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.).

This is the second of a series of three papers describing the methodology of development of a distributed model for estimating runoff and sediment discharge of ungaged rivers. This paper presents the design of the model which permits its application to watersheds of any size and the obtaining of runoff and sediment time series at any point of the river basin which is being modeled. The model requires inputs which are usually available for most areas and/or can easily be synthesized from secondary sources or by transposition. The model was designed with the aim of keeping the number of model parameters at a minimum. It permits the simulation of the nonlinear response of the watershed elements to the meteorological input. The model calibration and validation were carried out by using data available in a river basin in southern Ontario. A more detailed analysis of the calibration‐validation results is presented in the third paper of the series.

Bouther's theory on actual and potential evaporation can be used as a basis to develop semi-empirical relationships between precipitation, actual evaporation, and radiation. These relationships are curvilinear, and the derived precipitation-runoff relationships are also curvilinear. Since the variation of annual radiation from one year to another in tropicalequatorial regions is not very significant, the average value of annual radiation can be approximated using direct measurements or indirect estimates from data taken over a period of from two to five years. This value can be used with the semi-empirical relationship developed in the paper to obtain fair estimates of the annual variation of actual evaporation and runoff from data on annual precipitation and good estimates of the long-term averages of these hydrologic characteristics. Bouther's theory can be used to analyze evaporation and runoff for periods of less than one year and for estimating lake and reservoir evaporation. However, in this case, the assessment of the effect of heat and moisture storage requires further investigation. (

The need for a distributed numerical model for information transfer on runoff and sediment discharge from a gaged river section to any section of the river or its tributaries is discussed. The methodology of developing the information system, which forms the basic structure for the development of such a model, is briefly described. The advantages of the proposed information system are presented, and suggestions to further improve it are made.

Recent developments in collection and interpretation of remotely sensed back radiation data from the earth surface obtained by satellites has made it possible to readily delineate areas covered by snow on the earth surface. In view of this, attempts have been intensified during the last decade to generate statistical relationships between the snow covered area in a basin and the corresponding runoff during the snow-melt period. However, examination of such relationships developed specifically for forecasting purposes in the Indus River basin in Pakistan indicates that, given the current data and operational constraints, their usefulness is very limited. The need for improving collection of remotely sensed data on snow to obtain information on snow density and other auxiliary information is emphasized.

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