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. Molanejad^{1, 2}, M. Soltani^{3, 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

Abstract

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