=Paper=
{{Paper
|id=Vol-3293/Hpaper90
|storemode=property
|title=Detecting Changes in Annual Precipitation Trends During the Last Two Climatic Periods (1955-1984 and 1985-2018) in Nestos River Basin, N. Greece
|pdfUrl=https://ceur-ws.org/Vol-3293/paper90.pdf
|volume=Vol-3293
|authors=Nikolaos D. Proutsos,Alexandra D. Solomou,Panagiotis P. Koulelis,Athanassios Bourletsikas,Nikolaos E. Chatzipavlis,Dimitris Tigkas
|dblpUrl=https://dblp.org/rec/conf/haicta/ProutsosSKBCT22
}}
==Detecting Changes in Annual Precipitation Trends During the Last Two Climatic Periods (1955-1984 and 1985-2018) in Nestos River Basin, N. Greece==
https://ceur-ws.org/Vol-3293/paper90.pdf
Detecting Changes in Annual Precipitation Trends During the
Last Two Climatic Periods (1955-1984 and 1985-2018) in Nestos
River Basin, N. Greece
Nikolaos D. Proutsos 1, Alexandra D. Solomou 1, Panagiotis P. Koulelis 1, Athanassios
Bourletsikas 1, Nikolaos E. Chatzipavlis 1 and Dimitris Tigkas 2
1
Hellenic Agricultural Organization “DEMETER”, Institute of Mediterranean Forest Ecosystems, Terma
Alkmanos, Athens, 11528, Greece
2
Centre for the Assessment of Natural Hazards and Proactive Planning & Laboratory of Reclamation Works
and Water Resources Management, School of Rural and Surveying Engineering, National Technical University
of Athens, Athens, Greece
Abstract
Precipitation spatio-temporal changes can have an important impact on natural ecosystems. In
this study, we assess the annual precipitation spatial distribution along with its changes along
two climatic periods (1955-1984 and 1985-2018) in Nestos River (N. Greece), an area that
hosts a variety of ecologically important habitats. The annual data were obtained from nine
long operating stations. For the analysis, the Mann-Kendall and the Sen’s slope methods were
applied to detect the trends, evaluate their significance and estimate the changing rates of
precipitation. Results indicate a high spatial variability of precipitation in the sub-basin with
higher and increasing values during the latest years compared to the past for the mountainous
(northern) part of the basin, whereas the coastal and altitudinal lower (southern) part receive
less precipitation. In the coastal zone, a shift in precipitation is identified from west to east,
with the eastern coastal zone to become more and more rapidly dry compared to the past. This
is critical for the conservation of the valuable but vulnerable priority habitats in the coastal
zone, considering their high water requirements.
Keywords 1
Precipitation trends, Nestos River, Mann-Kendall test, Sen slopes
1. Introduction
Precipitation trends on a global level present high spatial and temporal variability [1]. Today, North
Europe is more humid and the Mediterranean more arid compared to the past, whereas eastern
Mediterranean regions are anticipated to face even more arid conditions in terms of reduced
precipitation within the next years [2]. The precipitation trends in the Mediterranean basin appear to be
generally negative with higher decreasing rates of about -10% in its eastern areas and less intense in the
western part of the basin [3], however this general pattern is characterized by high spatial variability [1,
4-8]. Such changes are expected to have serious ecological impacts considering that the Mediterranean
basin is characterized as both a biodiversity and a climate change hotspot [9, 10]. A reduction in
precipitation may impose significant changes in net productivity and plants growth dynamics affecting
highly the natural rain-fed ecosystems [11, 12]. In addition, long-term monitoring may portray the
potential of trees’ recovery in case of climatic vagaries [13].
Proceedings of HAICTA 2022, September 22–25, 2022, Athens, Greece
EMAIL: np@fria.gr (A. 1); solomou@fria.gr (A. 2); pkoulelis@fria.gr (A. 3); mpat@fria.gr (A. 4); nickxpal@yahoo.com (A. 5);
ditigas@mail.ntua.gr (A. 6)
ORCID: 0000-0002-8270-2991 (A. 1); 0000-0002-0014-1909 (A. 2); 0000-0002-9050-0783 (A. 3); 0000-0003-2696-2622 (A. 4); 0000-
0002-2001-259X (A. 6)
©️ 2022 Copyright for this paper by its authors.
Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR Workshop Proceedings (CEUR-WS.org)
456
In Greece, recent climate is more arid compared to the past [14, 15]. Proutsos et al. [16] assessed
precipitation trends by analyzing data of the period 1951-2006 obtained from 32 gauged stations in
Greece and found significant decreasing annual trends, in most cases, with an average changing rate of
–3.7 mm/y, with high seasonal and spatial variability. The precipitation trends are generally negative
and more intense in the islands [17, 18], whereas in the continental areas are less intense and even
become positive during the last years [19]. In N. Greece, Stefanidis and Alexandridis [20], detected
decreasing but insignificant precipitation trends for Pertouli, whereas positive trends were found in
Taxiarchis forest sites. Proutsos et al. [21] also studied the precipitation trends in the coastal area of
Nestos Delta (N. Greece) and found statistically significant decreasing trends mainly at lower altitudes,
and increasing higher.
