Warming trends and shortened growing seasons: integrating four decades of observations and model simulations to develop wheat adaptation strategies in semi-arid Pakistan.

Climate change is increasingly affecting wheat phenology and productivity in semi-arid regions. This study assessed the impact of long-term climate warming on wheat developmental stages, yield, and management options in rainfed systems of Pakistan. Fourty one years (1980–2020) of phenological (days to anthesis and maturity), yield, and meteorological data (minimum and maximum temperature, and rainfall) were analyzed for two locations: Islamabad (33.67° N, 73.12° E) and Chakwal (32.93° N, 72.86° E). Growing degree days (GDD) were calculated using cardinal temperatures of 4 °C (base), 13.2 °C (optimum), and 35 °C (ceiling). Cumulative GDD ranged from 1,679 to 2,637 °C-days at Chakwal and 2,000–2,500 °C-days at Islamabad. Increasing mean temperatures (18.0 °C at Chakwal and 17.8 °C at Islamabad) were associated with accelerated crop development, reducing days to anthesis (from 127 to 70 days at Chakwal and 133 to 74 days at Islamabad) and maturity (from 155 to 85 days at Chakwal and 163 to 93 days at Islamabad). Consequently, grain yield declined from 2.0 to 1.5 t ha⁻¹ at Chakwal and from 2.3 to 1.4 t ha⁻¹ at Islamabad. Simulated sowing date scenarios showed that early sowing avoided heat stress, whereas delayed sowing caused yield losses of up to 27% at Islamabad and 25% at Chakwal. The results indicate that advancing sowing to 1–15 October and adopting climate-resilient wheat cultivars informed by process-based models can help mitigate warming-induced yield losses.