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Czech University of Life Sciences Prague, Faculty of Agrobiology, Food and Natural Resources, Department of Agroecology and Biometeorology, Prague, Czech Republic [email protected]
International Scientific Conference
9 - 11 September 2013 | Skalica, Slovakia
Abstract
This study presents a detailed assessment on drought characteristics in a multi-scalar way based on the Standardized Precipitation
Evapotranspiration (SPEI) in the Republic of Moldova.
This study combined two SPEI datasets: (1) the global 0.5°gridded the SPEI dataset at time scales between 1 and 48 months from
December 1950 to May 2013 over Moldova domain (45.01ºN-49.01ºN; 26.52ºE-30.48ºE) obtained from the SPEIbase, and (2) the
Chisinau climatological station as a representative station with relatively long continuous series (1945-2011) in the Republic of
Moldova.
The SPEIbase is based on the FAO-56 Penman-Monteith estimation of potential evapotranspiration from CRU with spatial
resolution of 0.5ºlat x 0.5ºlon.
The SPEI at climatological station is based on Hargreaves estimation of potential evapotranspiration (the minimum and maximum
air temperatures and extraterrestrial radiation).
The 0.5°gridded SPEIbase as new global product can be suitable for the detection, monitoring, and assessment of drought conditions
at the regional scale.
Key words: SPEIbase, time-scale, summer and winter drought
Acknowledgements:
This study was supported by project 6046070901.
References:
Beguería, S., Vicente-Serrano, S.M. & Angulo, M., 2010: A multi-scalar global drought data set: the SPEIbase: a new gridded product for the analysis of drought variability and impacts. Bulletin of the American Meteorological Society 91: 1351-1354
Vicente-Serrano, S.M., Beguería, S., López-Moreno, J.I. (2010): A Multi-scalar drought index sensitive to global warming: The Standardized Precipitation Evapotranspiration Index – SPEI. Journal of Climate 23 (7): 1696-1718.
Vicente-Serrano, S.M., Beguería, S., Eklundh, L., Gimeno, G., Weston, D., Kenawy, A.E., López-Moreno, J.I., Nieto, R., Ayenew, T., Konte, D., Ardö, J., Pegram, G.G.S. (2012): Challenges for drought mitigation in Africa: The potential use of geospatial data
and drought information systems. Applied Geography 34: 471-486.
Latitude (°N)
Longitude (°E)
°C
t2m JJA - Stations
45
45.5
46
46.5
47
47.5
48
48.5
49
26.5 27.5 28.5 29.5 30.5
20.0
19.519.0
18.5
19.5
20.5
20.0
20.5
Latitude (°N)
Longitude (°E)
mm
26.5 27.5 28.5 29.5 30.545
45.5
46
46.5
47
47.5
48
48.5
49
185
200
tpr mm JJA - Stations
220
175
200
225
Box 1. Summer temperature mean and precipitation total climatologies (1960-1997) and drought characteristics (1945-2011) in the Republic of Moldova.
Summer (JJA)
The summer mean of air temperature in Republic of Moldova was calculated
from monthly data from 15 meteorological stations for the period 1961-
1997.
The summer mean air temperature ranges between +18.5ºC and +21.0ºC
(map A).
The hottest summer: 2007 with Tmean ranging 22.0 to 25.0ºC (exceeding
the norm with 3.0-4.0ºC)
Absolut maximum: +41.5ºC (on 21 July 2007 in Kamenka, source
Moldova’s State Hydrometeorological Service source)
Precipitation: in average 175-235 mm (map B )
The lowest: 37 mm (Cahul, 1924)
The hierarchy of the driest summers according to the SPEI: 2007, 1946,
1951, 1968, 2000, 1953, 1951, 1945, 2003 and 2009.
The longest dry periods: 1945-1947, 1950-1951 and 1999-2000.
Winter (DJF)
The winter mean of air temperature in the Republic of Moldova was calculated
from monthly data from 15 meteorological stations for the period 1960-1997.
The winter air temperature mean ranges between -1.4 and -3.4ºC (map A).
