Climate warming accelerates maize phenology and reduces water requirements and yields in south-eastern Kazakhstan

This study assesses the impacts of climate change on maize water requirements and yields in south-eastern Kazakhstan, a semi-arid region dependent on meltwater from the Tien Shan Mountains for irrigation. The region is experiencing significant warming, projected to continue, leading to cryosphere degradation and reduced meltwater availability. Using field data collected between 2016 and 2019, two crop–water models (AquaCrop and SALTMED) were calibrated and validated to simulate maize growth, water demand, and yield at a farm located in the Tien Shan foothills under future climate scenarios. Simulations were driven by downscaled and bias-corrected outputs from four Global Circulation Models under Representative Concentration Pathways (RCP) 4.5 and 8.5 for 2020–2049, 2040–2069, and 2070–2099. Results show that continued warming will shorten the maize growing season by 36–38 days (RCP4.5) and 42–45 days (RCP8.5), reducing crop water requirements by 11–15% (AquaCrop) and 16–24% (SALTMED) by 2100 relative to the 1976–2005 baseline. AquaCrop projects a 10–12% yield reduction by 2100, with statistically significant declines by mid-century under both scenarios. SALTMED projects a 7–8% reduction by 2100, with significance emerging in the late century under RCP4.5 and mid-century under RCP8.5. These changes are primarily driven by temperatures exceeding maize’s physiological optimum. The findings align with global evidence of accelerated phenology and reduced maize productivity under climate warming. Adopting efficient irrigation systems, adjusting sowing dates, and selecting shorter-maturing cultivars could help align water demand with peak rainfall and runoff, sustaining yields under declining meltwater availability. • AquaCrop and SALTMED simulated maize yield and water requirements at field scale. • By 2100, maize growth cycle may shorten by 38–45 days due to rising temperatures. • Maize water requirements are projected to decline by 11–24% and yield by 6–11%. • Changes are driven primarily by rising temperatures and accelerated phenology. • Future crops may require less, not more, irrigation water.