The present study is based on the study of Proutsos et al. [21] focused on the identification of
precipitation trends in Nestos Delta for the period 1956-2017, which was based on precipitation data
from five meteorological stations. In this study, we have expanded the analysis by assessing annual
precipitation time series from nine rain gauge stations inside and nearby Nestos’ River Greek sub-basin
and we performed the analysis separately for two climatic periods (1956-1984 and 1985-2017) in order
to identify and evaluate the different changing spatial patterns of the annual precipitation during the
latest climatic period compared to the respective changes in the previous one.
2. Study Area, Data and Methods
Nestos (Mesta) is transnational river, with its sources in southern Bulgaria (Rila mountains). It flows
about 126 km in Bulgaria and about 130 km in Greece, whereas the total catchment area is 5,613 km²
[22]. The Greek part of the basin (Figure 1) hosts a variety of crops, and also natural ecosystems with
high ecological interest. Forested parts of the basin are strictly protected as Natura 2000 sites, with most
significant the fan-shaped Nestos Delta [23], which extends to an area of about 23,000 ha. The Delta is
considered one of the most important wetlands of Greece, due to its size and the variety of habitats (28
types) located inside the protected area [24], among which three of them are characterized as of high
priority: 1150* (coastal lagoons), 3170* (Mediterranean temporary ponds) and 91E0* (Alluvial forests
with Alnus glutinosa and Fraxinus excelsior). More information about the site can be found in Proutsos
et al. [25].
Figure 1: Aspect of Nestos River in N. Greece.
457
The climate in the broader area is humid according to UNEP’s [26] climate zone aridity classification
system based on Thronthwaite’s [27] aridity index AI [14, 15], whereas precipitation changes have been
occurred during the last 50 years with decreases in the coastal zone and increases in the mountainous
area [21], indicating that in the coastal zone, the natural vegetation, is anticipated to be more vulnerable
in case of climatic vagaries in the future.
For this study, annual precipitation data series of nine gauged stations were used (Figure 2, Table
1). The analysis was performed for two distinct climatic periods: 1955-1984 (1st climatic period) and
1985-2017 (2nd climatic period) on an annual time step. For each data series the Mann-Kendall test [28,
29] was applied to detect the trend and identify the level of significance. The Mann-Kendall test is a
non-parametric method, widely used in trend analysis of hydroclimatic data [16, 30-35] and is
considered as a reliable tool in identifying monotonic linear and non-linear trends in non-normal
datasets [36]. The trends slopes (Q) were estimated by the Sen’s method [37], accepting the existence
of linearity in the dataset [38, 39]. For the calculations the MAKESENS 1.0 software was employed
[40], whereas the spatial patterns were developed by using the Kriging’s technique [41].
Figure 2: Map of the Nestos River sub-basin in Greece, indicating also the positions of the rain gauged
stations.
Table 1
Meteorological stations
Code Site name Longitude Latitude Altitude Operating period Owner
(m)
CHR Chrysoupoli 24.60°E 40.93°N 60 1985-2017 (n=33) HNMS
KAV-A Kavala (Amygdaleonas) 24.38°E 40.93°N 60 1956-1984 (n=29) HNMS
KAV-C Kavala (city) 24.41°E 40.94°N 5 1986-2004 (n=19) HNMS
MES Mesochori 24.47°E 41.27°N 120 1963-2018 (n=56) DEH
PAP Papades 24.21°N 41.35°N 830 1963-1990 (n=28) DEH
PRA Prasinada 24.55°E 41.35°N 660 1962-2018 (n=57) DEH
SID Sidironero 24.23°E 41.37°N 570 1963-2018 (n=56) DEH
TEM Temenos 24.47°N 41.29°N 920 1963-1990 (n=28) DEH
XAN Xanthi 24.88°E 41.13°N 83 1955-2011 (n=57) HNMS
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3. Results and Discussion
The spatial distribution of the annual precipitation based on the meteorological data of seven stations
for the 1st climatic period (1955-1984) in comparison with the respective pattern for the 2nd climatic
period (1985-2018) derived from data by 6 meteorological stations are depicted in Figure 3. The pattern
for the 1st climatic period indicates that in Nestos basin, precipitation presents annual values varying
from 580.1 mm in KAV-A station to 1533.5mm in XAN. The values were lower at the upper and
altitudinal higher part of the sub-basin, whereas, at the Delta (lower part) the magnitudes were much
higher. For the 2nd climatic period, the spatial pattern differentiated. The mountainous areas, located
in its upper (northern) part of the basin, received more precipitation compared to the past, while the
lower (southern) part appears to have more dry conditions. This is very important, considering that the
priority habitats 3170* and 91E0*, that are hosted at the lower part of the basin, require high water
availability to be preserved. This precipitation variability and its change to more arid conditions in the
Delta will probably affect the vegetation distribution in the area and increase the vulnerability of the
priority habitats. Ιt appears that the habitat 3170* (temporary ponds) is no longer present at the western
lower part of the sub-basin. In a recent recording, we found only one new temporary pond at the eastern
part of the Delta and in an altitudinal higher location. This pattern indicates that the recent precipitation
distribution in the basin, in association with the operation of the dams in Thysavros and Platanovrisi
(located near the MES station), has changed the vegetation pattern especially for the high risk habitats
with increased water requirements.