The coldest winter: 1953/1954, with Tmean ranging -8.0 to -9.0ºC (6.0-7.0ºC
lower than the norm according to Moldova’s State Hydrometeorological
Service).
The warmest winter: 2006/2007, with Tmean ranging +1.0ºC to
+3.0ºC (exceeded the norm with 4.0-5.0ºC).
The high variability of the air temperature during winter season is one of the
climatic particularities of Moldova.
Precipitation: on average 87-117 mm or 16-20% of the average annual amount
(map B).
The hierarchy of the driest winters according to the SPEI: 1948, 1949, 2006,
1953, 1990, 1949, 2002, 1990, 2007, 1946, 1994 and 1959.
The longest dry periods: 1948-1954, 1958-1959, 1977-1978, 1989-1990, 2001-
2002 and 2006-2007.
Latitude (°N)
Longitude (°E)
°C
26.5 27.5 28.5 29.5 30.545
45.5
46
46.5
47
47.5
48
48.5
49
-2.5
-2.0
t2m DJF - Stations
-1.5
-3.4
-3
-2.6
-2.2
-1.8
-1.4
-3.0
Latitude (°N)
Longitude (°E)
mm
26.5 27.5 28.5 29.5 30.545
45.5
46
46.5
47
47.5
48
48.5
49
105
115
tpr mm DJF - Stations
87
97
107
117
Box 2. Winter temperature mean and precipitation total climatologies (1960-1997) and drought characteristics (1945-2011) in the Republic of Moldova.
Data and methods
This study presents the evolution of two SPEI datasets:
(1) the global 0.5°gridded the SPEI dataset at time scales between 1 and 48
months from December 1950 to May 2013 over Moldova domain (45.01ºN-49.01ºN;
26.52ºE-30.48ºE) obtained from the SPEIbase (Beguería et al., 2010);
(2) the Chisinau climatological station as a representative station with
relatively long continuous series (1945-2011) in the Republic of Moldova.
The SPEIbase is based on the FAO-56 Penman-Monteith estimation of potential
evapotranspiration from CRU with spatial resolution of 0.5ºlat x 0.5ºlon. A
complete description of the data and links to download the files, are provided at
http://sac.csic.es/spei.
In this study, gridded data of SPEIbase have been downloaded to climatological
station coordinates (Figure 1). The SPEI series at Chisinau station was calculated
as follows:
the parameterization of potential evapotranspiration (PET) based on
monthly minimum (Tmin) and maximum air temperature (Tmax) and
extraterrestrial radiation;
a simple monthly water balance (D), calculated as the difference between
monthly precipitation (P) and potential evapotranspiration (PET) and
normalisation of the water balance into a log-logistic probability
distribution to obtain the SPEI series at time scales between 1 and 24
months.
In this study, we have also analysed the trends of extreme temperatures (Tmin and
Tmax) and precipitation anomalies as helpful factors to assess their influence on
drought characteristics.
Table 1 The 7 classes of the SPEI category according to its values
Results and discussion
The high variability of temperature and precipitation during the 1950s and 2000s is associated with multiple periods of large drought extent. The majority of the hottest and driest summers since 1945 were precedes
by winter and spring precipitation deficit over Moldova (e.g. 1946, 1953, 2000 and 2007 ) (Boxes 1-2) .
For all the time scales of the SPEI calculation during the warm season of the year (April to September), the longest duration and highest severity was identified during in the mid 1940s-1950s, 1960s and 2000s
(Box 3). These periods correspond to the association of the highest temperature and lowest precipitation anomalies (i.e., more than 2.5°C associated with precipitation anomalies up to 60% below normal) (Box 3).
The largest impact on water deficit during the last three decades was found to be mainly due to the increase of maximum temperature (+0.7°C decade-1) and minimum temperature (+0.5°C decade-1) associated with
decreased precipitation (20 mm decade-1).
The increasing trend of extreme temperatures in the Republic of Moldova has particularly affected Tmin (the highest positive deviation was ranging between 1.5°C to 3.5°C) during warm season of the year and the
increasing water deficit in this season (top panel of Box 3).
