Variability of extreme temperature and precipitation in Iran during Recent decades

Atmospheric Science and Meteorological Research Centre (ASMERC), Tehran, Iran
International Journal of Climatology (Impact Factor: 3.16). 03/2009; 29(3):329 - 343. DOI: 10.1002/joc.1739


We examined extreme temperature and precipitation as indicative climatic variables to determine recent climatic changes over Iran. We present the results from 27 synoptic stations which have been quality controlled, tested for homogeneity and have less missing data. For each station, 27 indicative climatic indices recommended by the joint World Meteorological Organization CCL/CLIVAR/JCOMM Expert Team on Climate Change Detection and Indices (ETCCDI) were calculated.
Marked negative trends for indices like frost days (FD), ice days (ID), cool days (TX10p), cool nights (TN10p) and diurnal temperature range (DTR) were found over most regions of Iran. Conversely, positive trends were found for summer days (SU25), warm days (TX90p) and tropical nights (TR20) over most regions of the country. For indices such as Cold Spell Duration Index (CSDI) and Warm Spell Duration Index (WSDI), both positive and negative trends were obtained.
We found negative trends in consecutive dry days (CDD) over most of the country. A negative trend was observed for about two-thirds of the country for annual total wet days precipitation (PRCPTOT). Positive trends in the Simple Daily Intensity Index (SDII) were found for the northern half of the country, and concurrently negative trends in total wet days for many places within the same region. We observed a negative trend in very wet days exceeding the 95th percentile (R95p) over the eastern and western regions, and a positive trend over the central region of the country, although a clear negative trend was observed for extremely wet days exceeding the 99th percentile (R99p) over most of the country. No similar trends in either the maximum 1-day precipitation (Rx1DAY) or maximum 5-day precipitation (Rx5DAY) were found over the country. Copyright

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    • "This opportunity gives many possibilities for further applications especially for distributed modeling of environmental processes (Debesch et al. 2010). There are many studies on temperature extremes in Iran on regional and global scales without using of climatic gridded data, e.g., Alexander et al. (2006), Zhang et al. (2005a), Rahimzadeh et al. (2009), and Marofi et al. (2011). Their results have indicated that the temperature indices are consistent with global warming. "
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    ABSTRACT: An investigation of climatic extreme events presents the valuable opportunities to evaluate the potential impacts of climate change on human activities, agriculture, and economy. These analyses are useful procedures in monitoring climate change on a synoptic scale. The present study is a trend analysis of the extreme temperature events, which have been based on the gridded daily temperatures of Iranian climatic database within 1962–2004. The aim of the present study is to identify the frequency and intensity of extreme events, which have been increased with over Iran in the last four decades. Both the Mann–Kendall trend test and simple linear regression were utilized to detect trends in annual temperature extremes. The results showed that the frequency of hot extreme temperature events has increased over the studyarea within 1962–2004, while a negative trend has been observed in the frequency of cold extreme temperatures. About 66 % of the surface area has a significant positive trend in frequency of hot days and nights, while about 40.9 and 68.5%of surface area have a significant decrease in frequency of cold days and nights, respectively. The strongest increasing tendency is detected in the case of the annual numbers of hot nights, warm nights, summer days, warm days, and the heat wave duration indices.
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    • "The method has been used by many investigators for trend analysis in meteorological time series and found to produce reasonable results (e.g. Hirsch et al., 1982; New et al., 2006; Rahimzadeh et al., 2009; Chaouche et al., 2010; Kumar and Jain, 2010; Xu et al., 2010; Tabari and Talaee, 2011; Patra et al., 2012; Rehman et al., 2012; Mackellar et al., 2014). Details of the method appear in many peer-reviewed papers; however, to make this paper self-contained, the mathematical expressions of the Mann–Kendall test statistics S and Kendall tau coefficient í µí¼, appear in Appendix A. The annual and seasonal indices computed from the monthly data as given by the outputs of the RClimDex software were used as input in the R-package 'fume'. "
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    ABSTRACT: This study analyses spatial and temporal trends in extreme temperature indices over Nigeria. The percentile indices were calculated from newly homogenized daily minimum and maximum temperature data for the period 1971–2012 for 21 stations in Nigeria. Indices describing the characteristics of hot extremes and cold extremes are calculated with the RClimDex software. The annual and seasonal trends in these indices are obtained using the ordinary least square fit and the statistical significance tested using the R-based modified Mann–Kendall test. We examine characteristics of these indices for the entire country and separately for the three geographical zones in Nigeria: Guinea, Savanna, and Sahel. The spatial and temporal patterns of trends in the indices indicate that Nigeria has experienced statistically significant increase in the frequency of hot extreme and decrease in cold extreme events. Although majority of the stations have significant trends in warm days and warm nights, the annual trend is greatest in warm nights. In addition, the rate of warming in minimum temperature (‘warm nights’) is stronger in June, July, August (JJA) and September, October, November (SON) compare with December, January, February (DJF) and March, April, May (MAM). As for the trends in cold days and cold nights, the trends in cold nights are larger than for cold days at both the annual and seasonal scales. The regional analysis indicates that trends in warm nights and cold nights are most pronounced in Guinea and Sahel regions.
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    • "Their results indicated that the annual rainfall decreased at 67% of the stations; however, the 24-h maximum rainfall increased at 50% of the stations. By studying 27 synoptic stations in Iran over 1951–2003, Rahimzadeh et al. (2009) showed overall negative trends of very wet days defined as the fraction of annual total precipitation that exceeds the 95th percentile (except for the central regions) and the 99th percentile. They also found negative trends in the maximum precipitation in the southern regions of the country, and mixed positive and negative trends in the northern parts. "
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    ABSTRACT: Spatiotemporal changes in total precipitation as well as the magnitude and frequency of extreme precipitation events in Iran are assessed using 187 gauging stations with at least 41 years of records until 2009. The spatial distribution of extreme precipitation is evaluated based on the generalized extreme value (GEV) distribution fitted to the annual/seasonal maximum daily series at each location. Temporal trends of the magnitude of extreme precipitation events are also analysed using the annual/seasonal maximum daily series, while temporal trends of the frequency of extremes are assessed based on records exceeding the 99th percentile threshold. Results show an overall declining trend of the annual precipitation in particular in regions located on the north, west and northwest of Iran. Seasonal analysis shows the largest contribution of winter to this declining trend. In addition, precipitation has significantly decreased in the northwest during spring. Although the changes in the magnitudes of extreme precipitation events are insignificant, with increasing trends in 50% of the stations, the overall frequencies show significant declines in particular during winter. The magnitude and frequency of extreme precipitation have also significantly declined in the northwest region during spring.
    Full-text · Article · Sep 2015 · International Journal of Climatology
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