Global Water Maps

A global water map is a coverage of the earth that describes the state of water circulation in a phase of the hydrologic cycle. This information can be published as a map showing the state of the water variable at a particular point in time, or charted as a time series showing the temporal variation of that variable at a point in space. Such maps can be created through the NASA Land Data Assimilation System (LDAS) for precipitation, evaporation, soil moisture, and other parameters describing the vertical exchange of water between the land and atmosphere, through a combination of observations and simulation modeling. Point observations of water variables such as precipitation and streamflow are carried out by local hydrologic measurement agencies associated with a particular area. These point observations are now being published as web services in the WaterML language and federated using the Global Earth Observing System of Systems to enable the publication of water observations maps for these variables. By combining water maps derived from LDAS with those from federated point observations, a deeper understanding of global water conditions and movement can be created. This information should be described in a Hydrologic Data Book that specifies the information content of each of these map layers so that they can be appropriately used and combined.