Abstract
Improved crop yield forecasts could enable more effective adaptation to climate variability and change. Here, we explore how to combine historical observations of crop yields and weather with climate model simulations to produce crop yield projections for decision relevant timescales. Firstly, the effects on historical crop yields of improved technology, precipitation and daily maximum temperatures are modelled empirically, accounting for a nonlinear technology trend and interactions between temperature and precipitation, and applied specifically for a case study of maize in France. The relative importance of precipitation variability for maize yields in France has decreased significantly since the 1960s, likely due to increased irrigation. In addition, heat stress is found to be as important for yield as precipitation since around 2000. A significant reduction in maize yield is found for each day with a maximum temperature above 32 °C, in broad agreement with previous estimates. The recent increase in such hot days has likely contributed to the observed yield stagnation. Furthermore, a general method for producing near-term crop yield projections, based on climate model simulations, is developed and utilized. We use projections of future daily maximum temperatures to assess the likely change in yields due to variations in climate. Importantly, we calibrate the climate model projections using observed data to ensure both reliable temperature mean and daily variability characteristics, and demonstrate that these methods work using retrospective predictions. We conclude that, to offset the projected increased daily maximum temperatures over France, improved technology will need to increase base level yields by 12% to be confident about maintaining current levels of yield for the period 2016–2035; the current rate of yield technology increase is not sufficient to meet this target.
Highlights
The yield of most crops has increased over the past several decades
Maize is a widely grown crop in France (Fig. 1) and yields have gradually increased from 0.25 kg mÀ2 to a peak of 0.97 kg mÀ2 over the past 40 years1 (Fig. 2c)
There is no significant trend in precipitation since the 1960s, but variations in maize yields in the 1960s and 1970s seem to be strongly related to precipitation variability (Fig. 2a)
Summary
The yield of most crops has increased over the past several decades. In the most recent decade, yields have stagnated for many crops in several regions, whereas temperatures have generally increased. The reasons for this stagnation are debated, and could include agricultural policy (Finger, 2010), fundamental genetic limits (Calderini & Slafer, 1998), climate (Lobell & Asner, 2003; Brisson et al, 2010), agronomic practice and crop management (Brisson et al, 2010). Crops are known to be sensitive to various aspects of climate.
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