Spatial and Temporal Variations in Precipitation and Aridity Index Series of Turkey
211
degree of low-frequency fluctuation at some stations. Significant decreasing trends
showed up in the annual precipitation series of 15 stations and in the winter
precipitation series of 14 stations, mostly over the Mediterranean region. Summer
rainfall series tended to increase significantly in 7 stations. The annual and winter
precipitation anomalies of 17 and 31 stations, respectively, had a significant positive
L-ISC. Spring precipitation anomalies of 18 stations depicted a significant negative
L-ISC. The Markov type persistence showed up in the winter precipitation series of
11 stations.
When the additional analysis on the spatial and temporal variations of normalized
precipitation anomalies for the 1994-2000 period was taken into account, it has been
found that a marked recovery period characterized by near normal and/or above
normal precipitation conditions occurred during the mid-late 1990s (1994-1998) over
most of the country, except the Continental Eastern Anatolia region. Immediately
following this recovery period, much of Turkey, except the western and middle parts
of the Black Sea region and partly Continental Central Anatolia, have experienced
another dry period lasting up to now, including January of 200 I. As a result of last
period of drier than normal precipitation conditions, water stress and shortage reached
a critical point again in Turkey, for not only agricultural and energy production but
also water resources including irrigation, drinking water and other hydrologic systems.
For the period 1930-1993, there has been a general tendency of a shift from humid
conditions during the 1960s to the dry sub-humid climatic conditions of the early
1990s, in the aridity index series of many stations in Turkey. Significant downward
trends in the AI series show up at the stations of the Mediterranean region. At some
stations of the Aegean part of the Mediterranean region, there is a significant change
from humid conditions to dry sub-humid or semi-arid conditions. Aridity index series
of the Black Sea rainfall region are mostly characterized by spectral peaks with cycles
shorter than 3 years. Relatively frequent peaks occur at shorter periods of2.2-2.3 years
(QBO) particularly at the eastern Mediterranean stations, and at longer periods of 1520 years at rest of the Mediterranean stations. At the stations of the MRT region,
shorter cycles of2.S-3.5 years in which 3.0-3.3 year periods are significant, 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 index series. QBOs with the cycles of 2.5-2.6 years at
Eski~ehir and 2.1-2.2 years at Diyarbakrr exceed the 0.95 confidence limits of the
'white' noise continuum.
The Continental Mediterranean region and continental interiors of Turkey could
be aridlands that are affected by desertification processes, owing to the climatic factors
that may lead to the desertification. Climatic factors would include existing semi-arid
and dry sub-humid climatic conditions, long-lasting summer dryness of the air and
soil, particularly in the Continental Mediterranean region with high temperature, high
precipitation variability, and low and erratic rainfall amount. Significant trends
towards drier than normal conditions in annual and winter precipitation, and towards
dry sub-humid or semi-arid climatic conditions may have been increasing
desertification processes in the Mediterranean region of Turkey. When other natural
(especially geomorphologic and pedologic) and anthropogenic factors, such as forest
fires, recent miss-use of agricultural lands and, are also taken into account, this region
could be considered as areas that may be more vulnerable to desertification processes
211
degree of low-frequency fluctuation at some stations. Significant decreasing trends
showed up in the annual precipitation series of 15 stations and in the winter
precipitation series of 14 stations, mostly over the Mediterranean region. Summer
rainfall series tended to increase significantly in 7 stations. The annual and winter
precipitation anomalies of 17 and 31 stations, respectively, had a significant positive
L-ISC. Spring precipitation anomalies of 18 stations depicted a significant negative
L-ISC. The Markov type persistence showed up in the winter precipitation series of
11 stations.
When the additional analysis on the spatial and temporal variations of normalized
precipitation anomalies for the 1994-2000 period was taken into account, it has been
found that a marked recovery period characterized by near normal and/or above
normal precipitation conditions occurred during the mid-late 1990s (1994-1998) over
most of the country, except the Continental Eastern Anatolia region. Immediately
following this recovery period, much of Turkey, except the western and middle parts
of the Black Sea region and partly Continental Central Anatolia, have experienced
another dry period lasting up to now, including January of 200 I. As a result of last
period of drier than normal precipitation conditions, water stress and shortage reached
a critical point again in Turkey, for not only agricultural and energy production but
also water resources including irrigation, drinking water and other hydrologic systems.
For the period 1930-1993, there has been a general tendency of a shift from humid
conditions during the 1960s to the dry sub-humid climatic conditions of the early
1990s, in the aridity index series of many stations in Turkey. Significant downward
trends in the AI series show up at the stations of the Mediterranean region. At some
stations of the Aegean part of the Mediterranean region, there is a significant change
from humid conditions to dry sub-humid or semi-arid conditions. Aridity index series
of the Black Sea rainfall region are mostly characterized by spectral peaks with cycles
shorter than 3 years. Relatively frequent peaks occur at shorter periods of2.2-2.3 years
(QBO) particularly at the eastern Mediterranean stations, and at longer periods of 1520 years at rest of the Mediterranean stations. At the stations of the MRT region,
shorter cycles of2.S-3.5 years in which 3.0-3.3 year periods are significant, 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 index series. QBOs with the cycles of 2.5-2.6 years at
Eski~ehir and 2.1-2.2 years at Diyarbakrr exceed the 0.95 confidence limits of the
'white' noise continuum.
The Continental Mediterranean region and continental interiors of Turkey could
be aridlands that are affected by desertification processes, owing to the climatic factors
that may lead to the desertification. Climatic factors would include existing semi-arid
and dry sub-humid climatic conditions, long-lasting summer dryness of the air and
soil, particularly in the Continental Mediterranean region with high temperature, high
precipitation variability, and low and erratic rainfall amount. Significant trends
towards drier than normal conditions in annual and winter precipitation, and towards
dry sub-humid or semi-arid climatic conditions may have been increasing
desertification processes in the Mediterranean region of Turkey. When other natural
(especially geomorphologic and pedologic) and anthropogenic factors, such as forest
fires, recent miss-use of agricultural lands and, are also taken into account, this region
could be considered as areas that may be more vulnerable to desertification processes