It is the rainfall minus the potential evapotranspiration, adding up the twelve months of the year. Potential evapotranspiration is how much water the environment would evaporate if it were available: it depends mainly on temperature and radiation.
Balance = Precipitación − Evapotranspiración potencial
- Precipitation: the year's rainfall, in mm
- Potential evapotranspiration: the water demand of the atmosphere, in mm
The result says something that rain alone cannot say: whether the water that falls is enough for what the environment requires. A thousand millimeters in Misiones and a thousand in Santiago del Estero are different climates, because in the second the evaporative demand is much higher.
How to read the sign
- Deficit: demand exceeds rainfall. The crop will depend on what the soil has stored, and irrigation becomes a real advantage.
- Balance: between −200 and 200 mm. Transitional regime, typically the western edge of the Pampas region.
- Surplus: excess water. The problem is no longer the dryness and becomes the drainage, the waterlogging and the choice of paddocks heights.
The country's median is a deficit of around 540 mm, which says a lot about Argentina: most of the territory is drier than atmospheric demand demands.