Spatial and Temporal Variations in Precipitation and Aridity Index Series of Turkey
205
Table 2. Number of the stations indicating a significant trend and serial correlation in the annual
aridity index series of 55 stations at the 5 or I per cent level, according to the Mann-Kendall
trend and the L-ISC tests (Tiirke~, 1999), (+): upward trend from the Mann-Kendall test and
positive correlation coefficient from the L-ISC test; (-): downward trend from the Mann-Kendall
test.
Rainfall
Aridity Index
Region
Mann-Kendall Test
Serial Correlation Test
-
, - - - - -
+
-
t
-
BLS
- - - - -... -
. - - - - - , - - - - - - . _ - -
- - - - " - - -
MRT
I
MED
5
3
CMED
I
MEDT
I
1
CCAN
5
2
CEAN
,
I
Total
5
8
by a simple Markov type persistence. Hence, the appropriate 'null' hypothesis
continuum to the spectrum was assumed to be the Markov 'red' noise only for Konya.
The rest of the series of 55 stations, having non-significant positive L-I SC or
significant positive L-I SC without Markov-type persistence and significant but
negative L-ISC, was formulated by a 'white' noise continuum. The 'white' noise
continuum and its 0.90 and 0.95 confidence levels that are plotted superposed on the
spectrum are shown in Fig. 14 for annual AI series of selected stations. The
significant spectral peaks are also specified by their period values in years.
Results of the estimated spectral peaks that exceed the 0.90 and 0.95 confidence
limits of the 'white' noise continuum of the spectrum are not shown in a table, but can
be summarized as follows:
Stations of the Black Sea rainfall region are mostly characterized by spectral
peaks with cycles shorter than 3 years. Spectral peaks having 2.5 year quasi-biennial
oscillation (QBO) deviate from the 'white' noise continuum at the 0.95 confidence
level at the Rize, Samsun and Bolu stations, first two of which are located on the
coastal belt of the Black Sea. In case of significant spectral peaks, relatively frequent
peaks occur at shorter periods of2.2-2.3 years (QBO) at Adana and 2.5-2.6 years at
Dortyol, and at longer periods of 15-20 years at rest of the Mediterranean stations. At
the stations of the MRT region, shorter cycles of2.5-3.5 years in which 3.0-3.3 year
periods are significant at the 0.95 confidence level, and longer cycles of 18-19 years
generally dominate within the observed variations of the aridity index series. Stations
in the CCAN, CEAN and CMED regions have different periodicity in their aridity
205
Table 2. Number of the stations indicating a significant trend and serial correlation in the annual
aridity index series of 55 stations at the 5 or I per cent level, according to the Mann-Kendall
trend and the L-ISC tests (Tiirke~, 1999), (+): upward trend from the Mann-Kendall test and
positive correlation coefficient from the L-ISC test; (-): downward trend from the Mann-Kendall
test.
Rainfall
Aridity Index
Region
Mann-Kendall Test
Serial Correlation Test
-
, - - - - -
+
-
t
-
BLS
- - - - -... -
. - - - - - , - - - - - - . _ - -
- - - - " - - -
MRT
I
MED
5
3
CMED
I
MEDT
I
1
CCAN
5
2
CEAN
,
I
Total
5
8
by a simple Markov type persistence. Hence, the appropriate 'null' hypothesis
continuum to the spectrum was assumed to be the Markov 'red' noise only for Konya.
The rest of the series of 55 stations, having non-significant positive L-I SC or
significant positive L-I SC without Markov-type persistence and significant but
negative L-ISC, was formulated by a 'white' noise continuum. The 'white' noise
continuum and its 0.90 and 0.95 confidence levels that are plotted superposed on the
spectrum are shown in Fig. 14 for annual AI series of selected stations. The
significant spectral peaks are also specified by their period values in years.
Results of the estimated spectral peaks that exceed the 0.90 and 0.95 confidence
limits of the 'white' noise continuum of the spectrum are not shown in a table, but can
be summarized as follows:
Stations of the Black Sea rainfall region are mostly characterized by spectral
peaks with cycles shorter than 3 years. Spectral peaks having 2.5 year quasi-biennial
oscillation (QBO) deviate from the 'white' noise continuum at the 0.95 confidence
level at the Rize, Samsun and Bolu stations, first two of which are located on the
coastal belt of the Black Sea. In case of significant spectral peaks, relatively frequent
peaks occur at shorter periods of2.2-2.3 years (QBO) at Adana and 2.5-2.6 years at
Dortyol, and at longer periods of 15-20 years at rest of the Mediterranean stations. At
the stations of the MRT region, shorter cycles of2.5-3.5 years in which 3.0-3.3 year
periods are significant at the 0.95 confidence level, and longer cycles of 18-19 years
generally dominate within the observed variations of the aridity index series. Stations
in the CCAN, CEAN and CMED regions have different periodicity in their aridity