Norman J. Rosenberg

Sensitivity of some potential evapotranspiration estimation methods to climate change

A simulation approach was used to generate estimates of the sensitivity of potential evapotranspiration (ETp) to climate change using eight alternative ETp estimation methods. The methods, which differ in structure and data requirements, were: Thornthwaite, Blaney-Criddle, Hargreaves, Samani-Hargreaves, Jensen-Haise, Priestley-Taylor, Penman, and Penman-Monteith. The simulations were performed using climate data from five sites in the North American Great Plains. The results indicate that the methods differ, in some cases significantly, in their sensitivities to temperature and other climate inputs. The degree of agreement among the methods is affected, to some extent, by location and by time of year. When two GCM-derived scenarios of climatic change were applied, the predicted response of ETp varied in magnitude and in some cases in sign, according to the estimation method used. The differences among methods can be attributed both to differences in their sensitivities to climate, and to differences in the climatic factors they consider. The implications of these findings for studies of climatic change are discussed.

Adaptation of agriculture to climate change

Preparing agriculture for adaptation to climate change requires advance knowledge of how climate will change and when. The direct physical and biological impacts on plants and animals must be understood. The indirect impacts on agricultures resource base of soils, water and genetic resources must also be known. We lack such information now and will, likely, for some time to come. Thus impact assessments for agriculture can only be conjectural at this time. How-ever, guidance can be gotten from an improved understanding of current climatic vulnerabilities of agriculture and its resource base, from application of a realistic range of climate change scenarios to impact assessment, and from consideration of the complexity of current agricultural systems and the range of adaptation techniques and policies now available and likely to be available in the future.

Greenhouse warming: Abatement and adaptation

This book focuses on two possible paths of living with a changing climate--abatement and adaptation. The adaptation path is well represented in the book, with chapters on responses to rise in sea level, future agricultural adaptations, Third World agriculture, possibilities presented by currently unmanaged forests, and water resource management. Although the adaptation discussions suggest that adaptive steps will be very difficult and very expensive unless the rate of climate change is slowed, abatement processes are much less well represented in the book. Climate scientists, here and elsewhere, do not report any estimates of how large a decrease in the emissions of infrared-trapping gases would be required in order to slow the climate heating rate by some amount. Only one chapter in the book discusses details of an abatement strategy, that of planting new forests to sequester carbon dioxide and so reduce the annual atmospheric increase. Beyond the discussion of forests, the only consideration of abatement is in a chapter on the use of an economic model to project future carbon dioxide emissions.

Preparing the erosion productivity impact calculator (EPIC) model to simulate crop response to climate change and the direct effects of CO2

The adaptation of a crop simulation model to deal with the impacts of rising CO2 and climate change is described in this paper. Algorithms that represent the direct effects of atmospheric CO2 on crop photosynthetic efficiency and water use were developed for use with the erosion productivity impact calculator (EPIC), a mechanistic crop simulation model. Representative farms were designed to reflect the major cropping systems in the MINK (Missouri-Iowa-Nebraska-Kansas) region and data were assembled to simulate them in EPIC. Climate data were compiled to represent conditions under the control (1951–1980) and analog (1931–1940) climates. Actual daily temperature and precipitation data from a number of climatological stations across the MINK region were used in the simulations. Daily values of solar radiation, relative humidity, and wind speed were simulated stochastically from monthly First Order Weather Station records.

Evapotranspiration in a greenhouse-warmed world: A review and a simulation

Abstract The ways in which the greenhouse effect may affect evapotranspiration ( ET ) rates are briefly reviewed. ET may change because of atmospheric warming and because of associated changes in other climatic factors. ET rates may also be altered by the stimulation of plant growth and increase in stomatal resistance that occur in response to CO 2 enrichment of the atmosphere. The Penman-Monteith model of evapotranspiration was employed with data from four different ecosystems to estimate the possible range of changes in ET which may occur in response to the climatic and plant changes mentioned above. The climatic and plant factors were first varied individually to determine model sensitivity. These factors were then varied simultaneously according to scenarios of climatic change to determine their combined impact on ET . Depending on the ecosystem and on climatic conditions, ET can differ by −20 to +40% from the control case (no climate or plant change).

Simulations of crop responses to climate change: effects with present technology and currently available adjustments (the ‘smart farmer’ scenario)

Abstract If climate changes, farmers will have to adapt to a new set of climate constraints. In this paper we examine the efficacy of strategies for dealing with climate change that are currently available to farmers and that are inexpensive to use; we refer to this group of strategies as ‘adjustments’. Adjustment schemes of various kinds were identified for us by agricultural experts in the Missouri-Iowa-Nebraska-Kansas (MINK) states. These can involve changes in land use, changes in variety and crop selection, changes in planting and harvesting practices, and changes in fertility and pest management. Using the erosion productivity impact calculator (EPIC) model on a small set of representative farms, we tested adjustments of these kinds. The simulations show that earlier planting, longer-season cultivars and the use of furrow diking for moisture conservation would offset some of the yield losses induced by climate change in warm-season crops. Longer-season varieties of wheat (a cool-season crop) and shorter-season varieties of the perennials wheatgrass and alfalfa were also effective. The adjustments to climate change diminished yield losses in all crops but irrigated wheat. Despite the positive effects of adjustments, however, yields of all dryland warm-season crops remained lower than control levels. The adjustments also increased demand for irrigation water. Carbon dioxide enrichment had the same incremental effect on crop yields with or without adjustments (see the fourth paper in this issue), except in the case of alfalfa and sorghum, where a CO 2 -adjustment interaction was found. We conclude that currently available techniques would partially offset the yield reductions caused by a 1930s-like climate, but that in most crops the yield reductions would still be substantial.

