3.1. Redundancy index analysis
A total of 315 hydrological indices of magnitude, frequency, duration,
timing, and rate of change have been calculated which characterize the
hydrological series in NPRS for different periods of the year (Table
A3). The PCA showed an inertia ranging between 36.2 and 38.0% for the
first axis and between 16.3 and 16.9% for the second (Fig. 2), reaching
approximately 70% when grouping the first five components for the
thresholds of 0, 1, 2, and 5 l/s. Results revealed multiple linear
correlations between indices. It is also noted that the indices of
frequency and duration of zero flow had a positive correlation with the
first axis, while flow magnitude had a positive correlation association
with the second (Fig. 2).
(Here Fig. 2)
Additionally, the first indices with the highest loading coefficient
associated with the first, second and third dimensions were frequently
the same, only changing for the fourth and fifth dimensions for the
different thresholds (Table C1). Consequently, only 171 indices were
selected for the redundancy index analysis based on clusters with
correlation distance between hydrological indices within the same
attribute (magnitude, frequency, duration, timing and rate of change) in
different thresholds (Table C1 and Fig. C2 to Fig. C7). As a result of
the dimensionality reduction and the redundancy analysis, five
hydrologic indices were selected: number of days per year without flow
(DU035), annual percentage of months without flow (FE052), mean daily
annual flows (MA001), CV of Julian date of the annual start of zero flow
(TI002) and annual rise rate (RC001) (Table 1).
(Here Table 1)