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Forecasting the Likely Impacts of Climate Change on Indiana Agriculture

Gerald Shively, Professor; Otto Doering, Professor; Noah Diffenbaugh, Assistant Professor, Department of Earth and Atmospheric Sciences; Laura Bowling, Assistant Professor, Department of Agronomy; Christian Krupke, Assistant Professor, Department of Entomology; Bryan Pijanowski, Associate professor, Department of Forestry and Natural Resources; Jeff Holland, Assistant Professor, Department of Entomology and John “Barny” Dunning, Associate Professor Department of Forestry and Natural Resources

Editor’s note: This article is excerpted from a larger reported entitled Climate Change in Indiana: Initial Analyses of Impacts and Opportunities. The report was released to the Indiana Congressional delegation on February 5, 2008 by the Purdue Climate Change Research Center.


Indiana is among the top US producers of corn and soybeans. Under all likely climate scenarios, the corn belt will remain the best area in the United States for corn and soybean production and Indiana will maintain its position as a top producer of these crops. The state also has important production of other crops, and also of poultry and livestock. Predicting the impact of climate change on these systems is somewhat more difficult because less research attention has been focused on these parts of the agricultural industry.

The major climate-related drivers of agricultural outcomes will be changes in (i) atmospheric CO2 and nitrogen, (ii) temperature, (iii) precipitation, (iv) pests and pathogens, and (v) extreme events.

  • Projected increases in temperature will increase the length of Indiana’s growing season. This, combined with increases in atmospheric CO2 and nitrogen will increase the productivity of most annual crops, including corn and soybeans. Livestock populations may be stressed due to higher temperatures, especially during warmer summer months.
  • The distribution of precipitation across the year is expected to shift, leading to wetter winters and dryer summers. In addition, the inability of rainfall to compensate for increased heat may lead to more drying. This is likely to be most pronounced in summer, leading to dryer soils and more drought-like conditions. To the extent the agricultural industry is unable to compensate through the development of improved genetic varieties that exhibit drought tolerance, productivity will decline. Although one might expect irrigation to fill water needs, given current crop genetics, and associated rates of crop evapotranspiration, investments in irrigation infrastructure are not likely to compensate for the combined forces of greater heat and less moisture. As a result, the key adaptation mechanisms for farmers will be to shift planting dates and adopt crop varieties with shorter growing seasons so as to avoid the hottest parts of the growing season. Farmers will have to avoid the deleterious effects of climate change and take advantage of climate conditions that are more conducive to crop growth. Heavier rainfall and periodic flooding during planting and harvest periods may lead to crop losses.
  • Climate changes are likely to allow more successful overwintering of several pests and diseases, and to also allow for the expansion of pests and pathogens. Heat and moisture stress can make crops and animals more susceptible to pests and diseases. To some extent, improvements in crop and animal genetics may compensate.
  • Increases in extreme rainfall and heat events are likely. These will stress crop and livestock systems above and beyond the impacts listed above. Extreme rainfall events may lead to greater soil erosion and agricultural runoff, with concomitant increases in off-site damages associated with sediment, nutrient, chemical, and pathogen loads.
  • Although perennial systems (e.g. fruit trees and grape production) are not a large part of Indiana agriculture, they are locally important in some areas. By virtue of their permanent nature, producers may find it more problematic to adjust their production practices. As a result, these systems may be more vulnerable to the stresses outlined above.
  • Technology responses, especially development of new crop genetics, will be key factors shaping the future of Indiana agriculture. The pace of climate change relative to the rate of technological change will be an important determinant of agricultural impacts and outcomes.

Crop Phenology

To study crop growth we used a crop simulation model combined with climate scenarios from the well-know Hadley climate simulation model. This simple crop growth model is used to assess changes in earliest planting date and growing degree days. Earliest planting dates are based on when air temperature has been greater than 50°F (10°C) for 5 or more days, soil temperature has been greater than 12°F (12.8°C) for 3 or more days, and soil moisture has been less than field capacity for 3 or more days. Additionally, rain cannot occur on the date of planting. Growing degree days are based on accumulated temperatures in excess of 50°F, and must exceed 1250 for typical corn crops.

Changes are best interpreted relative to the model base climatology; in general there is little difference between alternative climate change scenarios by mid-century. Planting dates show the greatest change in the northern part of the state, probably due to changes in soil moisture. Possible planting dates move forward by about 1 week by mid-century and by 1-2 weeks by century’s end. Changes in crop maturity dates follow the patterns and magnitudes of planting changes: by mid-century maturity advances by 5-10 days.

Total growing season length (gdd10, accumulated until soil frost) increases by 200-400 degree-days by mid-century and 400 degree-days by century end.

