Climate change has induced significant alterations in the timing of phenological stages of fruit trees globally, underscoring the critical need for studies incorporating precise quantitative data into biomathematical models describing phenology. Despite numerous regional studies, the pear tree (Pyrus communis L.) has received scant attention in the southern hemisphere. This study focuses on establishing day intervals for key phenological stages – bud burst, flowering, and harvest – in pear varieties including Abate Fetel, Coscia, and Forelle. Monomolecular phenology models were developed for each cultivar, where the determination coefficient (r2) values ranging from 0.94 to 0.96. Additionally, the model validation was conducted to assess accuracy, revealing varying ranges of error metrics among cultivars. The average value of RMSE, MAE, and EF was 9.7, 7.0, and 0.80, respectively. Particularly, Rpo values were consistent, indicating favorable agreement between observed and simulated values. Furthermore, the t-test yielded a value of 1 across all cultivars, confirming model validity. Modeling the effect of climate change to simulate advancement in phenological stages presents a dynamic monomolecular model with lag effect, providing valuable insights to support agricultural management, including pest and disease management, fertilizer application, irrigation, and harvest planning, in response to evolving environmental conditions.