Hovmoller-type diagram provides a visualisation of the spatiotemporal evolution of the 0.5°gridded the SPEIbase series at time scales between 1 and 48 months for the period 1950-2013 over Moldova domain
(bottom panel of Box 3).
Conclusion
Two SPEI data sets and two different method of parametrization of potential evapotranspiration were used to compare ability of gridded SPEIbase to reproduce the spatial and temporal evolution of drought at
the territory of the Republic of Moldova.
The approach to drought characterisation based on the global 0.5°gridded SPEIbase calculated for various accumulation periods provides comprehensive results on the complexity of drought phenomena in the
Republic of Moldova.
(A)
(B)
(B)
(A)
Standardized Precipitation Evapotranspiration (SPEI)
The SPEI is a site-specific drought indicator of deviations from the average water
balance (precipitation minus potential evapotranspiration) (Vicente-Serrano et al.,
2010). The standardization procedure for SPEI follows the same steps as SPI, however the
developers of SPEI recommend using the three parameter log-logistic theoretical
distribution to account for common negative values which are found in the time
series (precipitation – PET).
One of the weaknesses of the SPEI is that it requires more data than the SPI. Like the
SPI, the SPEI has trouble dealing with arid climates where precipitation is near zero
(Vicente-Serrano et al., 2012). However, the SPEI includes the role of temperature on drought severity by means of
its influence on the atmospheric evaporation demand.
SPEI Drought
category
Probability
≥2.0 Extreme wet 0.02
1.50 – 1.99 Severe wet 0.06
1.49 - 1.00 Moderate wet 0.10
0.99 - -0.99 Normal 0.65
-1.00 – -1.49 Moderate drought 0.10
-1.50 - -1.99 Severe drought 0.05
≤-2.00 Extreme drought 0.02
198019601950 1970 1990 2010
4
8
16
12
20
24
SPE
I at
tim
e-sc
ales
extreme
drought
severe
droughtmoderate
drought normal
moderate
wetsevere
wet
extreme
wet
Chisinau - 46°58'03''N, 28°51'23''E h= 173 m a.s.l.
2000
-3
-2
-1
0
1
2
3
19
45
19
48
19
52
19
56
19
59
19
63
19
67
19
70
19
74
19
78
19
81
19
85
19
89
19
92
19
96
20
00
20
03
20
07
20
11
SPEI-3 (winter)
-3
-2
-1
0
1
2
3
19
45
19
48
19
52
19
56
19
59
19
63
19
67
19
70
19
74
19
78
19
81
19
85
19
89
19
92
19
96
20
00
20
03
20
07
20
11
SPEI-3 (summer)
Evolution of the SPEI at 3-month
lag during winter (DJF) from
December of 1946 to February of
2011 at Chisinau climatological
station
Evolution of the SPEI at 3-month lag
during summer (JJA) from June of
1945 to August of 2011 at Chisinau
climatological station
According to SPEI-6 values and its categories (Table 1) the drought of May 1986 based on station observations was characterized as severe in most of the regions and extreme in the eastern half of country.
Based on the global 0.5°gridded SPEIbase , the drought was severe and extreme, but the area with extreme drought is larger than that resulted from 15 station observations.
Similarly, for August 1986 based on station observation the drought was severe and extreme over the whole country, moderate in the southern half, severe and extreme in the northern half of the country based
on the global 0.5°gridded SPEIbase .
However, the global 0.5°gridded SPEIbase dataset capture the general characteristics of drought in terms of spatial and temporal distribution and it can be used for vulnerability to drought assessments for the
Republic of Moldova
Box 4. Spatial evolution of SPEI at 6-month accumulation period during the driest growing season of 1986 over Moldova domain at 0.5°gridded SPEIbase (top) and stations dataset (down).
