=Paper=
{{Paper
|id=Vol-3293/paper85
|storemode=property
|title=Drought Assessment in Nestos River Basin (N. Greece) for the Period 1955-2018
|pdfUrl=https://ceur-ws.org/Vol-3293/paper85.pdf
|volume=Vol-3293
|authors=Nikolaos D. Proutsos,Dimitris Tigkas,Irida Tsevreni,Magdalini Tsevreni
|dblpUrl=https://dblp.org/rec/conf/haicta/ProutsosTTT22
}}
==Drought Assessment in Nestos River Basin (N. Greece) for the Period 1955-2018==
https://ceur-ws.org/Vol-3293/paper85.pdf
Drought Assessment in Nestos River Basin (N. Greece) for the
Period 1955-2018
Nikolaos D. Proutsos 1, Dimitris Tigkas 2, Irida Tsevreni 3 and Magdalini Tsevreni 4
1
Hellenic Agricultural Organization “DEMETER”, Institute of Mediterranean Forest Ecosystems, Terma
Alkmanos, 11528 Athens, 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, 9 Iroon Polytechneiou, 15780 Athens, Greece
3
Department of Early Childhood Education, University of Thessaly, Volos, Greece
4
National Centre for Social Research, 9 Kratinou & Athinas st., 105 52 Athens, Greece
Abstract
Drought is a significant meteorological phenomenon that can seriously impact natural
ecosystems. Drought assessment and monitoring should be continuous in regions of high
ecological importance, for the conservation of natural vegetation distribution and dynamics. In
this study, we analyzed monthly precipitation data obtained from five meteorological stations
in the Nestos’ river sub-basin in Greece in order to detect drought episodes during the period
1955-2018 by employing the Standardized Precipitation Index (SPI). The results indicate that
the coastal and altitudinal lower areas of the region faced more frequent and more severe
drought events during the recent years compared to the past, whereas the climatic conditions
in the mountainous areas are more favorable. The hydrological years 1977-1978, 1984-1985,
1988-1989, 1998-1999 and 1999-2000 were the years of the most severe droughts in the basin.
From the trend analysis of the SPI it appears that the lower part of the sub-basin is anticipated
to face even more droughts in the future. These patterns may have significant impacts on the
natural rainfed vegetation, especially at the river’s Delta where habitat types of high priority
are located. Thus, the need to adopt measures for the conservation of the local ecosystem is
critical, considering also that the local habitat types are characterized by high demands for
water availability.
Keywords 1
SPI, drought, Nestos, Mesta, trends, Mann-Kendall, Sen slope, DrinC software
1. Introduction
The Mediterranean basin includes diverse types of habitats and it is considered a biodiversity hotspot
[1,2], due to the combination of climate conditions and the variety of geographical and topographical
features of the region. Climate shifts and extreme events, such as droughts, in this area may lead to
alterations of the ecological balance and cause pressures to human activities. Many studies have
identified trends, especially in precipitation timeseries [3-9], as well as in drought patterns [10-13],
indicating a tendency to drier conditions [14,15] in various areas within the Mediterranean region. The
efficient management of drought risks is essential for compensating the impacts of droughts on several
sectors, including the economy, the societies and the environment. To this end, proper understanding,
identification and monitoring of drought characteristics is essential, especially in economically and
ecologically important and vulnerable regions. Additionally, year to year drought conditions is critical
Proceedings of HAICTA 2022, September 22–25, 2022, Athens, Greece
EMAIL: np@fria.gr (A. 1); ditigas@mail.ntua.gr (A. 2); itsevreni@uth.gr (A. 3); mtsevreni@ekke.gr (A. 4)
ORCID: 0000-0002-8270-2991 (A. 1); 0000-0002-2001-259X (A. 2); 0000-0001-8065-1249 (A. 3); 0000-0002-2945-2014 (A. 4)
©️ 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)
429
to be monitored for assessing the effects on the sustainability of the natural rainfed ecosystems [16], as
decreased precipitation and droughts have a strong impact on plants’ growth dynamics [17,18].
Nestos is a transboundary river, shared between Bulgaria and Greece. The river delta, which is
located in the Greek sub-basin, is considered as of high ecological significance. Many parts of the basin,
including Nestos’ Delta, have been declared as Natura 2000 protected sites. Especially the river’s Delta
hosts a variety of priority habitats that require high water availability in order to be sustainable.
Therefore, drought monitoring is crucial in this region, considering also that the hydrological regime of
Nestos river is rather sensitive to drought episodes [19]. Furthermore, drought analyses using proper
tools, such as drought indices, is important for indicating appropriate management measures in
transboundary rivers [20].
The present study is based on previous studies by Proutsos et al. [21,22] that analyzed the
precipitation trends in the Greek part of Nestos river and assessed the changes occurred since the 1950s.
In this work, the drought conditions of this region are evaluated, analyzing the annual changes of the
SPI drought index and assessing the spatial variability in the basin.
2. Study Site and Climatic Data
The geophysical pattern of the study area, which includes the Greek sub-basin of Nestos river, is
presented in Figure 1. Details about the characteristics and information concerning the high ecological
importance of the area can be found in Proutsos et al. [21-23].
