**4. Climate elements controlling phenology**

Temperature, solar radiation, and water availability are assumed to be the key factors that control plant phenology [4]. However, not only these climatic factors. Indeed, temperature is an inevitable factor on which depends all the chemical reaction and mainly those occurring inside cells of living organism. In addition the temperature is both a characteristic of live and an indispensable condition to survive. Some biological functions and reaction may be inhibited or stopped by cold like in hibernation and dormancy. The solar radiation is unequivocally source of energy which is transformed from it luminous form to the chemical form (ATP) by the photosynthesis in the chlorophyll within plants. Furthermore, sun light is factor to fixate the calcium, to product vitamin and the duration of insolation which is called photoperiod determines the season of fall, season of bud bursting and blooming. Precipitations are source of water for crops. Water is indispensable for any form of life on earth. Indeed water is the solvent in all physiological solution in living organisms. As well as it transmits nutrients and regulates temperature of bodies of living beings.

In fact all the climate with its elements and their features including duration, frequency and intensity are influencing phenophases and living beings lives whence the elaboration of the discipline of bioclimatology.
