Geoscience Reference
In-Depth Information
(a)
(b)
BASIN PRECIPITATION
(excluding storage, interception and other losses)
Evapotranspiration
Transpiration
ATMOSPHERE
Input
Precipitation
Interception
INFILTRATION
VEGETATION
CHANNEL
PRECIPITATION
OVERLAND
FLOW
INTERFLOW
(subsurface
stemflow)
GROUNDWATER
FLOW
Stemflow and
throughfall
Overland flow
floods
SURFACE
RAPID
INTERFLOW
DELAYED
INTERFLOW
CHANNEL
STORAGE
Capillary
rise
Infiltration
Channel
flow
Channel
flow
Channel
flow
Channel
flow
SOIL
MOISTURE
Interflow
SURFACE
RUN-OFF
SUBSURFACE
RUN-OFF
Percolation
Capillary
rise
GROUND
WATER
Base flow
recharge
QUICKFLOW
(direct run-off)
BASEFLOW
(base run-off)
Runout
TOTAL RUN-OFF
(streamflow at basin outlet)
Output
OCEAN BASINS
Evaporation
Source: After Ward (1975)
the United Kingdom for general water balance purposes
- and usually reflects a country's remoteness and eco-
nomic 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 69·4
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 cooled to dew-point temperature on contact with cold
surfaces (dew, hoar frost and rime ice). This also identifies
precipitation by
type
as a function of temperature and
creates patterns determined by climatic zone, altitude,
Stream flow
Total
Surface
Stable
% land
% global
Continent
P
E
Q
(flood)
(base flow) area
Q
Q
E
Q
F
Europe
7·17
4·06
3·11
2·05
1·06
7·7
6·5
43·2
65·8
Asia
32·69
19·50
13·19
9·78
3·41
32·0
30·0
40·3
74·1
N. America
13·91
7·95
5·96
4·22
1·74
18·6
12·6
42·8
70·1
S. America
29·36
18·98
10·38
6·64
3·74
12·9
26·5
35·3
63·9
Africa
20·78
16·56
4·22
2·76
1·46
22·3
18·7
20·4
65·2
Australasia
6·41
4·44
1·97
1·50
0·47
6·5
5·7
30·7
76·1
Total
110·32
71·49
38·83
26·95
11·88
100·0
100·0
35·5
69·4
Source: In part after L'vovich (1979).
Notes: P, precipitation; E, evaporation; Q, stream flow; Q
E
, percentage of precipitation discharged as stream flow Q
F
, percentage stream flow
discharged as surface flood or quickflow. Total values of Q
E
and Q
F
are global mean values.
