Summary and Conclusions

Climate change clearly has serious implications for water management in the Sacramento Basin. Based on the results presented above, several conclusions can be drawn which are summarized in Tables 11.9 and 11.10. The Land Use Change scenario (i.e. no climate change) is taken as a reference or business as usual scenario for comparing climate change impacts and adaptation strategies.

First, in terms of agricultural production, it is clear that a certain level of unmet agricultural water demand is unavoidable and that climate change will exacerbate the situation. Unmet agricultural demands increase by about 2.3% from the business as usual scenario when climate change is introduced. This increased unmet demand, however, may be offset by the increased yields of rice (possible increase of up to 50%) and tomato crops (possible increase of up to 20-30%). For instance, given that rice

Fig. 11.11. Groundwater storage at the Sacramento Stone Corral for both the water for environment and integration strategies and Hadley A2 GCM scenario for 2070-2099.

accounts for a modelled agricultural area of 225,000 ha (19% of the total irrigated area in the Sacramento Basin) and assuming that the total unmet demands are distributed proportional to the irrigation requirements and that acreage is a surrogate for production, these yield increases could balance the 2.3% unmet demands under climate change. A key question for further research is to determine the extent to which these increases in water shortfalls (an additional 2.3% in 2010-2039 and 7.4% in 2070-2099) can be offset by increased productivity, stabilizing the overall production and income generated for farmers.

By adopting a policy of food security, unmet agricultural water demand (above the reference) decreases from 2.3 to 1.7% for 2010-2039, a relatively small impact. Similarly, for 2070-2099, the Water for Food strategy shows a reduction in the amount of unmet demand by a little over 1%. However, what is gained by such a strategy in both periods is a reduction in the variability in these unmet demands. Thus, such strategies are important mechanisms for effectively reducing the inter-annual risk farmers face in terms of agricultural production. Furthermore, in both time periods, these increases in unmet demands can be offset by the use of groundwater banking, as illustrated in the integration (Water for Food and the Environment) strategy. For the Sacramento Stone Corral, for instance, groundwater banking means that on average all demands are met.

One possible adaptation strategy that was not considered here is the reduction in total agricultural area by switching to higher value crops. Such a policy initiative may make an appreciable difference. Also, there is a ticking time-bomb in the overall water use - in the business as usual and Water for Food strategies, groundwater is being unsustainably mined, and even calls into question whether agriculture would continue to be profitable given the possible pumping costs associated with this mining.

Table 11.9. Effect of adaptations on food and environmental security 2010-2039.

Indicators

Table 11.9. Effect of adaptations on food and environmental security 2010-2039.

Variance in

Domestic

Agricultural

agricultural

Salmon

Wetland

water

Ground

production

production

population

area

supply

water

Adaptations

(1)

(2)

(3)

(4)

(5)

storage

Land use and

-2%

1.1X

-6%

No

-3%

Fast

climate change

increase

change

decline

Water for food

-2%

No

-8%

-5%

No

Fast

increase

change

decline

Water for

-5%

1.6X

-6%

Slight

-2%

Slow

environment

increase

increase*

decline

Integration

-3%

1.3X

-6%

Slight

-2%

No

increase

increase*

decline

(1) Average percentage change in total met agricultural demand from a baseline of 5% unmet demand.

(2) Factor increases above the baseline standard deviation of 328x10® m3.

(3) Percentage change in average met flow requirements. Based on an average of four AFRPs (Yuba River, American River, Feather River and Sacramento River) and Freeport flow requirement.

(4) Average percentage change in total met environmental demand (refuges and wetlands) from the baseline of 0% unmet demand. *The environmental demands for both the Water for Environment and Integration strategies increase by 123x10® m3. Thus, although 2% of these increased demands are unmet, compared to the baseline, effectively there is an increase in total wetland area.

(5) Average percentage change in total met urban demand from the baseline of 6.5% unmet demand.