Figure 3: Spatial pattern of the annual precipitation in Nestos sub-basin in N. Greece for the two
climatic periods (1955-1984 and 1985-2018). Black dots indicate the positions of the meteorological
stations used for the spatial interpolation.
It should be noted, however, that during the recent climatic period, precipitation has increased in
magnitude at the upper and altitudinal higher parts of the basin, indicating that the local vegetation will
face more favorable conditions for its development compared to the past. These results are in line with
the findings by Proutsos et al. [21], who also address issues for the viability of the habitats at the lower
eastern part of the Delta in Nestos.
Apart from the absolute magnitudes of precipitation, extremely important is to investigate its
changing rates during the two time periods. Proutsos et al. [21] analyzed data of the period 1956-2017
from five meteorological stations and identified a general increasing but highly variable trend in annual
precipitation for the basin, with changing rates varying from -9.29 mm/y in KAV stations to +5.9 mm/y
in SID, whereas the negative trends were detected at the lower part of the basin. In the present study,
the changing rates differ between the two climatic periods. During the 1st climatic period the
precipitation trends for most stations are not significant (Figure 4). However, at the eastern lower part
of the basin, XAN station presented positive and very strong (a= 0.001) trend, while at the altitudinal
higher and northern station SID a strong (a=0.05) negative trend was detected. Positive but not
significant trends were detected for two stations (MES and KAV-A), whereas PAP, TEM and PRA had
negative but also not significant trends. This pattern has changed during the 2nd climatic period when
all stations except KAV-C presented positive trends. Specifically, MES, SID and CHR stations had
459
increasing and significant (a=0.05) annual trends, whereas XAN presented also a positive but not
significant trend. The only station with decreasing precipitation was KAV-C. This trend is very strong
(a=0.001) indicating a rapidly changing climate to drier conditions in the southern coastal part of the
basin. In this period the climate in the mountainous part became more favorable for the development of
natural vegetation compared to the past, but at the lower part of the basin, vegetation deals with more
dry conditions, that is rapidly changing the recent years.
Figure 4: Spatial pattern of the annual precipitation trends in Nestos sub-basin (N. Greece) for the two
recent climatic periods (1955-1984 and 1985-2018). The triangles indicate the positions of the
meteorological stations with upward-facing for positive and downward-facing for negative trends.
Grey color indicated the not significant trends, whereas blue and red arrows show the positive and
negative significant trends, respectively.
4. Conclusions
The precipitation patterns in the Hellenic part of Nestos’ basin is characterized by high spatial and
temporal variability. The northern and mountainous basin parts receive increased precipitation
compared to the past and these rates are significantly increasing during the last climatic period. At the
lower (coastal) and southern part of the basin, where habitats of high ecological value are located,
precipitation appears to have decreased, while in the latest climatic period the decreasing rates, mainly
at the lower western part of the basin are more rapid and strong. The habitats in the Delta are highly
vulnerable and are expected to be highly affected by the climate variability in the future, due to the
diminished annual precipitation and the rapidly changing climate to more arid conditions. To further
investigate the possible impacts of the changing climate on the natural vegetation conservation in the
region, continuous climate monitoring is necessary. It is also needed to investigate the temperature and
evapotranspiration patterns in order to have more reliable conclusions. The operation of the dams should
also be evaluated. In future work, a drought assessment and an analysis of the changes in the seasonal
and monthly precipitation patterns are necessary to enhance our knowledge for the region, in terms of
the possible future risks for the highly sensitive and extremely important, for its ecological value,
natural ecosystem of Nestos.
5. Acknowledgements
This work is financially supported by the project “Bioclima and natural vegetation in Greece” funded
by the Hellenic Agricultural Organization “DEMETER”. The climate data for the stations of KAV-A,
KAV-C, CHR and XAN were kindly provided by the Hellenic National Meteorological Service
(HNMS).The authors also express their gratitude to the Public Power Corporation S.A. (DEH) and
especially to Mrs. Kreouza Mangina, Acting Head of Hydrology Sector of the Hydro-Electric Projects'
Engineering-Construction Department of DEH, for supporting this research by providing the climate
data for the MES, PAP, PRA, SID and TEM stations.
460
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