Climatological Water Balance
The water balance is a climatological method that accounts for the amount of water in the soil, indicating its availability for plants, and also characterizing the periods considered wet and dry. In general, the inputs of water into the system are: rainfall, irrigation, dew, surface runoff, lateral drainage, and capillary rise. Water outputs can include evapotranspiration, surface runoff, lateral drainage, and deep drainage. The variation in water storage in the soil over a period of time results from the balance of water inputs and outputs in a given volume.
The climatological water balance has several applications in the field of agrometeorology, including: a planning tool in the development of agroclimatic zoning and in determining the best sowing times; and a decision-making tool in rural areas, determining regional water availability and characterizing droughts or periods of excess water.
For climatological studies, it is of interest to quantify the water that will be used by plants. In this case, the method takes into account rainfall and/or irrigation as water inputs into the system. Outputs considered include evapotranspiration and deep drainage, which in the climatological water balance are accounted for as water surplus.
In the figure below, five extracts of climatological water balances are presented, calculated on a monthly basis for a drainage area of 100 square meters, in different regions of the state. In the region of the municipality of Alegre, located in the south of the state, in the Itapemirim River valley, the annual water deficit is 150 mm, occurring from March to November. In December and January, there is a water surplus period of 115 mm. In the region of Venda Nova do Imigrante, a mountainous area of the state, the annual water deficit is approximately 18 mm, concentrated from June to August. The annual water surplus is 550 mm, covering the period from November to May. In the municipality of Ecoporanga, located in the northwest region of the state, the annual water deficit is 120 mm, occurring from April to September. Water surpluses occur in December and January with values of 120 mm. These three locations have the typical water balance of most of the southeastern region of the country, with a dry winter and a rainy summer. The magnitude of the values and the extent of the periods of water deficit and surplus are related to the topographical location of the municipalities. The municipality of São Mateus, on the northern coast, has an annual water deficit of 102 mm from February to September and a characteristic water surplus only in December and January, totaling 20 mm. In Vitória, in the central coastal region of the state, the water behavior is similar, with an annual water deficit of 120 mm and a water surplus of 50 mm.
Climatological Water Balance
