=Paper=
{{Paper
|id=Vol-3293/paper92
|storemode=property
|title=Decadal Variation of Aridity and Water Balance Attributes at the Urban and Peri-urban Environment of Attica-Greece
|pdfUrl=https://ceur-ws.org/Vol-3293/paper92.pdf
|volume=Vol-3293
|authors=Nikolaos D. Proutsos,Alexandra D. Solomou,Dimitris Tigkas
|dblpUrl=https://dblp.org/rec/conf/haicta/ProutsosST22
}}
==Decadal Variation of Aridity and Water Balance Attributes at the Urban and Peri-urban Environment of Attica-Greece==
https://ceur-ws.org/Vol-3293/paper92.pdf
Decadal Variation of Aridity and Water Balance Attributes at
the Urban and Peri-urban Environment of Attica-Greece
Nikolaos D. Proutsos 1, Alexandra D. Solomou 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, 9 Iroon Polytechneiou, 15780 Athens, Greece
Abstract
Aridity and changes of the water balance attributes can have a significant impact on the
vegetation patterns in both urban and rural environments. In this work, the decadal changes of
water budget related attributes (precipitation, potential evapotranspiration, water deficit and
surplus) are investigated in conjunction with indices used in climate classification as the
Thornthwaite's Aridity Index (AI), the potential evapotranspiration PET percentage of the drier
trimester to the PET of the decade (CEET), the ratio of the average annual decadal precipitation
to the average annual precipitation of the total timeseries (RPI) and the Moisture Index (MI) in
order to assess the climate variability patterns in an urban and a peri-urban site in the region of
Attica, central Greece. Result indicate major changes through the recent decades for most of
the examined parameters to more arid conditions with more limited water availability for the
vegetation, while these change are more rapid and severe in the urban areas.
Keywords 1
Climate, Aridity, Attica, Thornthwaite, UNEP
1. Introduction
Precipitation and soil water availability can highly affect plants growth rates and dynamics [1,2] due
to their impact in evapotranspiration rates. The urban infrastructures appears to play also a very
significant role in determining the urban climate [3-5]. The frequent and long lasting droughts [6], in
conjunction with the continuously changing climate in the Mediterranean and specifically in Greece [7-
11] underline the need for continuous monitoring of climate attributes in order to evaluate possible
current or future effects on natural or urban vegetation. This is critical considering that the
Mediterranean climate is characterized by rapid changes, relatively low water availability and increased
deficits especially during the periods that plants have high water requirements.
The purpose of this study is to investigate the changes of aridity and related parameters to the water
balance in an urban and a peri-urban site in Attica, which is a region of Greece that is highly affected
by urbanization within the last decades. The climate attributes were studied by using long term
meteorological data (1955-2019) on a decadal time-step, under the framework of the water balance
approach proposed by Thornthwaite [12] and revised by Thornthwaite and Mather [13, 14], which is
the base of UNEP's [15] aridity climate classification system that is widely used in climate research.
The present study may be considered as a useful for detecting possible future risks on a local lever and
for adopting measures for more sustainable urban design in Mediterranean cities.
Proceedings of HAICTA 2022, September 22–25, 2022, Athens, Greece
EMAIL: np@fria.gr (A. 1); solomou@fria.gr (A. 2); ditigas@mail.ntua.gr (A. 3)
ORCID: 0000-0002-8270-2991 (A. 1); 0000-0002-0014-1909 (A. 2); 0000-0002-2001-259X (A. 3)
©️ 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)
472
2. Study Area and Data
This work was implemented for the broader area of Attica. Long-term meteorological data obtained
from two stations located near the urban (N. Filadelphia) and the peri-urban (Tatoi) environments of
Attica were analyzed. More specifically, monthly precipitation data for the station of N. Filadelphia
(38o 03' N, 23o 40' E, alt. 12.0 m a.s.l.) were obtained by the station owned by the Hellenic National
Meteorological Service (HNMS) and cover the time period 1955-2010. The monthly average air
temperature data series for the same station were available for the period 1955-2018. For both time
series, the monthly gaps for the year 2019 (for air temperature) and years 2012-2019 (for precipitation)
were filled by the nearby operating station (38o 02' 00" N, 23o 42' 00" E, alt. 87 m a.s.l.) owned by the
National Observatory of Athens (NOA) (https://www.meteo.gr/).
