Adapting irrigated maize cropping to a changing climate

The European Mediterranean region is heralded globally for both its high vulnerability to soil degradation and realization of the climate crisis, with ambient temperatures increasing at rates 20% faster than the global average. Maize crops in this region experience moderate to severe water stress during late spring and summer, although such trends are being exacerbated by lack of agricultural irrigation, which has exhausted ~70% of freshwater reserves to date. Future water scarcity is expected to increase as evaporative demand ramps in line with global warming, with rainfall intensity and distribution becoming more variable, and with intensification of weather extremes including drought. Agricultural droughts occur when soil moisture for a prolonged period is below the wilting point threshold, leading not only to yield reduction or failure, but also impaired soil biogeochemical processes, enhanced losses of terrestrial carbon and soil biodiversity. Thus, agricultural water management is key not only in terms of global food security but also in terms of natural capital and environmental stewardship, namely planning for net-zero greenhouse gas emissions. Here, our aim was to identify adaptations for maize crops that improve water-use efficiency, resulting in greater production for lower water requirement. Using the Agricultural Production Systems sIMulator (APSIM) crop model, we simulated maize growth in 14 regions across the European Mediterranean region under historical (1984-2021) and future (2064-2100) climate horizons, assuming a 22% decrease in precipitation and a 5.6ºC increase in temperature following the Six Assessment Report of the IPCC (IPCC, 2022). Treatments included a range of irrigation quanta per season (0 mm, 200 mm, 400 mm, 560 mm, 920 mm, 1400 mm, 1600 mm and 2000 mm) and several representative irrigation infrastructures. Irrigated water was applied with furrow, sprinkler and drip-irrigation systems. Under future climates, we reveal that penalties in rainfed maize yields range from between 30% to complete catastrophic collapse. Increasing irrigation applied helped alleviate negative impacts of the climate emergency. However, even under optimal irrigation, maize yields decreased by 6-44% (except for modest increases in Villamanan [north Spain] and Montelier [south France]). For the same amount of water applied over the season, drip and sprinkler systems were conducive to greater yields than furrow irrigation (1-63% and 1-52%, respectively), with the rotating sprinkler (pivot) irrigation providing the highest average water use efficiency (10-17 kg grain/mm water). Drip irrigation – characterised by smaller amounts of water applied more frequently for a longer duration - was conducive to higher evaporation losses than pivot and furrow. Understanding the impacts of climate variability under future climates will be critically important for developing productive, profitable, efficient irrigation strategies that improve security of carbon, water and food.

Keywords: Climate change, irrigation management, crop yield, water use efficiency, Mediterranean region