Validation of EPIC model simulations of crop responses to current climate and CO2 conditions: comparisons with census, expert judgment and experimental plot data

Abstract A crop simulation model must first be capable of representing the actual performance of crops grown in any particular region before it can be applied to the prediction of climate change impacts. Erosion productivity impact calculator (EPIC) simulations of crop productivity in the Missouri-Iowa-Nebraska-Kansas (MINK) region under the 1951–1980 climate were compared with the US Department of Agricultures ‘County Yield Estimates’ data (averaged over 1984–1987), with expert estimates of yields for each ‘representative’ farm and with the results of agronomic experiments reported in the literature. Most EPIC-simulated yields agreed to within ±20% with USDA reported yields and expert estimates, although there were some outliers. EPIC-simulated yields, evapotranspiration and water use efficiency fell well within the range of experimental results. Perfect agreement with observed crop performance was not a requisite nor should it have been expected. We judged the EPIC simulations sufficiently reliable to justify use of the model in simulating the effects of climate change on crops.

Simulations of crop response to climate change: effects with present technology and no adjustments (the ‘dumb farmer’ scenario)

Abstract The climate of the 1930s—our analog of climate change—was imposed on farms representative of agriculture in the Missouri-Iowa-Nebraska-Kansas (MINK) region through the erosion productivity impact calculator (EPIC) model. Two levels of atmospheric CO 2 were considered: 350 and 450 ppm. No attempts to adjust or adapt the farms to the climate change were made. Results from simulations under the analog climate (1931–1940) were compared with results from simulations under the control climate (1951–1980). EPIC-simulated yields of warm-season crops were reduced by the analog climate. Yield reductions ranged from 7% for irrigated corn to 25% for dryland and soybeans. Simulated yields of dryland wheat were, on the whole, unchanged by the analog climate. Crops under irrigation fared better than dryland crops, although irrigation demand increased markedly. The simulated loss of crop yields under the analog climate was due to truncated growing seasons accompanied by reduced evapotranspiration. The higher level of atmospheric CO 2 alleviated simulated yield losses for all crops, although for corn and soybeans, particularly, yield losses remained significant.

The MINK methodology: background and baseline

A four step methodology has been developed for study of the regional impacts of climate change and the possible responses thereto. First the region’s climate sensitive sectors and total economy are described (Task A, current baseline). Next a scenario of climate change is imposed on the current baseline (Task B, current baseline with climate change). A new baseline describing the climate sensitive sectors and total regional economy is projected for some time in the future (Task C, future baseline, year 2030) in the absence of climate change. Finally, the climate change scenario is reimposed on the future baseline (Task D, future baseline with climate change). Impacts of the climate change scenario on the current and future regional economies are determined by means of simulation models and other appropriate techniques. These techniques are also used to assess the impacts of an elevated CO2 concentration (450 ppm) and of various forms of adjustments and adaptations.

Decadal Climate Information Needs of Stakeholders for Decision Support in Water and Agriculture Production Sectors: A Case Study in the Missouri River Basin

Many decadal climate prediction efforts have been initiated under phase 5 of the World Climate Research Programme Coupled Model Intercomparison Project. There is considerable ongoing discussion about model deficiencies,initializationtechniques, anddatarequirements,but not muchattentionis beinggiventodecadal climate information (DCI) needs of stakeholders for decision support. Here, the authors report the results of exploratory activities undertaken to assess DCI needs in water resources and agriculture sectors, using the Missouri River basin asa case study.This assessmentwas achievedthroughdiscussionswith 120 stakeholders. Stakeholders’ awareness of decadal dry and wet spells and their societal impacts in the basin are described, and stakeholders’ DCI needs and potential barriers to their use of DCI are enumerated. The authors find that impacts, including economic impacts, of decadal climate variability (DCV) on water and agricultural productioninthebasinaredistinctlyidentifiableandcharacterizable.Stakeholdershaveclearnotionsabouttheir needs for DCI and have offered specific suggestions as to how these might be met. However, while stakeholders are eager to have climate information, including decadal climate outlooks (DCOs), there are many barriers to the use of such information. Thefirst and foremost barrier is that the credibility of DCOs is yet to be established. Second, the nature of institutional rules and regulations, laws, and legal precedents that pose obstacles to the use of DCOs must be better understood and means to modify these, where possible, must be sought. For the benefit of climate scientists, these and other stakeholder needs are also articulated in this paper.