To assess the peri-urban environment of Attica, data from the meteorological station of Tatoi were
used. The station is located at the downhill of Parnitha's mountainous forest, which has been declared
as a National Forest and is also protected as a Natura 2000 site. The station, owned by HNMS, is located
in 38o 06' Ν, 23o 47' Ε, alt. 236.0 m a.s.l. and has available monthly average air temperature and
precipitation data for the time period 1955-2017. The time-series of this station for the years 2018 and
2019 were obtained from the nearby operating station of NAO (38o 06' 00" N, 23o 48' 00" E, alt. 283 m
a.s.l.). From the above monthly data, the decadal time-series were produced for this work, as averages
of the time periods 1955-1959 (1950's), 1960-1969 (1960's), 1970-1979 (1970's), 1980-1989 (1980's),
1990-1999 (1990's), 2000-2009 (2000's) and 2010-2019 (2010's).
The decadal data were used to assess the aridity and the water balance in the two sites. Both aridity
and water balance related attributes (water surplus S and water deficit D) were estimated by
Thornthwaite's water balance approach [12-14], assuming that the soil water holding capacity is equal
to 300 mm for a soil depth of 150cm that is proposed for silt loam soils [16] and is generally accepted
for climate assessment in Greece [11, 17]. The potential evapotranspiration PET was estimated
according to Thornthwaite [12], whereas UNEP's [15] aridity index (AI) was applied for the climate
classification in different aridity classes: hyper-arid HA (AI<0.05), arid A (AI=0.05-0.20), semi-arid
SA (AI=0.20-0.50), sub-humid SH (AI=0.50-0.65) and humid H (SA>0.65). Climate subtypes were
also defined based on PET annual values:
• E' (glacial, PET<142 mm),
• D' (tundra, PET=142-285 mm),
• C'1 (microthermic, PET=285-427 mm),
• C'2 (microthermic, PET=427-570 mm),
• B'1 (mesothermic, PET=570-712 mm),
• B'2 (mesothermic, PET=712-855 mm),
• B'3 (mesothermic, PET=855-997 mm),
• B'4 (mesothermic, PET=997-1140 mm) and
• A' (megathermic, PET>1140 mm).
Moreover, the assessment was performed by the study of the Moisture Index (MI) described in
Thornthwaite and Mather [13] as the difference between humid (Ih=S/PET) and arid (Ia=D/PET) indices
that also define different climate sub-categories (A, B, C, D and E climatic types and d, r, s and w sub-
types). In addition, the potential evapotranspiration PET percentage of the drier trimester to the PET of
the decade CEET was also used for the classification to different climate sub-types:
• a' (CEET<0.480),
• b'4 (CEET=0.480-0.519),
• b'3 (CEET=0.519-0.563),
• b'2 (CEET=0.563-0.616),
• b'1 (CEET=0.616-0.680),
• c'2 (CEET=0.680-0.763),
• c'1 (CEET=0.763-0.880) and
• d' (CEET>0.880).
Finally, the changes of the ratio of the average annual decadal precipitation to the average annual
precipitation of the total time-series (RPI) for both sites, were also investigated.
473
3. Results and Discussion
Considering the total dataset for the period 1955-2019 the climate in both the urban affected site in
N. Filadelphia as well as the peri-urban site in Tatoi is semi-arid, mesothermal, with zero excess of
water and moderate concentration of thermal efficiency in summer (climate types: D B'3 d b'3 and D B'2
d b'3, respectively). This general climate classification is in line with the findings of previous climate
studies in Greece [11, 17], but it also shows important differences per decade as revealed by the decadal
climate analysis. The climate types per decade based on Thornthwaite and Mather [13] classification
are depicted in Table 1. The changes of the main water balance attributes in each site are different and
graphically depicted in Figure 1.
