Water resources: long-term annual average

The minimum period taken into account for the calculation of long term annual averages is 20 years. - Actual evapotranspiration is the volume of water transported from the ground (including inland water surfaces) into the atmosphere by evaporation and by transpiration of plants. - Internal flow is the total volume of river run-off and groundwater renewal generated, in natural conditions, exclusively by precipitation into a territory. The internal flow is equal to precipitation less actual evapotranspiration. - Actual external inflow is the total volume of actual inflow of rivers and groundwater coming from neighbouring territories. - Total fresh water resources is the total volume of water that is additionally available due to internal flow and external inflow. - Total actual outflow is the total actual outflow of rivers and groundwater into the sea and into neighbouring territories.