Managing Water Resources in the West Under Conditions of Climate Uncertainty A Proceedings (1991) / Chapter Skim
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7. Effects of Increasing Carbon Dioxide Levels and Climate Change . . .
7. Effects of Increasing Carbon Dioxide Levels and Climate Change . . .
Pages 101-147
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From page 101... ...
for a doubling of the carbon dioxide concentration. The objectives of this paper are to examine plant responses to rising carbon dioxide levels and climatic changes and to interpret the consequences of these changes on crop water use and water resources for the United States.
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where (2) en = the saturation vapor pressure at a given air temperature the actual vapor pressure that exists in the air.
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SOURCE: Adapted from Bennett et al., 1964. Thus, we can see that theory predicts that yield will be proportional to cumulative transpirational water use, divided by vapor pressure deficit.
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This is a second mechanism whereby increased carbon dioxide concentrations may affect plant transpiration. Another effect of rising carbon dioxide concentrations is the change in water-use efficiency (WUE)
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Thus, rising global temperatures would increase transpiration by increasing the atmospheric vapor pressure deficit.
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From page 106... ...
The following sections of this chapter will examine more closely the effects of rising carbon dioxide concentrations and climate change on vegetation, providing qualitative and quantitative assessments of how these changes will affect photosynthesis growth once transpiration water requirements of crops. , , O DIRECT EFFECTS OF CARBON DIOXIDE ON PHOTOSYNTHESIS, TRANSPIRATION, AND GROWTH OF PLANTS Atmospheric Carbon Dioxide The carbon dioxide concentration of the earth's atmosphere has varied throughout geologic time.
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From page 107... ...
Since few agricultural crops are CAM plants, they are not important in the process of managing water resources under conditions of climate uncertainty. Since C4 plants have a mechanism for concentrating carbon dioxide in bundle sheath cells of leaves, their photosynthetic rates
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From page 108... ...
Plant Growth Responses to Carbon Dioxide Increasing atmospheric carbon dioxide levels have caused increasing photosynthetic rates, biomass growth, and seed yield for all of the globally important C3 food and feed crops (Acock and Allen, 1985; Enoch and Kimball, 1986; Warrick et al., 1986; Allen, 1990~. Some plants, such as cucumber, cabbage, and perhaps tomato, have shown a tendency to first increase leaf photosynthetic rates in response to elevated carbon dioxide concentrations, and then to decrease photosynthetic rates after several days.
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c Rint = Y-axis intercept for zero C From the parameters of this equation, photosynthetic rate, biomass accumulation, and seed yield changes of soybean due to carbon dioxide concentration changes can be estimated (Allen et al.,
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From page 110... ...
The relative midday maximum photosynthetic rates under carbon dioxide enrichment were consistently higher than relative biomass yields, probably because the photosynthetic response to elevated carbon dioxide levels is greater under high light conditions than it is under total daily solar irradiance conditions. Transpiration Responses to Carbon Dioxide The effect of carbon dioxide concentration on water use under field conditions has been discussed for many years.
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From page 111... ...
The atmospheric carbon dioxide concentrations that prevailed during the last Ice Age, and from the end of the glacial melt until preindustrial revolution times, were 200 and 270 pan, respectively. 2 The first world energy "crisis" occurred in 1973, when the carbon dioxide concentration was 330 ppm.
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From page 112... ...
The increase in leaf vapor pressure will increase transpiration rates per unit leaf area; thus, the transpiration rates will be maintained at only slightly lower values than would exist at ambient environmental carbon dioxide concentrations. In effect, all of the energy balance factors involved in canopy foliage energy exchange not just stomata!
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(1985) compared water-use efficiencies of soybean canopies grown in outdoor, sunlit, controlled-environment chambers at 800 and 330 ppm carbon dioxide concentrations which had LAI values of 6.0 and 3.3, respectively.
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Clearly, higher LAI values under elevated carbon dioxide concentrations can increase transpiration rates to the point where all of the improved WUE arises from increased photosynthetic rates and none from decreased water use. Finally, it should be pointed out that increases in WUE in a world with higher carbon dioxide levels do not necessarily imply any reduction in crop water requirements per unit area of land.
