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July
2014 Volume 3 Issue 2
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Molanejad M
Abadi ARS
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Gobal Advanced Research Journal
of Environmental Science and Toxicology (GARJEST) ISSN:
2315-5140
July 2014 Vol. 3(2), pp.
025-037
Copyright © 2014 Global Advanced Research Journals
Full Length
Research Paper
Characteristics and mechanism of extreme climate events
under climate change background in Iran - part I: drought
M. Molanejad1, 2,
M. Soltani3, 4* and A. Ranjbar
Saadat Abadi5
1Scientific
Staff of Iranian Research Organization for Science and
Technology (IROST)
2Director
IORA- Regional Center for Science and Technology Transfer
3Indian
Ocean Rim Association (IORA), Regional Center for Science
and Technology Transfer (RCSTT), Tehran, Iran
4Department
of Physical Geography, Faculty of Geography, University of
Tehran, Iran
5Atmospheric
Sciences and Meteorological Research Center (ASMERC) of I.
R. of Iran Meteorological Organization (IRIMO), Tehran, Iran
*Corresponding author’s email:
soltani.clima@gmail.com
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Abstract |
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Drought is a natural disaster that gives a lot of
damage every year. It is one of the most dangerous
natural hazards because it is very difficult to
identify its onset. In this paper the Standard
Precipitation Index (SPI) has been used to
monitor drought in Iran. The SPI index is a powerful
tool, requiring only rainfall data for its
calculation, and delivering major dimensions of
drought such as severity, magnitude, frequency etc.
Thirty five years (1978 to 2012) of monthly
precipitation data of 30 stations across Iran are
used to calculate SPI values for a time-scale of 12
month period. The time series plots of SPIs
indicated that a negative trend of drought (an
increase in drought frequency) over the country
except for the central and southeastern parts, where
a positive trend and decrease in the frequency of
drought observed for those areas. Furthermore, the
year 2010 was detected as the driest year in terms
of drought severity with values varying between
-2.524 and -4.933 that approximately 80% of the
stations had a negative trend in which 75% out of
80% was statistically significant during the
examined period over Iran. The results also
suggested that the drought severity is very critical
in the Western areas in particular in Ilam region.
As well as, we found that the mountainous regions,
in general, are more vulnerable to drought
phenomenon rather than other parts of the country.
The
synoptic
features at 500 hPa and surface levels
of the
extremely dry (the severest drought) year i.e.
2010
proved that no suitable rising condition was
provided during the mentioned year, because of the
formation of a belt of high pressures over Iran as
well as the expansion of the Siberian high pressure
center southwestward. Consequently, no considerable
amount of moisture transferred to the country, and
as a result, the lowest amounts of the annual
precipitation were recorded at the thirty selected
stations during the examined period across Iran.
Keywords:
Drought, standardized precipitation index,
frequency, severity, synoptic pattern, Iran
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