Besides some problems with the model predicting crops not getting planted in some years, these preliminary simulations also had difficulty triggering harvest in almost all years for all periods. This suggests that hydrometeorological prediction of harvest needs significant work, but may also indicate potential problems with adequate drying of crops under future climate scenarios. Additionally, these simulations did not account for changes in hybrids or crop types that might result from adaptation to climate changes.

Effects of Temperature Extremes

Changes in the distribution of daily temperature and precipitation events can lead to widespread changes in the exceedance of critical thresholds (White et al. 2006, Diffenbaugh et al. 2007, Trapp et al. 2007). Indeed, recent modeling of the effects of 21st-century climate change on agriculture suggest that changes in the occurrence of severe events could be the primary driver of crop response, with agricultural yields showing little sensitivity to projected changes in mean growing season temperature and heat accumulation but dramatic sensitivity to the coincident changes in temperature extremes (White et al. 2006).

Agricultural Pests

Many of the most important agricultural pests are insects, along with many species that pollinate crops, increase soil fertility through decomposition, and prey upon crop pests. Insect pests reduce US crop production by 13% for an annual loss of $33 billion (USBC 1998). The increase in plant stress predicted with climate change will lead to reduced plant resistance to insect herbivores and an increase in crop loss. Because different aspects of the climate are not expected to shift in the same way (Williams et al. 2007), the impact on agriculture can not be easily forecast (Paine et al. 1998). For example, increased CO2 levels can increase the losses of soybean to the invasive Japanese beetle (Hamilton et al. 2005). The large majority of our crop pest insects are invasive species. The exotic insects such as soybean aphid and the emerald ash borer that successfully invade the Midwest are those that come from similar climates. An altered climate regime in Indiana could invite an entirely new suite of invasive insects that we currently have no knowledge of. Forest insect pests, such as the gypsy moth, defoliate trees during the early summer. When combined with the stress of drought, trees are known to die (Pijanowski 1994). Warmer winter temperatures can also decrease forest pest over-wintering morality in turn increasing the pest population levels during the summer (Sharov et al. 1999). In Indiana, loss of trees on private forest lands could have a large economic impact.

We have quantified the potential impacts of future climate change on a suite of Indiana corn pests (Diffenbaugh, Krupke, et al., in preparation). We find that the distribution of these pests expands in Indiana for those pests that are not already prevalent throughout Indiana. In particular, the migratory taxa – armyworm and corn earworm – become substantially more prevalent in the future climate, transitioning from rarely or never present to commonly present. This expansion is driven by decreases in the occurrence of severe cold events, allowing these taxa to overwinter in Indiana. These migratory taxa happen to be the most cosmopolitan in their infestations, raising the possibility that the risk of infestation would likely increase for other crops in addition to corn should greenhouse gas concentrations continue to rise.


Diffenbaugh NS, Pal JS, Giorgi F, Gao X (2007) Heat stress intensification in the Mediterranean climate change hotspot. Geophysical Research Letters 34:L11706, doi:11710.11029/12007GL030000.

Doering OC, Randolph JC, Southworth J., and Pfeiffer RA (Eds.). 2003. Effects of Climate Change and Variability on Agricultural Production Systems. Kluwer Academic Publishers, Norwell, MA.

Hamilton JG, Dermody O, Aldea M, Zangerl AR, Rogers A, Berenbaum MR, and Delucia EH (2005) Anthropogenic changes in tropospheric composition increase susceptibility of soybean to insect herbivory. Environmental Entomology 34: 479-485.

Paine RT, Tegner MJ, and Johnson EA (1998) Compounded perturbations yield ecological surprises. Ecosystems 1: 535-545.

Pijanowski, B. In prep. Rates and Patterns of Land Use Change in the Upper Great Lakes States, USA.

Sharov, A., B.C. Pijanowski, A. Liehbold and S.H. Gage. 1999. What affected the rate of Gypsy Moth (Lepidoptera: Lymantriidae) spread in Michigan: Winter temperature or forest susceptibility? Agriculture and Forest Entomology 1:37-45.

Trapp RJ, Diffenbaugh NS, Brooks HE, Baldwin ME, Robinson ED, Pal JS (2007) Changes in severe thunderstorm environment frequency during the 21st century caused by anthropogenically enhanced global radiative forcing. Proceedings of the National Academy of Sciences 104:19719-19723.

USBC (1998) Statistical Abstract of the United States 1996. 200th ed. Washington, DC: U.S. Bureau of the Census, U.S. Government Printing Office.

Williams AL, Wills KE, Janes JK, Schoor JKV, Newton PCD, Hovenden MJ (2007) Warming and free-air CO2 enrichment alter demographics in four co-occurring grassland species. New Phytologist 176:365-374.


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