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These curves were drawn to represent active crop plants in temperate zones. The actual photosynthetic carbon dioxide uptake rates
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The photosynthetic rates of C3 plant leaves increase at elevated carbon dioxide levels because molecules of carbon dioxide compete more effectively with oxygen for binding sites on rubisco, the carboxylating enzyme (Bowes and Ogren, 1972~. When plants are well watered, leaf temperatures tend to rise more slowly than air temperatures throughout the daily cycle, so that foliage-to-air temperature differences become greater as air temperature rises (Idso et al., 1987; Allen, 1990~.
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The duration of each ontogenic phase of plant growth decreases with increasing temperature, which is the most important effect of temperature within the upper and lower limits of survival. INTERACTIVE EFFECTS OF CARBON DIOXIDE AND CLIMATE CHANGE Photosynthetic and Productivity Interactions As explained above, Figure 7.4 shows leaf photosynthetic carbon dioxide uptake rate versus temperature responses typical of C4 plants and C3 plants at carbon dioxide concentrations of 330 ppm.
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From page 118... ...
, previous carbohydrate storage, and stage of growth of the plants may affect the biomass growth ratio during the winter months. We may conclude that increasing both carbon dioxide concentrations and temperature will cause a greater increase in biomass productivity than increasing carbon dioxide levels alone.
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In summary, the biomass growth ratio of plants grown at elevated carbon dioxide concentrations may increase with increasing temperature for vegetative growth, as suggested by Figure 7.4. However, this response may be reversed for seed grain crops that have a determinate growth habit, such as "Bragg" soybean.
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(1985c) for doubled carbon dioxide concentration conditions when leaf area index was very similar for both the ambient and doubled carbon dioxide treatments.
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ESTIMATING YIELD AND WATER REQUIREMENTS OF CROPS UNDER TWO CURRENT CLIMATE CHANGE SCENARIOS General Circulation Models Climate changes under conditions of doubled atmospheric carbon dioxide levels have been predicted using five atmospheric general circulation models (GCMs)
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The possibility of a significant reduction in summer precipitation, coupled with a temperature rise, could pose a serious problem for future agricultural productivity and water resources. Modeling Crop Responses to Carbon Dioxide and Climate Changes Many years of experimental observations on the interactions of carbon dioxide and climate factors would be required to provide complete information on responses of plants to climate change.
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Monthly precipitation data of two sites for baseline climate and derived values for GISS and GFDL scenarios are given in Figures 7.5, 7.6, and 7.7, respectively, for Columbia, South Carolina, and Figures 7.8, 7.9, and 7.10, respectively, for Memphis, Tennessee. These two sites were essentially at the center of two GISS model grid cells and close to the center of two GFDL model grid cells, and thus should be appropriate sites for representing climate change scenarios within the grid cells of the two models.
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. 0 1 2 3 4 5 6 7 8 9 10 1 1 12 13 MONTH FIGURE 7.6 Derived average monthly precipitation and potential evapotranspiration for Columbia, South Carolina, from a GISS climate change scenario for doubled atmospheric carbon dioxide.
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. _ 9 10 11 12 13 7 8 MONTH FIGURE 7.7 Derived average monthly precipitation and potential evapotranspiration for Columbia, South Carolina, from a GFDL climate change scenario for doubled atmospheric carbon dioxide.
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at/ ~ ~1 1 1 1 1 l 0 1 2 3 4 5 ~//\ / . 1 ;.J EVAPOTRANSPIRA~ON l l · - 1 1 1 1 1 1 1 6 7 8 9 10 11 12 13 MONTH FIGURE 7.10 Derived average monthly precipitation and potential evapotranspiration for Memphis, Tennessee from a GFDL climate change scenario for doubled atmospheric carbon dioxide.
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Maize yields declined by only about 8 percent in the GISS climate scenario and by about 73 percent in the GFDL scenario when the effects of climate change due to the greenhouse effect were simulated (Table 7.4~. Although irrigation increased predicted yields, the GISS and GFDL climate scenarios gave yield decreases of 18 and 27 percent, respectively, relative to the irrigated baseline weather crops.
