ENSO forcing on climate change in Iran: Precipitation analysis

An investigation was conducted to detect the change-point years in the Southern Oscillation Index (SOI) and precipitation time series in Iran for the period 1951-1999 (49 years). Due to the unavailability of data, the record length of the precipitation time series was not consistent for all stations, varying from 34 to 49 years. The Pettitt- Mann-Whitney and Mann-Whitney-Wilcoxon tests were applied to determine the significance of the detected changes. The difference in SOI and precipitation amounts for the period before and after the change years was investigated. The coincidence of change-point years in the SOI time series and precipitation data was explored to evaluate the possible forcing effects of the El Niño-Southern Oscillation (ENSO) phenomenon on the suppression or enhancement of Iran's hydrological cycle. The results indicated that the mid 1970s are the most probable change- point years in the time series of Southern Oscillation Index (SOI) data. The frequency and intensity of El Niño events have increased since then. Consistent with this finding, precipitation data from both south-western and northern parts of Iran have also shown significant change years in or around the mid 1970s. Compared to the period before 1975, annual precipitation over most of the studied regions has increased. This increase was found to be more considerable in southern rather than northern districts. Seasonal precipitation amounts in southern regions have generally increased during autumn and winter and decreased in spring. On the other hand, for northern regions, precipitation has increased during summer and autumn and decreased throughout winter and spring. The most enhanced portions of the hydrological cycle in the southern and northern regions were centred on March and May, respectively

Spatial patterns and temporal variability of drought in Western Iran

An analysis of drought in western Iran from 1966 to 2000 is presented using monthly precipitation data observed at 140 gauges uniformly distributed over the area. Drought conditions have been assessed by means of the Standardized Precipitation Index (SPI). To study the long-term drought variability the principal component analysis was applied to the SPI field computed on 12-month time scale. The analysis shows that applying an orthogonal rotation to the first two principal component patterns, two distinct sub-regions having different climatic variability may be identified. Results have been compared to those obtained for the largescale using re-analysis data suggesting a satisfactory agreement. Furthermore, the extension of the large-scale analysis to a longer period (1948–2007) shows that the spatial patterns and the associated time variability of drought are subjected to noticeable changes. Finally, the relationship between hydrological droughts in the two sub-regions and El Niño Southern Oscillation events has been investigated finding that there is not clear evidence for a link between the two phenomen

ENSO’s Impact on the Occurrence of Autumnal Drought in Iran

Recent extreme rainfall events and the frequent occurrence of worldwide droughts and their associated natural disasters (i.e., devastating bushfires in Australia, Indonesia, and Italy during 1997; the current severe drought in Iran) have increased the scientific community’s interest in the broad characteristics of rainfall variation and the potential for rainfall prediction. On the basis of the Koppen climate classification (Ahrens, 1998), the Islamic Republic of Iran (Figure 1) is categorized as generally having arid (BW) and semiarid (BS) climates. This signifies that the annual precipitation is less than the potential annual loss of water through evapotranspiration. The occurrence of rainfall is unreliable and deviations from the mean are generally more than 40%. The average annual precipitation over the country is estimated to be about 250 mm (about one-third of global annual precipitation). Iran, with an area of 1,648,000 km2, lies predominantly within a portion of the Alpine–Himalayan chains, including the major mountain systems of the Alborz and Zagros ranges (Figure 2). As indicated in this figure, the central part of Iran, which is surrounded by these ranges, comprises two uninhabited deserts, Dasht-e Lut and Dasht-e Kavir. In spite of severe dry conditions over these regions, the Zagros and Alborz highlands, like the coastal strip of the Caspian Sea, are classified as having a Mediterranean climate (Csb) and usually receive moderate precipitation

