Klementová, E., Litschmann, T., Rožnovský, J: Assessment of Drought in Landscape. In: Participation of women in the fields of meteorology, operational hydrology and related sciences. Bratislava, 16-17. V. 2002, s. 143 - 148
Eva Klementová, Tomáš Litschmann ,
Jaroslav Rožnovský
Abstract:
In the article is shown the procedure of calculation
PDSI out of precipitation data, temperature and data of potential
evapotraspiration, to show the application of monthly values from Observatory in
Prague – Klementinum to calculating Palmer Drought Severity Index (PDSI) for
the period 1805 – 2000 (196 years) and it’s evaluation from the point of
view of time trends and occurrence of drought periods during the selected time.
It
indicates that the conditions of both spots are not much different to conditions
of the region in USA for which PDSI was implied. The fact that the index was
used for the first time in 1965 and is employed till now should suggest that its
construction is so sophisticated to be worthy for applying it also by us.
Key words: natural precipitation, temperature, evapotranspiration, and drought, Palmer Drought Severity Index
1. Introduction
Evaluation of Drought and drought its frequent theme of climatologic
works especially in semiarid areas. They often come in touch with dryness and
with caused economical damages, which often gain serious extent. In temporary
Middle Europe climate it is the top theme of interest of specialists and public
mostly after occurrence of drought and short after just till the next flood. In
spite of that we think that even in this conditions it is necessary to engage in
systematic research and work out due methods which can enable to signalise the
start of dry period and quick estimation of its importance in separate regions.
The
seek to achieve objectives of this article is to show the application of monthly
values of temperature and precipitation from Observatory in Prague –
Klementinum to calculating Palmer Drought Severity Index (PDSI) for the period
1805 – 2000 (196 years) and it’s evaluation from the point of view of time
trends and occurrence of drought periods during the selected time.
Klementinum
- Meteorological observatory in Prague is the working place, which gave the
oldest continually saved measurements of basic meteorological elements in the
area of Middle Europe. The regular and certain measurements of precipitation are
available from 1st May 1804. Some decennaries after were entered measurements of
precipitation in Jena (1827), Dresden (1828), Budapest and in Vienna (1841), in
Berlin (1847) etc. (PEJML 1975). Systematic temperature range is available even
from 1775. It is apparent that the mentioned well-knit time range is suitable
footing for numerable executions especially dealing with oscillation of
meteorological elements for more than 200 years period for the region of Middle
Europe.
2. Material
and Methods
One
of more used methods for drought evaluation especially in USA is Palmer Drought
Severity Index (PDSI). It was originally estimated for USA but we know from
recent times some works describing its application in Middle European conditions
(BRIFFA, K.R. 1994, HORVATH S., KLEMENTOVA E., LITSCHMANN T., 2001). Describe of
the construction and calculation PDSI is apparent from work for instance (ALLEY,
M.W. 1984). The Palmer Drought Severity Index was constructed by Palmer
estimating criteria in such a way that especially rainy month between dry
period does not influence too much the value of index. Similar it is when there
is a term of nearly normal precipitation following after dry period, which
does not mean that drought has finished.
Palmer´s
index regards climatic characteristics of the region as well as its basic soil
hydrolimits. It means that the same value of Palmer´s index in various regions
should have nearly the same economical impact. Its value varies in latitude from
– 6 to + 6. According to our experience, it can range also apart from those
limits in singular extreme cases. In Table 1 are shown the intervals of values
related to the worldly expressions representing precipitate character of the
period.
We
succeeded in obtaining the FORTRAN source program for calculating PDSI monthly
values from USA. We can now shape it according to our needs especially in
entering data and the outcomes as well as we can change empirical coefficients
and follow the impacts of the change to the result value PDSI. By studying the
source code we can better understand the global philosophy of the calculation
and use of separate equations. As entering data we used monthly values of
temperature and temperature from the station Prague-Klementinum for the period
1805 – 2000. Thornthwait Method implemented direct in the program using the
corresponding indexes related to the followed station calculated potential
evapotranspiration.
Tab.
1 Labelling the values PDSI
Palmer Classifications |
|||
4.0 or more |
Extremely
wet |
0.49 to -0.49 |
Near
normal |
3.0 to 3.99 |
Very
wet |
-0.5 to -0.99 |
Incipient
dry spell |
2.0 to 2.99 |
Moderately
wet |
-1.0 to -1.99 |
Mild
drought |
1.0 to 1.99 |
Slightly
wet |
-2.0 to -2.99 |
Moderate
drought |
0.5 to 0.99 |
Incipient
wet spell |
-4.0 or less |
Extreme
drought |
3. Results
and Discussion
Fig. 1 Monthly values
PDSI (Prague – Klementinum)
It is apparent that it is not typical climatological station and that is
why it is not possible to use the data coming out of it to the common time and
place processing. Its value is in integrated time range measurements suitable
for studying the oscillation of climate in recent centuries.
Palmer
Drought Severity Index is constructed in such a way that when it is
correctly calculated its values for the processed period are located nearly
symmetrically to zero level. It means that in chosen locality are alternating
dry and wet periods.
Fig.
2 Distribution curve of values PDSI for Klementinum (1805 – 2000)
From
Fig. 1 is apparent that in last 196 years were varying periods with overrunning
tendency to more dryness with periods more humid. That is why we decided to plot
the number of month in which the value of PDSI has decline under – 2 in
separate decennaries.
In Tab. 2 is chosen 10 months of the lowest values PDSI from the whole processed period. The year 1990 holds four places and the rest are divided to 2000 and 1826 three times each. The warning fact is that the last 11 years of processed period in the mentioned chart holds 7 places.
