Article

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: 3.4). 08/2008; 29(3):329 - 343. DOI: 10.1002/joc.1739

ABSTRACT 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 © 2008 Royal Meteorological Society

0 Bookmarks
 · 
191 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Based on daily precipitation dates at 42 meteorological stations in the Pearl River Basin, the spatial and temporal changes in precipitation index are analyzed during 1960–2012, eleven indices of precipitation extremes are studied. The results show that wet day precipitation, consecutive wet days and numbers of heavy precipitation days exhibit non-significant decreasing trends in the study area. Consecutive dry days and simple daily intensity index have increased and are significant at the 95% level, while other extreme precipitation indexes have non-significant increasing trends. Spatial changes of precipitation extreme indices show obvious differences, and they are not clustered either. On the whole, the number of rainy days has decreased over the Yunnan–Guizhou Plateau and hilly Guangxi, and the spatial distribution reflects the regional climatic complexity. Continuous wavelet transform analysis indicates that there are significant periodic variations with periods of ∼7 and ∼14 years in extreme precipitation, and that there is also a 6-year period and a 14-year period with the Pacific Decadal Oscillation (PDO) and Southern Oscillation Index (SOI), respectively, which are very consistent. The PDO and SOI are important influential factors for precipitation. In addition, except for consecutive dry days, the other extreme precipitation indices have significant correlations with annual precipitation. Large scale atmospheric circulation changes derived from NCEP/NCAR reanalysis reveals that a strengthening anticyclonic circulation, increasing geopotential height, weakening monsoonal flow, and vapor transportation over the Eurasian continent have contributed to the changes in precipitation extremes in southern China.
    Quaternary International 05/2014; · 2.13 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Extreme precipitation events have attracted a great deal of attention among the scientific community because of their devastating consequences on human livelihood and socio-economic development. To assess changes in precipitation extremes in a given region, it is essential to analyze decadal oscillations in precipitation extremes. This study examines temporal oscillations in precipitation data in several sub-regions of Iran using a novel quantile perturbation method during 1980–2010. Precipitation data from NASA's Modern-Era Retrospective Analysis for Research and Applications-Land (MERRA-Land) are used in this study. The results indicate significant anomalies in precipitation extremes in the northwest and southeast regions of Iran. Analysis of extreme precipitation perturbations reveals that perturbations for the monthly aggregation level are generally lower than the annual perturbations. Furthermore, high-oscillation and low-oscillation periods are found in extreme precipitation quantiles across different seasons. In all selected regions, a significant anomaly (i.e., extreme wet/dry conditions) in precipitation extremes is observed during spring. Ó 2014 Elsevier B.V. All rights reserved.
    Journal of Hydrology 10/2014; 519:1420-1427. · 2.96 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cities demonstrate higher nocturnal temperatures than surrounding rural areas, which is called “urban heat island” (UHI) effect. Climate change projections also indicate increase in the frequency and intensity of heat waves, which will intensify the UHI effect. As megacity Tehran is affected by severe heatwaves in summer, this study investigates its UHI characteristics and suggests some feasible mitigation strategies in order to reduce the air temperature and save energy. Temperature monitoring in Tehran shows clear evidence of the occurrence of the UHI effect, with a peak in July, where the urban area is circa 6 K warmer than the surrounding areas. The mobile measurements show a park cool island of 6-7 K in 2 central parks, which is also confirmed by satellite images. The effectiveness of three UHI mitigation strategies high albedo material (HAM), greenery on the surface and on the roofs (VEG), and a combination of them (HYBRID) has been studied using simulation with the microscale model ENVI-met. All three strategies show higher cooling effect in the daytime. The average nocturnal cooling effect of VEG and HYBRID (0.92, 1.10 K) is much higher than HAM (0.16 K), although high-density trees show a negative effect on nocturnal cooling.
    Advances in Meteorology 09/2014; 2014. · 1.24 Impact Factor

Full-text

Download
1 Download