Climate Change and Maize Yield in Iowa

Abstract

Climate is changing across the world, including the major maize-growing state of Iowa in the USA. To maintain crop yields, farmers will need a suite of adaptation strategies, and choice of strategy will depend on how the local to regional climate is expected to change. Here we predict how maize yield might change through the 21st century as compared with late 20th century yields across Iowa, USA, a region representing ideal climate and soils for maize production that contributes substantially to the global maize economy. To account for climate model uncertainty, we drive a dynamic ecosystem model with output from six climate models and two future climate forcing scenarios. Despite a wide range in the predicted amount of warming and change to summer precipitation, all simulations predict a decrease in maize yields from late 20th century to middle and late 21st century ranging from 15% to 50%. Linear regression of all models predicts a 6% state-averaged yield decrease for every 1°C increase in warm season average air temperature. When the influence of moisture stress on crop growth is removed from the model, yield decreases either remain the same or are reduced, depending on predicted changes in warm season precipitation. Our results suggest that even if maize were to receive all the water it needed, under the strongest climate forcing scenario yields will decline by 10-20% by the end of the 21st century.

Fig 1. Agro-IBIS simulated maize yield (Mg ha^-1) as driven with CRU data and output from all six GCMs for 1951–2005, and maize yield surveyed by USDA.

Simulated values are averaged over all grid cells in the model domain, and county level observations are averaged over a region corresponding to the model domain. Error bars indicate the range of yield across grid cells (for model simulation) and counties (for survey).

Fig 2. Change in the May-October average air temperature (°C) for each GCM and RCP scenario where the value shown is a difference between MID21 or LATE21 and HISTORIC.

Fig 3. Change in monthly precipitation for May through October for each GCM and RCP scenario where the value shown is a percent difference between MID21 or LATE21 and HISTORIC.

Fig 4. Change in DEFAULT yield (%) vs. change in May-October average air temperature (°C) for each GCM and RCP scenario where the value shown is a difference between MID21 or LATE21 and HISTORIC.

Each point represents the value of a model grid cell (a) or the domain average (b).

Fig 5. Change in NONSTRESS yield (%) vs. change in maize growing period length (days) for each GCM and RCP scenario where the value shown is a difference between MID21 or LATE21 and HISTORIC.

Each point represents the value of a model grid cell.

Fig 6. Change in NONSTRESS yield (%) vs. change in May-October average air temperature (°C) for each GCM and RCP scenario where the value shown is a difference between MID21 or LATE21 and HISTORIC.

Each point represents the value of a model grid cell (a) or the domain average (b).

Fig 7. Change in Yield Loss Index vs. change in summer (JJA) precipitation (%) for each GCM and RCP scenario where the value shown is a difference between MID21 or LATE21 and HISTORIC.