Studies on water resources in the last few years have had the tendency to encompass larger and larger areas. The increase in size and sophistication of these studies makes the use of computers almost mandatory. To adapt computers to this type of study, the study area must be converted to a schematic representation which is easily manageable by computers. A simple and reasonable way of doing this is to cover the study area with a square grid, which may then be considered as consisting of a matrix of squares. This system can be used to store, process, and retrieve information and may have numerous applications in the fields of hydrology, hydraulic power, economics, etc. The paper presents the application of the square grid system to the estimation of the precipitation, temperature, and runoff distribution in a large area and shows how the use of the system enables efficient combination of the meteorologic and hydrologic information available in assessing the precipitation, temperature, and runoff distribution. An example of such a computation for a 43,000-squaremile area is shown and the advantages of the method over the usual techniques emphasized. (Key words: Newfoundland; digital computers; runoff; drainage basin characteristics) NOTATIONS A•., Ratio of the area of lakes in the considered grid square to the total square area; An, Ratio of the area of forest in the considered grid square to the total square area; Az, Ratio of marshes in the considered grid square to the total square area; B, Barrier height, defined as the difference between the elevation of the area considered and the highest elevation encountered in the direction for which the barrier height is computed; determined for a square as the weighted average of barrier heights for the center of the square and four points located 4.4 miles apart on a 17.6-mile line having the square center in the middle and perpendicular to the direction for which the barrier height is sought (ft). Bs•, Barrier height in southeast direction (ft). Bs•,, Barrier height in southwest direction (ft); D, Shortest distance to the sea from a meterological station or square center (miles); Ds•, Distance to the sea in southeast direction from a meteorological station or square center (miles); Ds•,, Distance to the sea in southwest direction from a meteorological station or square center (miles); 919 920 SOLOMOAI El' AL. H• G, Index of overburden depth in the square (varying between 1 for no overburden to 3 for overburden over 100 feet deep) estimated from aerial photography; Elevation of meteorologic station or average elevation of the square (feet); Latitude index, expressed as the distance from a parallel line situated at a distance of 43.5 miles south of the outmost southern limit of the island (miles); $, Average slope of the square; P, Mean annual precipitation (in.); R, Mean annual runoff (in.).