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TABLE 7.4 The effects of climate change only on simulated maize yields (bushels/acre) when the atmospheric carbon dioxide concentration is doubled.
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predicted a 15 percent overall irrigation requirement increase for this region, with greater requirements for alfalfa because its growing season was increased and lower requirements for corn and winter wheat because their growing seasons were decreased. The direct effect of rising carbon dioxide concentrations offset the adverse effects of climate change at some, but not all, locations in the simulations of Ritchie et al.
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From page 130... ...
For example, a 6.3°C rise in GFDL scenario temperature for Mead, Nebraska, resulted in a 42 percent increase in predicted evapotranspiration but only a 23 percent increase when all other climate change factors were also considered. Similarly, a GISS scenario temperature rise of 4.7°C for Konza Prairie, Kansas, gave a 28 percent predicted increase in evapotranspiration, but this increase was only 4 percent when all other climate change factors were included in the Penman-Monteith equation.
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From page 131... ...
However, the climate changes that would occur under the doubled carbon dioxide concentrations used in this simulation may occur at lower carbon dioxide concentrations if radiatively active trace gases other than carbon dioxide play a large role in the greenhouse effect. In that case, the direct carbon dioxide effects would be somewhat lower than those shown in the examples of Tables 7.2 through 7.5 for an equivalent climate change.
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From page 132... ...
Climate change scenarios for Columbia, South Carolina, and Memphis, Tennessee for the GISS and GFDL models were selected to further illustrate the precipitation and temperature change effects on potential monthly and annual evapotranspiration and water deficits or excesses (Pears et al., 1989; Curry et al., l990a,b)
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From page 133... ...
Nevertheless, the potential for recharge and subsequent streamflow was great (528 mm) during the November through April period, so the GFDL scenario has the potential of providing more streamflow water resources than the GISS scenario, although the GISS scenario provides more rainfall for crops and other vegetation during the summer months (Table 7.6~.
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From page 134... ...
Also, during cooler months with higher rainfall, some soil water recharge must occur before rainfall will produce streamflow. The impact of several climate change scenarios on California water resources was summarized by King et al.
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These factors illustrate the vulnerability of the western states' water resources to climate change scenarios that include reduced precipitation. The impacts of reduced precipitation on native ecosystems, rain-fed agriculture, and water supply systems could be equally severe for eastern states.
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In general, the harvest index tends to decrease with increasing carbon dioxide concentration and with increasing temperature. Selection of plants that would use more photoassimilates for reproductive growth seems a useful goal for future research as the atmospheric carbon dioxide concentration increases.
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have shown greater response to carbon dioxide at high average daily temperatures than at low average daily temperatures during vegetative growth across the range of 12 to 35°C. This response is in agreement with single leaf photosynthetic measurements of responses to elevated carbon dioxide across a range of temperatures.
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· Rising carbon dioxide levels will cause an increase of photosynthetic rates, growth, yield, and water use efficiency for C3 crop plants. Water use per unit land area will not change much unless temperatures increase.
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1985. Crop responses to elevated carbon dioxide concentration.
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1989. Effects of projected CO2induced climatic changes on irrigation water requirements in the Great Plains States (Texas, Oklahoma, Kansas, and Nebraska)
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1984. Implications of the Rapidly Rising CO2 Content of the Earth's Atmosphere for Water Resources in Arizona.
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Pp. 57-61, 64 in Proceedings of a Conference on Evapotranspiration and Its Role in Water Resources Management.
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1984. Soybean canopy growth, photosynthesis, and transpiration responses to whole-season carbon dioxide enrichment.
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1987. Large-scale changes of soil wetness induced by an increase in atmospheric carbon dioxide.
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R Lemon, ea., Carbon Dioxide and Plants: The Response of Plants to Rising Levels of Atmospheric Carbon Dioxide.
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R Lemon, ea., CO2 and Plants: The Response of Plants to Rising Levels of Atmospheric Carbon Dioxide.
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1986. General circulation model CO2 sensitivity experiments: snow-sea ice albedo parameterizations and globally averaged surface air temperature.
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