Figure 1: Geophysical map of the Nestos’ sub-basin (Greece) along with the positions of the five long-
operating meteorological stations.
The climate of the area is humid [15,24] according to UNEP’s [25] aridity classification system
based on Thornthwaite’s [26] water balance approach, whereas the recent precipitation trends [21,22]
indicate significant reduction in the coastal areas of the region, but also precipitation increase in the
mountainous part of the basin with high seasonal variability [21]. The changing trends are more rapid
at the current climatic period [22].
In this work, we assessed the drought conditions for the Greek part of the basin. Monthly
precipitation data series, obtained from five long-operating meteorological stations, were analyzed for
the period 1955-2018, on a hydrological year basis. The specific characteristics of the meteorological
430
stations are presented in Table 1. The drought assessment was performed by employing the widely used
Standardized Precipitation Index (SPI) [27], using DrinC software [28, 29]. The index is based solely
on precipitation data and can be applied for several timesteps. In this study, the annual timestep of the
hydrological year (October to September) was adopted, an approach that is considered suitable for
assessing drought impacts on water availability [30,31]. SPI values classify the adopted time period of
each year to one of the following eight classes (four wet and four dry): extreme drought (SPI≤-2.0),
severe drought (-2.02.0).
Table 1
Meteorological stations’ characteristics
Code Site name Longitude Latitude Altitude Operating period Owner
KAV Kavala 24.41°E 40.94°N 5m 1986-2004 (n=19) HNMS
MES Mesochori 24.47°E 41.27°N 120 m 1963-2018 (n=56) DEH
PRA Prasinada 24.55°E 41.35°N 660 m 1962-2018 (n=57) DEH
SID Sidironero 24.23°E 41.37°N 570 m 1963-2018 (n=56) DEH
XAN Xanthi 24.88°E 41.13°N 83 m 1955-2011 (n=57) HNMS
To detect possible trends of the annual SPI, the Mann-Kendall test was applied [32,33] and the trend
slopes were estimated by the Sen’s slope method [34]. These methods are widely used and are
considered reliable in hydrological and climatic trend analysis [6,21,35-37]. For the trend detections,
the evaluation of their significance and the calculation of their magnitudes, the MAKESENS 1.0
software was applied [38]. The spatial patterns presented in this work were developed by the application
of the Kriging’s interpolation technique, where the unknown SPI slope values at all points across a
defined spatial domain are estimated using a weighted average of all known values around the point
[39].
3. Results and Discussion
The annual values of the SPI, based on the precipitation data of the five meteorological stations, are
presented in Figure 2. The annual SPIs clearly indicate that the altitudinal lower coastal areas (KAV
and XAN stations) of the region, located at the lower part of the basin, experience more intense and
more frequent extreme or severe drought events during the recent years (after 1990). On the contrary,
at the altitudinal higher positions (MES and PRA stations) the drought events were more frequent and
intense in the previous decade (1980s), whereas at the mountainous areas (SID station) no extreme
droughts were detected.
More specifically, for KAV station, 1998-1999 and 2003-2004 were hydrological years of extreme
drought, 1996-1997 and 2001-2002 years of severe drought and 1994-1995, 1995-1996, 1997-1998,
2000-2001 and 2002-2003 years of moderate drought. The most severe drought in KAV occurred in
1998-1999, when SPI was -2.2.
XAN faced no extreme drought events, however 1998-1999, 1999-2000 and 2001-2002 were years
of severe droughts. The most severe drought year was 1999-2000 (SPI=-1.8).
In MES and PRA, 1984-1985 and 1988-1989 were extreme drought years. Severe droughts were
recorded in 1973-1974 and 1992-1993 and moderate droughts in 1989-1990, 1993-1994 and 2016-2017
for PRA station. Also, moderate drought was identified during the years 1967-1968, 1986-1987, 1989-
1990, 1991-1992, 1992-1993, 1993-1994 and 2000-2001 for MES station. The most extreme drought
years were 1988-1989 for MES (SPI=-2.3) and 1984-1985 for PRA (SPI=-2.5).
For SID station, no extreme droughts were identified. However, 1977-1978, 1980-1981 and 1992-
1993 were years of severe drought and 1975-1976, 1976-1977, 1984-1985 and 1991-1992, were years
of moderate drought. With regard to the available data, 1977-1978 was the year with the most stressful
conditions (SPI=-1.7).
Considering the years with the highest negative values in each station, i.e. 1998-1999 for KAV,
431
0.0
1.0
3.0
0.0
1.0
3.0
0.0
1.0
2.0
0.0
1.0
3.0
-3.0
-1.0
2.0
-3.0
-1.0
2.0
-3.0
-2.0
3.0
-3.0
-1.0
2.0
-2.0
-2.0
-1.0
-2.0
-3.0
-2.0
0.0
1.0
2.0
3.0
-1.0
1955-1956 1955-1956 1955-1956 1955-1956 1955-1956
1957-1958 1957-1958 1957-1958 1957-1958 1957-1958
1959-1960 1959-1960 1959-1960 1959-1960 1959-1960
1961-1962 1961-1962 1961-1962 1961-1962 1961-1962
1963-1964 1963-1964 1963-1964 1963-1964 1963-1964
1965-1966 1965-1966 1965-1966 1965-1966 1965-1966
Nestos’ river sub-basin.
