This study aims to investigate the seasonal variation in growth and physiology of Chlorella sorokiniana UCAM 001 strain using annual optimization monitoring with a groundwater medium in two outdoor flat-plate photobioreactors (PBRs), which were first scaled up at the Faculty of Sciences Semlalia (Marrakech, Morocco). The culture medium was adjusted to ensure non-limiting nutrient concentrations (10 mg center dot L- 1 and 100 mg center dot L- 1 of additional phosphorus and nitrate, respectively). Temperature, light, and algal growth were monitored daily. Proline, glycine betaine, and catalase levels were measured every four days to assess the degree of algal stress. Biomass productivity increased during spring, reaching 30 mg center dot L- 1 center dot day- 1 with a specific growth rate of 0.73 day- 1. However, no growth was observed during the summer. Physiological analysis revealed increased proline and glycine betaine levels during autumn and winter due to temperatures as low as 13 degrees C. In contrast, catalase concentration peaked in spring. Pearson correlation analysis indicated that nutrient limitation, together with temperature and light intensity, induced stress in C. sorokiniana, stimulating catalase production. Algal growth efficiently removed nutrients from the medium, achieving removal rates of 97 % for total phosphorus and 87 % for total nitrogen. Optimized cooling systems will improve PBR efficiency and support algal growth under extreme summer conditions.