Abstract
In this study, changes in the spatial and temporal patterns of climate extreme indices were analyzed. Daily maximum and minimum air temperature, precipitation, and their association with climate change were used as the basis for tracking changes at 50 meteorological stations in Iran over the period 1975–2010. Sixteen indices of extreme temperature and 11 indices of extreme precipitation, which have been quality controlled and tested for homogeneity and missing data, are examined. Temperature extremes show a warming trend, with a large proportion of stations having statistically significant trends for all temperature indices. Over the last 15 years (1995–2010), the annual frequency of warm days and nights has increased by 12 and 14 days/decade, respectively. The number of cold days and nights has decreased by 4 and 3 days/decade, respectively. The annual mean maximum and minimum temperatures averaged across Iran both increased by 0.031 and 0.059 °C/decade. The probability of cold nights has gradually decreased from more than 20 % in 1975–1986 to less than 15 % in 1999–2010, whereas the mean frequency of warm days has increased abruptly between the first 12-year period (1975–1986) and the recent 12-year period (1999–2010) from 18 to 40 %, respectively. There are no systematic regional trends over the study period in total precipitation or in the frequency and duration of extreme precipitation events. Statistically significant trends in extreme precipitation events are observed at less than 15 % of all weather stations, with no spatially coherent pattern of change, whereas statistically significant changes in extreme temperature events have occurred at more than 85 % of all weather stations, forming strongly coherent spatial patterns.
Highlights
Changes in extreme weather and climate events have significant impacts and pose serious challenges to societies (CCSP10 Meteorological Service of New Zealand (MetService), Wellington, New Zealand11 Department of Atmospheric Sciences, Cochin University of Science and Technology, Cochin 682 016, India12 Centre for Oceans, Rivers, Atmosphere and Land Sciences (CORAL), Indian Institute of Technology Kharagpur, Kharagpur, India2008)
The variability of extreme temperature and precipitation events in Iran in recent decades was evaluated by Rahimzadeh et al (2009), who found negative trends for indices including frost/ice days (FD/ID), cool days/nights (TX10p/TN10p), and diurnal temperature range (DTR) over most regions of Iran
This study provides a comprehensive analysis of changes in temperature and precipitation extremes across Iran for the period 1975– 2010
Summary
Changes in extreme weather and climate events have significant impacts and pose serious challenges to societies River discharge trends showed an increase in mean discharge (31 to 35 %/decade) over the last decades For both northern and southern hemispheres at the same time, Choi et al (2009) evaluated the changes in means and extreme events of temperature and precipitation in the Asia-Pacific Network region during 1955–2007. The variability of extreme temperature and precipitation events in Iran in recent decades was evaluated by Rahimzadeh et al (2009), who found negative trends for indices including frost/ice days (FD/ID), cool days/nights (TX10p/TN10p), and diurnal temperature range (DTR) over most regions of Iran. Due to recent water shortages in Iran, including reduced water levels of lakes and alteration of major rivers to seasonal rivers, analyses of spatiotemporal changes in climatic extremes can provide crucial information for policy and decision makers
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