Food security

Of the three primary water uses affected by land use changes and climate change, agriculture has the largest unmet demands in terms of quantity, but in terms of percentages, the unmet demands are comparable. Agricultural shortfalls, however, are compensated in part by the increased productivity of certain crops due to increased carbon under climate change. As discussed earlier, field-scale modelling using SWAP shows that rice yields, for example, could increase by as much as 50% in the A2 scenario considered here, and tomato yields could increase by 20%. These numbers assume full irrigation.

As discussed in the previous section, with only land use change, agricultural demand will on average have a 5% shortfall in 2010-2039 and 2070-2099. When climate change is introduced into the system, this number increases to 7% over the 2010-2039 period and 12% over the 2070-2099 period (Table 11.5). This analysis further reveals that from a policy perspective, even if the Sacramento system is managed with a focus on food security (Water for Food strategy), about 7% of the demand will still be unmet in 2010-2039, with an increase to about 11% by 2070-2099. When the focus is on environmental security (Water for Environment strategy), these numbers are higher; almost 10% of agriculture demands are on average unmet in 2010-2039, reaching 16% in 2070-2099. Under the Water for Food strategy, unmet demand is slightly less than the land use and climate change scenario because DSM strategies are imposed on all urban demands, thus additional water is available for agriculture uses. For the B2 GCM climate scenarios, the percentage unmet demands are larger. This is in part due to both larger agricultural demands and less available water in the system.

The potentially higher increase in yields, which vary from 20% to 50%, may in fact compensate for these deficits. It is very difficult to predict however, as world prices may react to this increased productivity, which could result in positive or negative impacts on farmer incomes.

In terms of variability of agricultural production (defined as the variation in

Table 11.6. Variation in unmet demand (106 m3/year) (coefficient of variation).

Adaptation strategy

2010-2039

2070-2099

Land use change

329 (0.68)

348 (0.70)

Land use and climate change

359 (0.46)

959 (0.65)

Water for environment

524 (0.50)

1204 (0.61)

Water for food

337 (0.47)

802 (0.61)

annual unmet demands), the standard deviation of the unmet agricultural demand increases by almost a factor of 3 under the climate change scenario from 2010-2039 to 2070-2099 (Table 11.6). The coefficient of variation also increases. Furthermore, even with the priority given to agriculture in the Water for Food strategy, the dramatic variation in agricultural production cannot be avoided, although it is slightly reduced. The situation is exacerbated under the Water for Environment strategy, where the standard deviation increases to 524 X 106 m3 in 2010-2039 and increases to 1204 X 106 m3 by 2070-2099.

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