A Preview of Iran` s Climate Using SIAP Method

Behrooz Sari SarrafAssociate Professor in physical Geography Department, Islamic

Azad University _ Ahar BranchAbbas Hosseini Shamechi

Assistant Professor in physical Geography Department, Islamic Azad University_Ahar Branch

Masoomeh EmamgholizadehM.A in physical geography. University of Tabriz

Abstract

The study of climatic data and influences and their likely changes in different period of times, providing the better understanding of nature.In the existing study, after reconstructing and applying homogeneity tests on the long term period of the precipitation records in all synoptic stations of Iran, and using the SIAP (Standard Index of Annual Precipitation) Method. Finally zoning map of Iran based on standardized values and the coefficients of variation of precipitation have been plotted.According to the results obtained, in the years 1966 and 1973 all over Iran has experienced droughts and since 1995 until 2001 a very long desiccation in most parts of Iran has dominated.

In the present study the rainfall statistic of 30 synoptic stations in Iran through 43 years statistical period from 1961 to 2003 is used for order to determine Iran’s regional drought periods and its zoning based on weight variation coefficient.The statistical data loss in the study area was reconstructed by using least difference method and linear correlation method and then homogenous test applied on them. In this research in order to determine the drought region in Iran tow formulas are used:Consequently the Iran’s map of weight of variation coefficient curves is drawn.

Methodology

Discussion

Drought is one of the climatic oscillations and the lack of knowledge about this phenomenon will impose great economic and natural loss to a region.Especially in Iran that is located in the desert belt of earth and its economic infrastructure without considering petroleum is agricultural productions, for this reason using a long term statistical period’ the drought in Iran has been evaluated. The local distributing of rainfalls in Iran is very diverse and particularly, taking into account that a large part of the country have lower rainfalls. Alijany (2000) has divided Iran in to six climatic regions by considering a number of rainfall characteristics and using synoptic procedure. (Table1)

Table1: rainfall regions in Iran

Arid zone Zahedan – Kerman –Bandar abbas –

Semnan –Yazd – Esfehan –Bushehr –Ahvawz –Shiraz- Tehran – Qom

11

KurdistanSanandaj – Kermanshah – Eilam –Khorram abad4

Azerbaijan regionOrumieh – Tabriz –Arak – Qazwin-Zanjan– Shahr e kord – Mako - Hamedan8

North KhorasanMash’had1

Eastern CaspianBabolsar – Gorgan –Sari3

Western CaspianRamsar –Rasht -Ardabil3

Rainfall regionStation namesThe number of stations

Reference: Alijany 2000

Map 1- The location of researched stations

For estimating annual rainfall the following formula is used:Asy = (Rsy-Rs)/ σs or:

SIAP = (Pi-P)/SD The results of formula calculation in brought in diagram 1:

Diagram1- standardized Values

The humidity in Caspian Sea region covers only its coastal sections. Therefore; the quantity of precipitation reduces from west to east because the air mass coming from Siberia is initially dry first; when it passes over warm sea it absorbs moisture and causes plenty of rainfalls in the western part of Caspian sea. As a result the stations such as Rasht, Ramsar are Humid, Babolsar, Sari are sub- humid and Gorgan is semi- arid. Table 3 shows Iran’s regional drought map in accordance with SIAP standard values. Iran is divided into four regions including: very dry, semi-arid, sub- humid and humid.

Humid Ramsar- Rasht2

Sub- humid

Sary- Babolsar- Ardebil- Euromieh-Tabriz- Shahr-e-kurd- Eilam- Khorram

abad- Mako-Sanandaj- Kermanshah11

Semi- arid

Mashhad- Gorgan-Tehran- Zahedan-Semnan- Bandar abbas- Shiraz- EsfahanBooshehr- Yazd- Ahvaz- Arak- Hamadan-

Qum- Qazwin- Zanjan

16

Very DryKerman 1

Rainfall regionStation nameThe number of stations

Table 2- Regional division of Iranian Climate on SIAP

Map2- Zoning the drought phenomenon in Iran

The precipitation variability shows the deviation amounts from average and provides an image of precipitation regime. High degree of variability is usually an uncertainity factor for agriculture. The

precipitation variability was determined by following formula: CV= (σs /Rs).100 %

By calculating Variability Index in the study stations, we obtained the results that are shown in Diagram 2 and Map 3:

Diagram2- The Precipitation Variation Index

Map 3- Coefficient Variations of Iran’s Precipitation

The precipitation in Iran also can be investigated by means of entering air mass paths. Iran's air mass charts for different seasons: Following area, chart 1 indicates autumn and winter; chart 2 indicates spring and chart 3 shows summer season.

The study of dominant air masses in Iran shows that in autumn and winter they include Westerly as well as Siberian air masses. Westerly air masses enter Iran from west and Mediterranean Sea and causes winter precipitation. Similarly, the Siberian air mass enters Iran from north and north east and mainly influences Caspian precipitation.

Conclusion

The results obtained show that the drought dominated in Iran in 1961 and 1962 mostly in the west part of the country that is influenced by higher levels of atmosphere. Severity of drought in 1966 and 1973 was more; in 1982 the severity reduces that is associated with more precipitation in many stations. During the statistical period; the driest years were from 1995 to 2001 since the year 2002 the severity of drought reduces.

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