Modeling Climate Change Impact on Variety-Specific Wheat Sowing and Adaptation Using DSSAT-CERES Simulation in Nepal’s Central Terai

Wheat is a major source of food and income in Nepal’s Terai region, but its production is threatened by rising temperature and erratic rainfall. However, reliable, site-specific estimates of climate change impacts and practical adaptation options remain limited for the Central Terai region. This study evaluated the impacts of climate change on yields of wheat and tested practical adaptation strategies using the DSSAT-CERES simulation. The model was calibrated and validated using historical weather data (1990–2022), four seasons of field data (2018–2022), followed by yield simulations under downscaled CMIP5 climate projections under RCP 4.5 and 8.5. A randomized complete block design was used for the field trials to evaluate varietal response to standard irrigation, and fertilizer application. The Bhrikuti, Gautam, NL 1311, R 21, and VIJAYA wheat varieties were taken as varietal treatments because these are the most widely adopted wheat varieties in the region. Treatments were replicated over four consecutive years (2018-19, 2019-20, 2020-21, and 2021-22). The model simulated and observed yields, with R² of 0.914 and 0.786 during calibration and 0.861 and 0.755 during validation. The simulation yields were highest for Bhrikuti and Gautam, while VIJAYA yielded the lowest. The sensitivity analysis illustrated the effect of climatic parameters such as Tmax, Tmin, solar radiation, and CO2 concentration on tillering number, maturity date and its yield. The maximum temperature was the most sensitive variable, followed by the minimum temperature, while solar radiation had the smallest effect. A rise of 3°C in the maximum temperature at tillering reduced the simulated yield by approximately 34% and 28% at the anthesis stage. Moreover, CO2 had a substantial effect on the yield increasing by up to 50% and 60% at 500 and 720 ppm respectively. On adaptation simulation, shifting the sowing date gave variety-specific results: early sowing lowered yield in all varieties, while a delay of approximately 15 to 30 days from the usual mid-November date favored Gautam and NL 1311. The results show that DSSAT-CERES can support region-specific planning for wheat in the Central Terai, and matching variety choice with an adjusted sowing window offers a low-cost adaptation to reduce the yield loss expected under warming.