Winter Drought in Iran: Associations with ENSO

The Islamic Republic of Iran (Figure 1) has an area of 1,648,000 km2 and a population of 65 million people (1995 estimate). The country has arid and semiarid climates and the occurrence of rainfall is unreliable, with a coefficient of variation as high as 70%. The average annual precipitation over the country is around 250 mm. Two mountain ridges, the Alborz and Zagros (Figure 1), which run east and southeast from the northwest corner of the country, play an influential role in determining the amount and spatial distribution of rainfall. The peaks of Alborz and Zagros are about 5,700 m and 4,000 m, respectively. Rainfall generally occurs from October to March (winter), with extreme events during January and February. Annual rainfall over the northern sides of the Alborz range may reach 1,800 mm, but for the central and eastern deserts, the yearly total is around 50 mm. Droughts and floods are common, and the severity and hardships of these natural disasters frequently hit both rural and urban societies. Drought limits dryland farming and affects the productivity of irrigated lands. Moreover, due to massive overgrazing, large-scale soil erosion occurs during dry spells. Atmospheric and climatic incidents (i.e., floods, droughts, and lightning) account for about 97% of all natural disaster costs. Concern about water resources is currently realized as one of the most important issues for most of the Iranian scientific and management communities. Most parts of the Islamic Republic of Iran recently experienced an exceptional drought that lasted more than 2 years (1998–2000). In some areas, drought has also extended into winter 2001. The 1998–2000 drought inflicted $3.5 billion in damages, killing 800,000 head of livestock and drying up major reservoirs and internal lakes (Pagano et al., 2001). Nazemosadat and Cordery (2000a) and Nazemosadat (1999) have recently revealed that the autumn rainfall in Iran is negatively correlated with the Southern Oscillation Index (SOI). The relationships were found to be strong and consistent over the southern foothills of the Alborz Mountains, northwestern districts, and central areas. Since winter rainfall contributes a major portion of Iranian water resources, the shortage of rainfall during this season is the most important cause of drought in Iran. Nazemosadat and Cordery (2000b) have therefore focused on the impact of ENSO on winter precipitation in Iran. The present study outlines some key results of the aforementioned studies

INDIVIDUAL AND COUPLED EFFECTS OF THE ENSO AND PDO ON THE INCIDENCE OF AUTUMNAL DRY AND WET PERIODS IN IRAN

The El Niño-Southern Oscillation (ENSO) is strongly connected to the inter-annual to intra-seasonal variations of Sea Surface Temperature (SST) over the Pacific Ocean equators. On the other hand, the Decadal Pacific Oscillation (PDO) is related to quasi-decadal fluctuations of the Pacific SSTs in the north-eastern parts of the ocean. The present study has made an effort to analyse the individual and the coupled effects of the ENSO and PDO on autumn precipitation in Iran for the period 1951-2005. Total precipitation data was collected for 41 rain-gauge stations spread in various parts of the country. Moreover, concurrent SST anomalies over the Niño 3.4 region were used as the ENSO indicator. Years related to the rank 1 to 18and 37 to 55 (18 years each) were categorized as the ENSO negative (El Niño) and positive (La Niña) phases, respectively. After obtaining the PDO data, similar procedure was also used to detect 18 years of the high or low phase of the PDO (PPDO or NPDO, respectively). The events that El Niño or La Niña years were coincided with the positive or negative phase of the PDO were then investigated. The results indicated that, precipitation has significantly suppressed or enhanced during the La Niña or El Niño event, respectively. Although the above or below normal precipitation was generally coincided with the PDO positive or negative phase, the effects of this Oscillation on precipitation variability were generally found to be significant for south-east rather than south-west of the country. While precipitation variability in south-west parts of the country was more sensitive to ENSO, the PDO was more influential on precipitation variability in southeast districts. The more dry or wet event was recognized as the periods that La Niña or El Niño is, respectively, coincided with the negative or positive phase of the PDO (La-LPDO and El-HPDO

Workshop on Drought-Related Issues in Fars Province, Iran: Critical Points and Resolutions

As a result of the occurrence of overwhelming severe drought over most parts of the Islamic Republic of Iran, an educational/professional workshop on drought issues was held at the College of Agriculture, Shiraz University in Iran, October 18–19, 2000. The workshop was sponsored by the College of Agriculture, the office of Fars Provincial Government, the Agricultural Bank, and Shiraz Abfa Company. The workshop was mainly focused on the assessment of drought impacts and severity in Fars province, in the southern part of Iran. The inauguration ceremony was attended by some of the parliament members (from Fars province), the Chancellor of Shiraz University and his deputies, the construction deputy of Fars Government, the director of the National Disaster Office (NDO), the NDO staff in Fars Province, general managers from various departments of the province, postgraduate students, and about 400 professional staff from various disciplines. All sessions, including the closing session, were well attended by the participants

Effects of El Nino Southern Oscillation on the Discharge of Kor River in Iran

The objective of the study was to investigate the El Nino forcing on the discharge of Kor River located in Maharloo-Bakhtegan basin in the Fars province of Iran. Thirty-one-year (1965-1995) and twenty-year (1975-1995) monthly mean river discharge data recorded at two stations, namely, Chamriz and Dehkadeh-Sefid, respectively, were chosen in the present study. Fourier analysis was used to extract harmonic information of time series data such as amplitude and phase angle to show the maximum effect and the time of effect of El Nino on river discharge. The study revealed that El Nino events caused increase of discharge in Kor River by 15% to 20% and the maximum influence was in the months of February and March in El Nino year