as in the cold highland region of the Peruvian/Bolivian Altiplano. In these regions there is much land that is currently climatically unsuitable for potato production that will become suitable with global warming. Adaptation is particularly important in parts of southern China where higher temperatures increase the opportunity for winter cropping. These findings are farther illustrated by the averages broken down by country (Table 2).