Precipitation, mostly rains, has a huge impact on agriculture. For plants to grow, they need at least a small amount of water, and rain is still one of the most effective ways of watering despite the development of modern technologies.
Too much or too little precipitation is bad and even harmful for agricultural plants. Drought can destroy the harvest and increase erosion, and overly humid weather can trigger the growth of unfavourable fungi. Also, different kinds of plants demand different amounts of precipitation. For example, some succulent species require little water, while tropical plants need hundreds of inches of rain a year just to continue living.
The fluctuation in precipitation amounts is quite substantial in continental climates. They fluctuate more in a month than during a year. A considerable variation in precipitation leads to situations where drought takes place during the years with low amounts, thus forming areas of unstable hydration. With a long absence of rains and at high temperatures, the reserves of moisture in the soil dry out due to evaporation.
A previous arid season brings a shortage of crop yield even in a humid season, as the harvest lacks enough time for ripening. Thus disadvantageous conditions for ordinary plant development are established, and the crop yield of agricultural plants decreases or perishes.
Along with precipitation amounts, the number of days with precipitation in a month or a year is also a significant climatic index. Plants are sensitive to whether a given precipitation amount falls all at once during just a few days, or it rains often and the amount is distributed comparatively evenly throughout a month. For instance, even one great downpour in a prairie area in summer has little ability to improve an arid situation.
By employing a data set of precipitation amounts and a number of days, one can calculate an accumulated precipitation amount for any region during a specific period of time.