Table 1
Climate types based on Thornthwaite and Mather (1955) classification.
Tatoi N. Filadelphia
Decade
(peri-urban site) (urban site)
1950's D B'2 d b'3 D B'3 d b'3
1960's D B'2 d b'4 D B'3 d b'4
1970's D B'2 d b'4 D B'3 d b'3
1980's D B'2 d b'3 D B'3 d b'3
1990's D B'2 d b'3 D B'3 d b'3
2000's D B'3 d b'3 D B'3 d b'3
2010's D B'3 d b'3 D B'3 d b'3
1955-2019 D B'2 d b'3 D B'3 d b'3
1000 a. 1000 b.
990
982
976
935
908
906
891
Precipitation (mm/y)
880
873
800 800
852
845
844
833
819
PET (mm/y)
600 600
550
537
533
513
499
484
400 400
454
446
428
427
427
422
413
403
200 200
0 0
1950 1960 1970 1980 1990 2000 2010 1950 1960 1970 1980 1990 2000 2010
Decade Decade
1000 c. d.
800 S (mm)
Decade
Tatoi N. Filadelphia
D (mm/y)
600 1950 0 0
1960 10.28 0
542
539
525
1970
494
400 0 0
464
456
435
410
1980 0 0
358
346
338
330
324
1990
307
200 0 0
2000 0 0
2010 1.16 0
0
1950 1960 1970 1980 1990 2000 2010
Decade
Figure 1: Decadal (1950's to 2010's) values of precipitation P, potential evapotranspiration PET,
water deficit D, water surplus S for the sites of N. Philadelphia (red bars) and Tatoi (blue bars), based
on Thornthwaite's water balance approach.
474
Precipitation in N. Filadelphia presents minor decadal changes, ranging from 413mm (1950's) to
454mm (1960's), whereas in Tatoi varies from 403mm (1980's) to 550mm (2010's). The 1980's decade
for the Tatoi’s station is the driest highly affecting the water balance of the site, since it is associated
with moderate high PET (833mm). In general, at both sites the PET decadal values are high (varying
from 891 mm in 1950’s to 990 in 2000's for N. Filadelphia and from 819mm in 1970's to 880mm in
2010's for Tatoi) presented to increase the recent decades more rapidly in N. Filadelphia (trend slope
18.2 mm/decade) than in Tatoi (6.3mm/decade). These changes of PET in conjunction with the rather
stable precipitation result in increased water deficits D that vary from 435 mm in 1960's to 542mm in
2000's for N. Filadelphia, with an increasing trend of about the same magnitude as in PET
(17.7mm/decade). On the other hand, the less increasing rates of PET in Tatoi under the almost stable
precipitation regime (with the exception of 1980's) result rather stable D values. In addition, in both
sites the water excess (water surplus S) remains negligible or zero regardless of the decade. An
exception can be identified for the 1960's and 2010's in Tatoi, when minor S values were recorded
(10.28 and 1.16mm respectively) indicating a minor water surplus on an annual basis.
The impact of the above-mentioned changes and the relations between the water balance attributes
(Precipitation, PET, D and S) in the two sites, highly affect important indices used in climate
classification. The decadal values of the Thornthwaite's Aridity Index (AI), the potential
evapotranspiration PET percentage of the drier trimester to the PET of the decade (CEET), the ratio of
the average annual decadal precipitation to the average0.56annual precipitation of the total time-series
sub-humid (SH) zone
(RPI)0.60
and the Moisture
0.63 0.63Index (MI) for the sites
0.63of N. Filadelphia and Tatoi are presented in Figure 2.
0.61
0.59 0.55
0.56
Index AI
sub-humid (SH) zone
0.48 0.57
0.60 0.50
0.63 0.63
0.50 0.61 0.63 0.54
0.59 0.55
CEETCEET
Index AI
0.46 0.50 0.47 0.48 0.57
0.45 0.44 0.45
AridityAridity
0.50
0.40 0.43 0.53
0.54
0.46 0.47 semi-arid (SA) zone
0.40
0.30
0.45 0.44 0.43 0.45
0.52
0.53
semi-arid (SA) zonea. b.
