Aquifer recharge Total volume of water added from the outside to the zone of saturation of an aquifer through the natural water cycle. Artificial groundwater recharge Total volume of water added from the outside to the zone of saturation of an aquifer through artificial recharge only. Actual evapotranspiration Total volume of evaporation from the ground, wetlands and natural water bodies and transpiration of plants. According the definition of this concept in hydrology, the evapotranspiration generated by all human interventions is excluded, except un-irrigated agriculture and forestry. The 'actual evapotranspiration' is calculated using different types of mathematical models, ranging from very simple algorithms (Budyko, Turc-Pyke, etc.) to schemes that represent the hydrological cycle in detail. Please do not report potential evapotranspiration (i.e. "the maximum quantity of water capable of being evaporated in a given climate from a continuous stretch of vegetation covering the whole ground and well supplied with water"). Actual external inflow Total volume of actual flow of rivers and groundwater, coming from neighboring territories. Total actual outflow Actual outflow of rivers and groundwater into the sea, plus actual outflow into neighboring territories. Areal precipitation Total volume of atmospheric wet precipitation (rain, snow, hail, etc.). Snowpack Volume of snow accumulated and stored over a period which can result (fully or partially) in snow melted water. It does not include the glaciers, and it is measured at a reference time.