ALBERT

Description: Recent work suggests that climate change will impact negatively on Canadian prairie wheat through more severe and frequent droughts and increased yield variability, and adaptive strategies have been called for to meet the coming change. However, previous studies have not determined if climate change has already affected wheat yields, nor has the entire prairie region been examined. Using a prairie wheat yield simulation model (PWYSM) at current (constant) technology, it is shown that the weather as it affects wheat, has had a zero trend over the 1900–1988 period. Also, there is no evidence that yield variability has recently increased. Prairie wheat yields therefore appear so far unconnected to the global warming trend this century, suggesting no current need to adapt to a changing climatic regime. Results also show that, at current technology, departures from mean weather may cause decade-long average yield fluctuations as large as ± 10% from the long-term mean, and climate change effects must be detected against this background fluctuation. Also, a 35% decline in actual wheat yields from the first to fourth decades of this century was not matched by deteriorating weather although weather contributed to the decline, and improved yields since 1940 are not explained by better weather. The study of Williams et al. (1988) concluded that a 1930s type dry spell would reduce Saskatchewan wheat yield by 20%, compared to the 1961–1979 mean That applied only to stubble-sown wheat. When adjusted here for the contribution of fallow-sown wheat, the reduction became 16.7%. With Alberta and Manitoba included, the yield reduction for the whole prairie became 13.8% — in good agreement with a 14.0% reduction obtained with the PWYSM. Yield reductions for Saskatchewan are larger than for the prairie as a whole. The reference period chosen also significantly affects findings, and, because the last decade has been relatively unfavourable, PWYSM results show that 1930s type weather would lower mean prairie wheat yield by only 11.0% relative to the 1979–1988 mean. Grain industry decision makers would more likely refer to the last decade than to a more distant period such as 1961–1979, and applying relative yield reductions to the 1979–1988 mean would result in substantial yield underestimates for drought scenarios. Reference periods must be carefully selected for consistent results. Key words: Climate change, wheat yield

Description: Maize (Zea mays L.) was grown outdoors hydroponically and in soil to compare yields in the two systems and to determine the extent to which soil temperature and plant nutrition limit yield of soil-grown plants. The hydroponic system consisted of 22.5-L plastic pails filled with "Turface" to which nutrient solution was added at least twice daily. In all 3 yr dry-matter accumulation throughout the growing season was greater on the hydroponic system than in well-fertilized, irrigated sandy-loam soil when planting pattern and density were the same. Maximum aboveground dry matter and grain dry matter on the hydroponic system were 25.8 and 12.2 Mg ha−1, respectively. It is apparent that there is a soil-based constraint that limits aboveground dry-matter production to 75–85% of the potential with the aboveground environment in the region. Grain yield appears to be limited to a lesser extent. To determine the effect of root-medium temperature, growth in pails buried in the soil was compared to that in soil and in pails placed on the soil surface. Although the temperature of the buried pails was consistently lower than that in the aboveground pails and in the soil, dry matter accumulation was similar to that in the aboveground pails indicating that soil temperature was not a cause of the lower yield of the soil-grown plants. There was no evidence that plants growing on the highly fertilized soil were nutrient limited at any growth stage. Other studies have indicated that transient water stress on soil-grown plants will not explain the difference in growth on the two systems. Key words: Maize, hydroponics, soil limitations, soil temperature, nutrition

Description: Evaporation rates beneath maize canopies were measured using an intact soil core technique. Early in the growing season evaporation rates were periodically high (4.0 mm∙day−1) following rain, but declined rapidly. At full crop cover, when energy supply normally limits evaporation, significant differences in evaporation were detected between canopies with leaf area indices of 3.0 and 4.0. Key words: Evaporation measurement, energy supply, Zea mays L., leaf area, soil evaporimeter, lysimeter