Year |
Month |
PDSI |
Year |
Month |
PDSI |
1990 |
8 |
-7,15 |
1926 |
8 |
-6,20 |
1990 |
7 |
-6,76 |
2000 |
9 |
-6,15 |
1826 |
9 |
-6,39 |
1826 |
10 |
-6,09 |
1990 |
9 |
-6,37 |
2000 |
6 |
-6,09 |
2000 |
8 |
-6,31 |
1990 |
10 |
-5,94 |
Fig.
3 represents the result of the processing and is quite conclusive. It documents
the presence of the months characterised as mild during last two decennaries and
is showing increase of drought from 1811.
The
situation is significant because the two decades followed consecutively and the
number of the months classified in such a way in every decade overrun half
of the total number. Greater number of dry months is evident already in 1971 –
1980 which followed after rather wet sixties which has interrupted for a while
the general increase of dryness from the years of forties.
Fig. 3 Number of month with values PDSI
under –2 in separate decennaries (Prague – Klementinum)
If
we can say that in curve of overrun values PDSI for the whole processed period
should be applied that the parameters respond to certain standards and do not
differ in separate localities
Fig.
2 the same must not be said for two separate selections from the whole file. We
have tried to divided the whole processed period to two parts. They are up to
1950 and from 1951 on.
The
result is on Fig. 4. and shows the increase of presumption drought in categories
mild drought and moderate drought (under – 2) nearly about 15%.
In
category extreme drought (under – 4) it is about 5% compared to previous
period. By K-S test we verified that the difference is significant on the level
0,05.
From
Fig. 1 we can assume that dry and wet periods are repeating in certain intervals
seemingly regularly. By a simple method, which is autocorelation, it can be
shown that the time range includes cyclic element, which has maximum in 111
month (9 and ¼ years) in its length.
As
shows the Figure 5 the maximum is slightly beyond the limit of significance. It
is related to low values PDSI in last decennaries, which appeared in 2000, 1990,
1984, 1974, 1964, 1954 and 1943 so nearly spacing related curve autocorelative
function.
Fig.
4 Comparison of curves of overrun values PDSI for the period 1805 – 1950 and
1951 – 2000 (Prague – Klementinum)
Fig. 5
Development of autocorelative indexes of monthly values PDSI (Prague –
Klementinum, 1805 – 2000)
4. Summary
By
application of calculations PDSI in Klementinum time range we succeeded to
figure some facts related to drought in Middle Europe region:
- Frequency
of dry months in last two or three decennaries gained maximum during the whole
processed period. It is significant that the mentioned decennaries are
consecutive.
- In
last 50 years occurred increase about 15 % of the months classified as mild
drought and extremely drought about 5 %.
- Seven
of ten most dry months from the whole processed period occurred in last 11 years.
-
The calculation of autocorelation showed that time range of values PDSI
holds cyclic element lasting nearly 9 and ¼ years. The same periodicity
corresponds with occurrence of dry periods in the second half of 20 century.
In
area dislocation of rains we can see greater variability and in analysing
Klementine time range is evident that more drought then in 2000 was about ten
years earlier. In 1947 was dry but in 1943 and 1954 were values PDSI even more
lowly. It probably was caused by the lack of objective method for evaluation of
drought and it has signs of subjective approach. Political situation or
interests of journalists can also influence the mentioned vision.
In
evaluating tendencies and long-term trends of drought is necessary to use the
longest time ranges. The length of one referenced period is for the mentioned
evaluation inadequate.
Acknowledgements:
The Grant Agency of
the Slovak Republic under the Project No. 1/9364/02 VEGA supported this study.
This support is gratefully
acknowledged.
References
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S.M. (1996): Evaluation of the Palmer Drought Index on the Canadian Prairies.
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Palmer Drought Severity Index: Limitations and Assumptions. Journal of climate
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Briffa, K., R. et all. (1994): Summer moisture variability across Europe, 1892-1991 an analysis based on the Palmer Drought Severity Index: International Journal of climatology, vol.14, 1994.
Carl
T.R. (1986): The Sensitive of the Palmer Drought Severity Index and Palmer´s
Z-Index to their Calibration Coefficients Including Potential
Evapotranspiration, Journal of climate and applied meteorology, Vol. 25,
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Horvath,
S. et all: Spatial and Temporal Variations of the Palmer Drought Severity Index
in southeast Hungary.
Klementová
E., Litschmann, T. (2001): Evaluation of drought regarding to complementary
precipitation. IXth International Landscape Conference, Lednice na
Moravě, 3. - 6. 9. 2001
Pejml, K.: The 200th Anniversary of the Prague-Klementinum Meteorological Observatory, HMÚ, Prague, 1975, 80 p.
AUTHORS
ADDRESSES:
Klementová,
Eva, Assoc. Prof. PhD., Department of Land and Water Resources Management,
Faculty of Civil Engineering, Slovak University of Technology Bratislava,
Radlinského 11, 813 68 Bratislava, Slovak Republic. Tel.: 0421-2-59274618, E-mail:
klement@svf.stuba.sk
Tomáš
Litschmann, RNDr., Amet. 691 02Velké
Bílovice, Czech republic, E-mail: amet@bva.sol.cz
Tel.: 00420-627-346252
Jaroslav
Rožnovský, Ing. RNDr., PhD. Czech
Hydrometeorological Institute, Brno, Kroftova 43, 616 67 Brno, Czech republic.
E-mail: roznovsky@chmi.cz