Evapotranspiration: Transfer of water from the Earth’s surface to the atmosphere by evaporation of liquid or solid water plus transpiration from plants.
Precipitation: Water in any form (including rain, snow, hail, sleet, and mist) that leaves the atmosphere and reaches the Earth’s surface.
Change in ice, lakes, snow and soil moisture represent a change from the end of the previous June year to the end of the current June year.
Precipitation and Inflow from other regions represent water gained in the region. All other measures are outflows ie a loss of water.
Water used in hydroelectricity generation is returned to the hydrological system. Discharges match abstraction, meaning that 'net' abstraction is zero.
Information on how much water is gained through precipitation and lost through evapotranspiration summarises the surface component of the water stocks of New Zealand. The data provider derived this from a combination of direct measurement and modelled data.
The data revise and update three previous reports on surface water information. NIWA reran the national TopNet model from July 1994 to June 2014, extended the records of lake volume change and hydroelectric generation water use from recording authorities, and extended the national ice and glacier accounts.