Analysis and assessment of the current changes of the Caspian Sea climate
S.K.Monakhov O.I. Kholina
"Research Center of Southern Seas Ecology" Ltd.
Key words: Caspian Sea, current climate change, analysis and assessment, methods and
results
Introduction
Currently the 2nd Report on the State of the Caspian Sea environment is being prepared
under the umbrella of the Interim Secretariat of the Tehran Convention. One of the Report
sections will be devoted to the current changes of the Caspian Sea climate change. In this
respect, the publication of the relevant materials on the website of the Coordinating
Committee on Hydrometeorology of the Caspian Sea (CASPCOM) is timely and can be used
for the preparation of the 2nd Report. The objective of the report is to give an overview of
the approach used in CASPCOM materials for the analysis and assessment of climate change,
and to present some of the results obtained while implementing the approach.
Materials and methods
The materials for the analysis and assessment of the current climate change were based on
annually updated CASPCOM data catalogues: catalogues of air and water temperature,
surface
runoff and sea level, most of which date back to 1961 (some of them even earlier).
CASPCOM data catalogues include the data provided by hydrometeorological services of all
the five Caspian littoral states.
In the course of the analysis, the time series were smoothed by moving 30 year periods (1st
derived series), then annual anomalies were calculated as a difference between the mean
(monthly and/or annual) value of a parameter in the current year and for the previous 30
years (2nd derived series). The next step was to determine the annual increments as a
difference between the following and the previous values (3rd derived series) and smoothing
of this series by moving 30 year periods (4th derived series). To analyse the changes in the
amplitude of annual anomalies and increments, them modulo series were used (5th and 6th
derived series).
All the derived series were visualized and approximated by linear and non-linear (polynomial)
trends. The statistical validity of the linear trends was assessed by Student's and Fisher's
methodologies using different significance levels (0.1; 0.05; 0.01). To assess
annual anomalies
and increments, it is important to calculate quartiles, which allows subdividing them into
weak, moderate and strong. Conducting comparative assessment of the growth rate of the
climatic parameters can be implemented for n years, where n equals 0, 15, 20, 25, 30, 40,
and 50
years
Results and discussion
According to CASPCOM data, the ongoing global warming has affected the Caspian Sea area,
where the average air temperature for the past 30 years (1987 - 2006) has grown in
comparison to the mean temperature for 1961-1990 from 9.9 to 10.7
о
С in Astrakhan, from
12.2 to 12.5
о
С in Makhachkala and from 12.7 to 13.5
о
С in Derbent. In the first thirty-year
intervals of the period under study, the average temperature fell slightly (by 0.1 - 0.2
о
С).
Long-term positive linear trend of air temperature (an example
is set by the graph made by
observations
data
in
Derbent)
http://www.caspcom.com/files/climate/climate_en/Air_temperature/Derbent/1_air_temp.p
df
is statistically valid, but the significance level is low (р=0.10).
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CASPCOM materials contain data on annual air temperature anomalies on the Caspian Sea
coast starting from 1991. According to CASPCOM data, air temperature anomaly was
generally positive in all the years starting from mid 1990s. In some years (1997, 2003, 2011)
the anomaly was close to zero (weakly positive or weakly negative), but in Derbent, for
instance, it was positive during all the years starting from
1995.
http://www.caspcom.com/files/climate/climate_en/Air_temperature/Derbent/2_anom
alia.pdf
We should also note positive air temperature anomaly during 2012-2016, though its
value in these years was not so significant as in 2010.
Smoothed by moving 30-year periods, the rate of air temperature increment is increasing.
The linear trend which approximated this increase is statistically valid at p=0.01
http://www.caspcom.com/files/climate/climate_en/Air_temperature/Derbent/6_temp_30.p
df
According to the data of Derbent HMS, the average rate of air temperature increment for
the past 30 years amounted to 0.07
о
С. An obvious fact is that when the
averaging period
increases (up to the past 50 years) or reduces (to the past 10 years), the mean rate of air
temperature increment decreases, and it is negative for the 5 past years (2012-2016)
http://www.caspcom.com/files/climate/climate_en/Air_temperature/Derbent/7_temp_n.pd
f
It points to the deceleration of the Caspian Sea climate warming in the recent years.
According to CASPCOM data, the Caspian Sea water temperature in 1961-2016 was rising as
fast as the air temperature above the sea area (CASPCOM data catalogues include the data of
coastal observations of the temperature of the sea water surface layer). In particular, in
Makhachkala area in 1986-2015, it measured on average 12.9
о
С, which is by 0.4
о
С more than
the average for the period of 1961-1990.
http://www.caspcom.com/files/climate/climate_en/Water_temperature/Makhachkala/1_w
ater_temp.pdf
The positive linear trend is statistically valid at р=0.01 (by Student) and р=0.1
(by Fisher).
However the time series of water temperature anomalies is different from that of the air
temperature. Stable positive anomalies of water temperature were observed only
throughout 1997-2007; before and after this period positive anomalies alternated with
negative ones.
http://www.caspcom.com/files/climate/climate_en/Water_temperature/Makhachkala/1_w
ater_temp.pdf
Smoothed by moving 30-year periods, the rates of water temperature increment, despite the
positive linear trend, are not so convincing as the rates of air temperature increase (which is
confirmed by the statistical estimate). Only the 30-year periods which fell in 1968-2009
interval were characterized by positive water temperature increment rate. Before and after
this period the increment rate varied from positive to negative and vice
versa
http://www.caspcom.com/files/climate/climate_en/Water_temperature/Makhachkala/
6_temp_30.pdf
According
to the data of Makhachkala HMS, the average rate of sea water temperature
increment for the past 30 years amounted to 0.06
о
С. Similarly to air temperature, when the
averaging period increases (up to the past 50 years) or reduces (to the past 10 years), the
mean rate of water temperature increment falls, and it is negative for the past 5 and 10
years.
http://www.caspcom.com/files/climate/climate_en/Water_temperature/Makhachkala
/7_temp_n.pdf
This fact points to the deceleration of the Caspian Sea climate warming in the
recent years.
Throughout 1961-2015, the curve of the Volga flow smoothed by moving 30-year periods
points to its continuous growth and the
following decrease, though the linear trend
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