1967-1968 1967-1968 1967-1968 1967-1968 1967-1968
1969-1970 1969-1970 1969-1970 1969-1970 1969-1970
1971-1972 1971-1972 1971-1972 1971-1972 1971-1972
1973-1974 1973-1974 1973-1974 1973-1974 1973-1974
1975-1976 1975-1976 1975-1976 1975-1976 1975-1976
1977-1978 1977-1978 1977-1978 1977-1978 1977-1978
1979-1980 1979-1980 1979-1980 1979-1980 1979-1980
1981-1982 1981-1982 1981-1982 1981-1982 1981-1982
1983-1984 1983-1984 1983-1984 1983-1984 1983-1984
1985-1986 1985-1986 1985-1986 1985-1986 1985-1986
432
1987-1988 1987-1988 1987-1988 1987-1988 1987-1988
1989-1990 1989-1990 1989-1990 1989-1990 1989-1990
1991-1992 1991-1992 1991-1992 1991-1992 1991-1992
1993-1994 1993-1994 1993-1994 1993-1994 1993-1994
severe drought events in the past, but not during the recent years.
1995-1996 1995-1996 1995-1996 1995-1996 1995-1996
1997-1998 1997-1998 1997-1998 1997-1998 1997-1998
12-month SPI (Oct-Sep): SID
12-month SPI (Oct-Sep): KAV
12-month SPI (Oct-Sep): PRA
12-month SPI (Oct-Sep): MES
1999-2000 1999-2000 1999-2000 1999-2000
12-month SPI (Oct-Sep): XAN
1999-2000
2001-2002 2001-2002 2001-2002 2001-2002 2001-2002
2003-2004 2003-2004 2003-2004 2003-2004 2003-2004
2005-2006 2005-2006 2005-2006 2005-2006 2005-2006
2007-2008 2007-2008 2007-2008 2007-2008 2007-2008
2009-2010 2009-2010 2009-2010 2009-2010 2009-2010
2011-2012 2011-2012 2011-2012 2011-2012 2011-2012
2013-2014 2013-2014 2013-2014 2013-2014 2013-2014
Mild drought
Severe drought
2015-2016 2015-2016 2015-2016 2015-2016 2015-2016
Extreme drought
Moderate drought
2017-2018 2017-2018 2017-2018 2017-2018 2017-2018
1999-2000 for XAN, 1988-1989 for MES, 1984-1985 for PRA and 1977-1978 for SID, the spatial
the basin faced drier conditions compared to the past, whereas the mountainous regions faced more
patterns of Figure 3 were produced. These patterns confirm that in the recent years the coastal areas of
Figure 2: Annual values of the SPI index for the operating period of the five meteorological stations in
Figure 3: Spatial distribution of the SPI for specific years with most extreme drought events, identified
by the available data from the five meteorological stations.
The trend analysis of the SPI values produced the pattern depicted in Figure 4, which indicates that
SPI presents negative and strong decreasing trends in the low altitude coastal areas, whereas at the
mountainous areas of the basin the conditions are more wet, however these latest positive trends are not
significant. These changes are anticipated to cause problem to the local high priority habitats that are
located at the lower part of the basin, since they are highly vulnerable in the changes of precipitation.
Such high water demanding ecosystems, are considered of high risk and require interventions to ensure
that they have the necessary water quantities in order to be sustained.
433
Figure 4: Changing trends of the SPI index with time. Q, is the changing rate of the index in y-1,
whereas the direction of the white triangles in each station indicates if the trend is either positive or
negative but in all cases the trend is not significant at a=0.10. The red triangle indicate negative and
strong trend at a=0.001.
4. Conclusions
In this work, a drought assessment was performed for the Nestos’ river sub-basin in N. Greece. The
region hosts a variety of significant habitats that require high water availability in order to be preserved.
The precipitation changes can highly affect the vegetation patterns in the region, thus the continuous
monitoring of drought is necessary. From the results of this study, it is indicated that the altitudinal
lower coastal part of the basin is at high risk and faces, in the recent years, more severe and frequent
drought events compared to the past. The western coastal areas are even more vulnerable. On the other
hand, the climatic conditions appear to be more favorable nowadays, compared to the past, in terms of
drought frequency and severity. This is expected to favor the existing mountainous ecosystems.
However, specific measures should be undertaken to conserve the highly valuable coastal ecosystem
and conserve the priority habits of the coastal zone. Such interventions should be assisted by the
operation of the existing uphill dams and impose the continuous co-operation of the stakeholders from
Greece and Bulgaria and the implementation of common strategies in order to achieve the ecological
goals.
5. Acknowledgements
This work is financially supported by the project “Bioclima and natural vegetation in Greece” which
is financed by the Hellenic Agricultural Organization “DEMETER”. The climate data for the KAV and
XAN stations 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 MES,
PRA and SID stations.
434
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