**Abstract**

The witnessed aberrance and irregularities in the timing of pheno-phases is an undeniable evidence of the reality of the climate change and hence proves the complete control of climate over phenology. In fact, some researchers mentioned the advance of blooming and the delay of defoliation to the mid of winter as well as the disappearance of many animal and vegetal species. This would visibly illustrates the impact of climate changes which became a factual reality. These facts a long with the rhythmicity of life under the climate control and seasonality makes the importance of this chapter unequivocal, and a backbone for this very book of "Agrometeorology". Accordingly, this chapter treats each phenophase from dormancy to fructification to cover all the plant life cycle. For each of which we focus on how climate is intimately controlling the biological processes of each life phase and how climatic elements are the strongest and first factor which induces plant to starts the appropriate phenophase according to the fitting season. Plant is indeed very sensitive to seasonal variation in climate elements which induces the transcription of specific genes to produce specific enzymes which to their turn are with specific act on specific cells and tissues. Hence there is a high harmony between plant physiological response and climate seasonality endorsed by the circadian clock which is merely created by the historical subjection of plants to the impact of climate. Nonetheless, the recent climate changes are seemingly to be against this natural harmony between phenology and climate. This should due to their erraticism which may cause damages to the ecosystem and available resources. Thence, this chapter within this book would be inspiring for some strategies of adaptation to the climate changes to avoid such a prejudice against crops by adjusting the agricultural calendar and planting dates to avoid coincidence of fragile phenophases (germination, flowering, and fructification) with climatic hazards.

**Keywords:** phenophase, climate change, agriculture, germination, fructification, food security

#### **1. Introduction**

The autumn is usually called fall due to the featuring fall of leaves during this season as a phenological phenomenon called defoliation. This would figure out how intimately related are seasons and phenology or in other words how strong is the repercussion of climate seasonal variation on the plants and animals successive and cyclic phenomena. Indeed, we almost notice seasons via phenological variation along with climatic one. This deep intimate co-occurrence between climate

and phenology phenomena is very appealing for wonder and consequently to the exploration of the relations and mechanisms of these relations and how living beings respond to climate seasonal variations during their life cycles.

As a matter of undeniable fact, this chapter consists of a core and mandatory knowledge for the agriculture and farmers to make their crops safe and the most productive. Therefore, this chapter is likely to be the backbone for this very book of agro- meteorology and all disciplines within the same scope and the nature and life's scope.

Particularly, in the recent context of climate change. Indeed, Subrahmanyam and Murthy (in Ref. [1]) confirmed that global climate change is a reality, a continuous process that needs to be taken seriously. Many evidences have been gathered to depict that climate change is taking place. And although several species have responded to climatic changes throughout their evolutionary history, there is a concern as to how different ecosystems and populations will respond to this rapid rate of change.

The fact of the book being devoted to agro-meteorology imposes that this chapter should be more specified and oriented towards phenology of plants as to they are the subject of agriculture more than animals. This is also due to another fact that climate impacts plants more than animals. Accordingly, this chapter attempts to explain how climate factors affect and control each pheno-phase within the plant life cycle from dormancy and germination to fructification, after defining all of phenology, phonological phases, climate, climate factors, and climate seasonal variations.