0.30
0.20 0.51
0.52
1950 1960 1970 1980 1990 2000 2010 1950 1960 1970 1980 1990 2000 b.2010
a.
0.20 Decade 0.51 Decade
1950 1960 1970 1980 1990 2000 2010 1950 1960 1970 1980 1990 2000 2010
Decade Decade
Decade
1950 1960 1970 1980 1990 2000 2010
-0.30 Decade
1.10
1950 1960 1970 1980 1990 2000 2010
1.05 -0.35
-0.30
1.10
1.00 -0.40
1.05 -0.35
RPI RPI
0.95
MI
1.00 -0.45
-0.40
0.90
0.95 -0.50
MI
0.85 -0.45
0.90
0.80 c.
-0.55
-0.50
0.85 d.
0.75 -0.60
0.801950 1960 1970 1980 1990 2000 c.2010 -0.55
Decade d.
0.75
Figure 2: Graphical representation of the average -0.60
1950 1960 decadal (1950s to 2010s) values of a) the
1970 1980 1990 2000 2010
Thornthwaite’s Aridity Index (AI), b) the potential evapotranspiration PET percentage of the drier
Decade
trimester to the PET of the decade (CEET), c) the ratio of the average annual decadal precipitation to
the average annual precipitation of the total time-series (RPI) and d) the Moisture Index (MI) for the
sites of N. Filadelphia (red lines) and Tatoi (blue line).
475
The combined effect of Precipitation and PET is incorporated in the values of AI. Its decadal values
(varying between 0.43 in 2000's and 0.50 in 1960's) confirm the more arid conditions prevailing in the
urban site of N. Filadelphia, which has a semi-arid (SA) climate, according to UNEP's [15] climate
aridity classification compared to the semi-humid (SH) climate in the peri-urban site of Tatoi (AI range
from 0.48 in 1980's to 063 in 1960's, 1970's and 2010's). However, it is worth noting that the climate in
N. Filadelphia became more arid during the recent decades compared to the past with a persisting stable
trend for the AI values. This is in line with similar studies in urban and forest environments in Greece
that increasing aridity trends were also identified [4, 5, 7-11]. On the contrary, the sub-humid conditions
in Tatoi are rather stable with time, with the exception of the 1980's decade, when the climate became
semi-arid due to the diminished precipitation. For the specific decade the RPI values are reduced (0.79)
indicating that in 1980's precipitation was by 21% lower than the long-term climatic average.
The CEET values indicate that the cumulative PET in summer is more than 50% of the annual total,
indicating that the highest evapotranspiration rates and thus available water demands are recorded for
summer. This fact introduces the need for irrigation support, especially in the urban environment, in
order to sustain vegetation, considering also that summer precipitation consists on average only 7.7%
in N. Filadelphia and 8.4% in Tatoi of their total annual precipitation.
4. Conclusions
The above patterns indicates that the region of Attica generally has small water inputs from
precipitation that are mainly consumed for evapotranspiration, allowing almost zero surpluses. On the
contrary, the water deficits are high with increasing trends in the recent decades compared to the past.
The urban environment appears to face even more reduced water availability with less precipitation and
higher evapotranspiration rates, compared to the peri-urban environment, resulting in higher water
deficits with serious negative impacts on the urban green infrastructures in terms of plants’ water
requirements and their heat and water tolerance. This pattern is becoming even more hostile the recent
decades compared to the past, whereas its changes are more rapid in the urban environment compared
to the peri-urban.
5. Acknowledgements
The climate data used in this work were kindly provided by the Hellenic National Meteorological
Service (HNMS) and the National Observatory of Athens (NOA, https://www.meteo.gr/). This work
was financially supported by the LIFE17 GIC/GR/000029 GrIn project "Promoting Urban Integration
of Green INfrastructure to improve climate governance in cities", which is co-funded by the European
Commission under the "Climate Change Action-Climate Change Governance and Information"
component of the LIFE Programme.
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