The National Center for Atmospheric Research (NCAR) is working in conjunction with a number of universities and research institutions to develop models to enable us to better understand our environment. A major part of this effort is the development of a global model to study the effects of variations in moisture, biogenic emissions  and other physical parameters which affect the Earth's climate. The Climate System Model (CSM) is a fully coupled model with four major component models and a flux coupler. The use of a flux coupler enables the component models to be run in different programming languages,  at different temporal and spatial scales, if required. Thus only processes which are similar in their spatial and temporal scale are grouped together in a given model. The major components of CSM include the following:

• Land Surface Model (LSM) to monitor moisture levels over the land surface
• Atmospheric Model (AM) to monitor atmospheric moisture over the land and sea
• Global Ocean Model (GOM) to monitor moisture levels in the sea
• Sea Ice Model (SIM) to monitor ice formation and melting in the sea

The Center for Research in Water Resources (CRWR) at the University of Texas at Austin, is developing a GIS based runoff routing model to determining how much water the land surface discharges into the ocean. The development of the model is being funded by a National Science Foundation (NSF) grant. The GLOBAL LAND HYDROLOGIC MODEL (GLHM) will use input generated by the Land Surface Model to compute fresh water discharges into the ocean, an input for the Global Ocean Model.

GLOBAL LAND HYDROLOGIC MODEL (GLHM) is being developed in two stages:

• GIS based terrain analysis
• FORTRAN based runoff routing

• which portion of the ocean (or outlet cell) each piece of the land surface drains out of
• how far a drop of water falling on the land surface has to travel to get to the ocean

• Projection file for Africa
• Projection file for Asia
• Projection file for Australasia
• Projection file for Europe
• Projection file for South America
• Projection file for North America

• Inputs include
• hydrologically correct 30" digital elevation models (DEM) and flow direction grids from the USGS
• raw digital elevation models from the USGS (for areas in which hydrologic processing has not been completed)
• LSM meshes for defining zones over which runoff is generated by vertical balance
• 0.5^o meshes for defining ocean cells and land surface cells
• Processing steps include

• defining ocean cells as outputs cells
• computing the watershed for each ocean cell
• defining land polygons as runoff generating units
• computing flow length for land cells

 

• how much water flows from the land surface to each portion of the ocean
• when does the water get to the ocean

• Inputs include
• excess precipitation or runoff generated by LSM through a soil water balance
• a table containing the area, mean flow length and output cell for each land polygon
• a text file containing ocean cell id numbers of all the output cells
• a text file containing the routing parameters (generated by a FORTRAN utility)



• Processing steps include
• convoluting excess precipitation to generate runoff
• computing flow time for each land polygon in terms of time steps
• aggregating flows for each ocean cell, for each time step to generate hydrographs