Environmental Engineering Reference
In-Depth Information
Plate 14.1
Accumulation on the Taku glacier, Alaska, is
calculated as water-equivalent mass, melted from cores from
the annual snowpack. Density increases with depth and
includes ice storm layers (darker bands).
Photo: Ken Addison.
for general water balance purposes - and usually reflects a country's remoteness and
economic development. Table 14.1 shows key water balance data for the continents,
excluding glacial Antarctica and Greenland. Percentage data for global land area and
river discharge (
Q
) reveal lower shares of river flow for continents with substantial
deserts. A mean value of 69ยท4 per cent discharged rapidly after rainfall or melt events (
Q
f
)
underlines the volatility of stream flow and the maintenance of a substantially lower
base
flow
for much of the year.
Precipitation
volume
determines the gross water balance. It comprises
falling
precipitation (rain, snow, hail) and
direct deposition
which occurs when moist air is