Description: The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence of an "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summer, as a result of large-scale atmospheric feedback triggered by absorbing dust aerosols, rainfall and cloudiness are enhanced over the West Africa/Eastern Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while longwave has the opposite response. The elevated dust layer warms the air over West Africa and the eastern Atlantic. As the warm air rises, it spawns a large-scale onshore flow carrying the moist air from the eastern Atlantic and the Gulf of Guinea. The onshore flow in turn enhances the deep convection over West Africa land, and the eastern Atlantic. The condensation heating associated with the ensuing deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in a northward shift of the West Africa precipitation over land, increased low-level westerly flow over West Africa at the southern edge of the dust layer, and a near surface westerly jet underneath the dust layer over the Sahara. The dust radiative forcing also leads to significant changes in surface energy fluxes, resulting in cooling of the West African land and the eastern Atlantic, and warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at 0.95 or higher.

Description: Version-4 of the Goddard Earth Observing System (GEOS-4) General Circulation Model (GCM) was employed to assess the influence of potential changes in aerosols on the regional circulation, ambient temperatures, and precipitation in four selected regions: India and Africa (current paper), as well as North and South America (companion paper). Ensemble-simulations were carried out with the GCM to assess the aerosol direct and indirect effects, hereafter ADE and AIE. Each simulation was started from the NCEP-analyzed initial conditions for 1 May and was integrated through May-June-July-August of each year: 1982–1987 to provide an ensemble set of six simulations. In the first set, called experiment (#1), climatological aerosols were prescribed. The next two experiments (#2 and #3) had two sets of simulations each: one with 2X and other with 1/2X the climatological aerosols over each of the four selected regions. In experiment #2, the anomaly regions were advectively restricted (AR), i.e., the large-scale prognostic fields outside the aerosol anomaly regions were prescribed while in experiment #3, the anomaly regions were advectively Interactive (AI) as is the case in a normal GCM integrations, but with the same aerosols anomalies as in experiment #2. Intercomparisons of circulation, diabatic heating, and precipitation difference fields showed large disparities among the AR and AI simulations, which raised serious questions about the proverbial AR assumption, commonly invoked in regional climate simulation studies. Consequently AI simulation mode was chosen for the subsequent studies. Two more experiments (#4 and #5) were performed in the AI mode in which ADE and AIE were activated one at a time. The results showed that ADE and AIE work in concert to make the joint influences larger than sum of each acting alone. Moreover, the ADE and AIE influences were vastly different for the Indian and Africa regions, which suggest an imperative need to include them rationally in climate models. We also found that the aerosol induced increase of tropical cirrus clouds would potentially offset any cirrus thinning that may occur due to warming in response to CO2 increase.

Description: A common deficiency of many cloud-physics parameterizations including the NASA's microphysics of clouds with aerosol-cloud interactions (hereafter called McRAS-AC) is that they simulate lesser (larger) than the observed ice cloud particle number (size). A single column model (SCM) of McRAS-AC physics of the GEOS4 Global Circulation Model (GCM) together with an adiabatic parcel model (APM) for ice-cloud nucleation (IN) of aerosols were used to systematically examine the influence of introducing ammonium sulfate (NH4)2SO4 aerosols in McRAS-AC and its influence on the optical properties of both liquid and ice clouds. First an (NH4)2SO4 parameterization was included in the APM to assess its effect on clouds vis-à-vis that of the other aerosols. Subsequently, several evaluation tests were conducted over the ARM Southern Great Plain (SGP) and thirteen other locations (sorted into pristine and polluted conditions) distributed over marine and continental sites with the SCM. The statistics of the simulated cloud climatology were evaluated against the available ground and satellite data. The results showed that inclusion of (NH4)2SO4 into McRAS-AC of the SCM made a remarkable improvement in the simulated effective radius of ice cloud particulates. However, the corresponding ice-cloud optical thickness increased even more than the observed. This can be caused by lack of horizontal cloud advection not performed in the SCM. Adjusting the other tunable parameters such as precipitation efficiency can mitigate this deficiency. Inclusion of ice cloud particle splintering invoked empirically further reduced simulation biases. Overall, these changes make a substantial improvement in simulated cloud optical properties and cloud distribution particularly over the Intertropical Convergence Zone (ITCZ) in the GCM.