Groundwater banking provides a solution to this critical issue while improving the availability of supplies during dry season events at the same time.

Groundwater storage will decline as the aquifers are being pumped at rates beyond annual renewable recharge unless some intervention is made. For example, by imposing constraints on the maximum amounts that can be withdrawn from the aquifers in the Water for Environment strategy, the rate of decline is significantly slowed. In the Integrated strategy, groundwater banking is shown to further slow, if not eliminate the rate of decline.

For the environment, it is shown that certain flow requirements related to aquatic ecosystem health (AFRPs) will be difficult to meet (e.g. American River AFRP), while others are relatively easily met (e.g. Feather River AFRP). Strategies that prioritize these flow requirements result in a marginal improvement compared to strategies that prioritize municipal and agricultural demands. With growing stresses on water availability, unmet demands for wetlands and refuges may be as much as 5%, unless the environment is prioritized. These levels of unmet demands may or may not be acceptable depending both on the timing of the deficits (e.g. during critical spawning

Table 11.10. Effect of adaptations on food and environmental security 2070-2099.

Indicators

Table 11.10. Effect of adaptations on food and environmental security 2070-2099.

Adaptations

Agricultural production (1)

Variance in agricultural production (2)

Salmon population (3)

Wetland area (4)

Domestic water supply (5)

Ground-water storage

Land use and

-7%

2.8X

-14%

-1.5%

-5%

Fast

climate change

increase

decline

Water for food

-6%

2.3X

-19%

-5%

- 4%

Fast

increase

decline

Water for

-12%

3.4X

-12%

Slight

-12%

Slow

environment

increase

increase*

decline

Integration

-9%

3.4X

-12%

Slight

-12%

No

increase

increase*

decline

(1) Average percentage change in total met agricultural demand from the baseline of 5% unmet demand.

(2) Factor increases above the baseline standard deviation of 348X106 m3.

(3) Percentage change in average met flow requirements. Based on an average of four AFRPs (Yuba River, American River, Feather River and Sacramento River) and Freeport flow requirement.

(4) Average percentage change in total met environmental demand (refuges and wetlands) from the baseline of 0% unmet demand. *The environmental demands for both the Water for Environment and Integration strategies increase by 123X106 m3. Thus, although 2% of these increased demands are unmet, compared to the baseline, effectively there is an increase in total wetland area.

(5) Average percentage change in total met urban demand from the baseline of 6.5% unmet demand.

periods) and on the social value assigned to the ecosystems. By adopting a Water for Environment strategy or Integrated strategy, wetland areas can be increased. Under these strategies, only approximately 2% of these increased demands are unmet.

The business as usual scenario will result in about 6% unmet urban demand. This is primarily due to counties that draw municipal water from the American River upstream of higher priority flow requirements. Whether or not the flow requirement would be prioritized over municipal demands in the future is unknown, but poses an interesting trade-off question. Unmet urban demands are, in general, higher when the environment is prioritized and lower when food security is prioritized (it is assumed that urban demands would always be satisfied before agriculture, although subject to demand management policies). For instance, by 2070-2099, unmet demands are estimated to increase by 5% above the business as usual case in the presence of climate change. By adopting a Water for Food strategy, unmet urban demands only increase by 4%. But by adopting a Water for Environment strategy, unmet demands increase by 12%.

These results are summarized in Tables 11.9 and 11.10.

The adaptation strategies explored here generally involve making trade-offs between food and environmental security, as is highlighted by Tables 11.9 and 11.10. Under Water For Food, agricultural security improves at the cost of the environment. Similarly, under Water for Environment, shifting water to the environment entails some shift of water out of agriculture. Moreover, the situation worsens in 2070-2099 as climate change effects become more pronounced. Mitigations of trade-offs come into play through the enhancement of productivity of crops due to increased carbon, finding non-water consuming activities to support the economy of the region, and implementation of integration win-win strategies such as groundwater banking.

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