Geography Reference
In-Depth Information
Identification of hydrologically homogeneous groups
The results of constrained ordination or redundancy analy-
sis showed that the variation among the 52 basins of
selected multiple flow statistics or multiple responses
(mean annual runoff, coefficient of variation of runoff,
baseflow index, daily flows with 70% and 90% excee-
dance probability, number of days without flow) could be
explained by average annual pan evaporation, average
annual rainfall, median slope and land cover type. The
basin descriptors explained 69% of the variability of the
flow statistics (Table
11.16
). Therefore, the identification
of hydrologically homogeneous regions had to be based on
these basin descriptors that explain the hydrological
responses. Hierarchical cluster analysis aimed at identify-
ing hydrologically homogeneous regions was therefore
done using these basin descriptors.
Table 11.16. Proportion of variance of flow characteristics
explained by basin descriptors
0.90
0.80
0.70
Percentage
explained
Cumulative
percentage
Catchment characteristic
0.60
0.50
Average annual pan
evaporation
Average annual rainfall
LC
CG
LC
WD
S
50
51
51
0.40
9
4
4
2
60
64
67
69
0.30
0.20
0.10
0.00
LC
CG
is proportion of the basin with wooded grasslands and
grasslands, LC
WD
is proportion of the basin with woodlands.
S
50
is slope for which 50% of the pixels in the basin have
values equal to or less than this value.
0.0
2.0
4.0
6.0
8.0 10.0
Median slope (%)
12.0
14.0
16.0
18.0
20.0
Figure 11.73. Influence of slope on baseflow index (BFI).
2.5
3.0
C25 Obs
C25 Neural Network
C25 Exponential model
D6 Observed
D6 Neural network
D6 Exponential model
2.5
2.0
2.0
1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.0
0.0
0.2
0.4
Exceedance probability
0.6
0.8
1.0
0.0
0.2
0.4
Exceedance probability
0.6
0.8
1.0
3.0
3.0
E72 Observed
E72 Neural network
E72 Exponential model
E49 Observed
2.5
2.5
E49 Neural network
E49 Exponential model
2.0
2.0
1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.0
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Exceedance probability
Exceedance probability
Figure 11.74. Comparison of flow duration curves based on observed daily flows and those predicted using an exponential model and a neural
network for C25, D6, E49 and E72.
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