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Numerical simulation of snow hydrology for management purposes Woo, Ming-Ko

Abstract

The objective of this study is to provide a method of estimating snow storage and melt-water release for small coastal mountain basins in the temperate forest zone of southwestern British Columbia. It adopts a numerical simulation approach, using daily precipitation and temperature as input parameters. The data are usually obtainable from 'base-stations’ located in the valleys. Most stations have a short history so that long-term prediction of snow distribution in small basins requires both temporal and spatial extensions of data. Temporal extension involves treating precipitation and temperature first as random variables, and then as inputs to a deterministic evaluation of snow storage. In order to model precipitation, a second-order Markov chain technique is used to simulate the occurrence of wet and dry days, while the quantity of daily precipitation is also generated for wet days. Daily temperature is simulated by linearly superimposing various deterministic and random components of temperature time series. Spatial extension involves a recognition of altitudinal and vegetation cover zones. The extension of precipitation and temperature records from a base-station to other altitudinal zones and to forest sectors is achieved by empirical functions derived from observations at the University of British Columbia Research Forest at Maple Ridge, B.C. With an understanding of precipitation and temperature, it is possible to simulate snow events. For snowfall, a probability matrix based on minimum daily temperature is constructed from data available at the University of British Columbia Research Forest, For snowmelt, a distinction is made between clear-weather and rain melts, and daily maximum temperature and daily rainfall are used to estimate melt-water release. A simulation model is developed to extend daily temperature and precipitation from short-term records. Using the simulated data as inputs, a second model simulates snow-pack storage as the balance between incoming precipitation and outgoing snowmelt in both the forested and the open sectors of each of the several altitudinal zones. The model is tested by comparing one hundred years of simulated temperature, precipitation and snow storage data with historical records, and the correspondence is satisfactory. The model is useful because even when prediction is difficult owing to meagre input data, it is possible with this method to produce long-term estimates of snow resources in small coastal basins.

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