-3
-2
-1
0
1
2
3
4
5
194
5
195
0
195
5
196
0
196
5
197
0
197
5
198
0
198
5
199
0
199
5
200
0
200
5
201
0
Te
mp
era
ture
An
om
aly
(
C)
t° C tmax smooth (a)
-2
-1
0
1
2
3
4
194
5
195
0
195
5
196
0
196
5
197
0
197
5
198
0
198
5
199
0
199
5
200
0
200
5
201
0
Te
mp
era
ture
An
om
aly
(
C)
t° C tmin smooth (b)
-300
-200
-100
0
100
200
300
194
5
195
0
195
5
196
0
196
5
197
0
197
5
198
0
198
5
199
0
199
5
200
0
200
5
201
0Pre
cip
ita
tio
n A
no
ma
ly (
mm
)
mm mm smooth(c)
Box 3. Temporal evolution of data series from 1945 to 2011: upper panel) air
anomalies of maximum temperature (a) and minimum temperature (b), and precipitation
totals (c) during the warm season of the year (c). middle panel) SPEI at time scales
from 1 to 24 months and the SPEI at 12-month lag, and bottom panel) spatiotemporal
evolution of the 0.5°gridded the SPEIbase series at time scales between 1 and 48 months
for the period 1950-2013 over Moldova domain (45.01ºN-49.01ºN; 26.52ºE-30.48ºE).
Figure 1.
Location of the 15 meteorological stations and their
elevation (m a.s.l.) situated in the Republic of Moldova.
1950 1960 1970 1980 1990 2000 2010
5
10
15
20
25
30
35
40
extreme
wet
severe
wetmoderate
wetnormalmoderate
drought
severe
drought extreme
drought
Moldova domain - 45.01°N - 49.01°N, 26.52°E - 38.48°E
SPEI
at ti
me-s
cales
48
SPEIbase from January 1950 to May 2013
26.5 27 27.5 28 28.5 29 29.5 30 30.545
45.5
46
46.5
47
47.5
48
48.5
Longitude (°E)
Latitude (°N)
May 1986 - SPIEbase-6
normalmoderate
wet
severe
wet
extreme
wetmoderate
drought
severe
drought
extreme
drought
Longitude (°E)
Latitude (°N)
June 1986 - SPEIbase-6
normalmoderate
wet
severe
wet
extreme
wetmoderate
drought
severe
drought
extreme
drought
26.5 27 27.5 28 28.5 29 29.5 30 30.545
45.5
46
46.5
47
47.5
48
48.5
Longitude (°E)
Latitude (°N)
July 1986 - SPEIbase-6
normalmoderate
wet
severe
wet
extreme
wetmoderate
drought
severe
drought
extreme
drought
26.5 27 27.5 28 28.5 29 29.5 30 30.545
45.5
46
46.5
47
47.5
48
48.5
Longitude (°E)
Latitude (°N)
August 1986 - SPEIbase-6
normalmoderate
wet
severe
wet
extreme
wetmoderate
drought
severe
drought
extreme
drought
26.5 27 27.5 28 28.5 29 29.5 30 30.545
45.5
46
46.5
47
47.5
48
48.5
Longitude (°E)
Latitude (°N)
May 1986 - SPEI-6 by stations
normalmoderate
wet
severe
wet
extreme
wetmoderate
drought
severe
drought
extreme
drought
26.5 27 27.5 28 28.5 29 29.5 30 30.545
45.5
46
46.5
47
47.5
48
48.5
Longitude (°E)
Latitude (°N)
June 1986 - SPEI-6 by stations
normalmoderate
wet
severe
wet
extreme
wetmoderate
drought
severe
drought
extreme
drought
26.5 27 27.5 28 28.5 29 29.5 30 30.545
45.5
46
46.5
47
47.5
48
48.5
Longitude (°E)
Latitude (°N)
August 1986 - SPEI-6 by stations
normalmoderate
wet
severe
wet
extreme
wetmoderate
drought
severe
drought
extreme
drought
26.5 27 27.5 28 28.5 29 29.5 30 30.545
45.5
46
46.5
47
47.5
48
48.5
Longitude (°E)
Latitude (°N)
July 1986 - SPI06 by stations
normalmoderate
wet
severe
wet
extreme
wetmoderate
drought
severe
drought
extreme
drought
26.5 27 27.5 28 28.5 29 29.5 30 30.545
45.5
46
46.5
47
47.5
48
48.5
July 1986 – SPEI-6 by stations
