International Journal of Agricultural Policy and Research
Vol.2 (10), pp. 334-345, October 2014
Article 13/ID/ JPR157, 012 pages
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 3.0 International License.
Original Research Article
Changes in precipitation extremes in climate variability over northwest Iran
M. Molanejad1,2, M. Soltani3, 4* and A. Ranjbar SaadatAbadi5
1Scientific Staff of Iranian Research Organization for Science and Technology (IROST).
2Director IORA- Regional Center for Science and Technology Transfer, Iran.
3Department of Physical Geography, Faculty of Geography, University of Tehran, Iran.
4Indian Ocean Rim Association (IORA), Regional Center for Science & Technology Transfer (RCSTT), Tehran, Iran.
5Atmospheric Sciences and Meteorological Research Center (ASMERC) of I. R. of Iran Meteorological Organization (IRIMO), Tehran, Iran.
*Corresponding Authors Email: soltani.clima(at)gmail.com
In this study, the spatial and temporal patterns of changes in the indices of precipitation extremes, on the basis of daily data and its association with climate change at twenty meteorological stations in northwest Iran over the period 1988–2012 were analyzed. Ten indices of extreme precipitation, which have been quality controlled, tested for homogeneity and missing data, were examined. Spatial distribution maps were drawn considering the sign of the changes and magnitude of each index at individual weather sites. Generally, the precipitation indices showed a decreasing trend in the amount, frequency and intensity of precipitation in most stations of northwest Iran. The results show that the summer average of precipitation across the region has increased by 1.55 mm, while the corresponding values for winter and annual precipitation indicate a decrease of 4.10 mm and 4.64 mm, respectively. About 90% of the heavy precipitation days (R10mm), and 85% of the very heavy precipitation days (R20mm) in the stations showed a decreasing trend. The trends of extremely wet days (R99p) for the stations in the mountainous areas were increasing, which means that precipitation intensity over these regions of the study area has increased, while precipitation frequency has decreased. About 10 out of 20 sites (50%) of the simple daily intensity index (SDII) had increasing trends with the magnitudes ranging from 0.05 mm/day to 0.103 mm/day. 75% of the sites (15 out of 20) showed decreasing trends in the numbers of consecutive wet days (CWD), which are consistent with those of consecutive dry days (CDD). In addition, the frequency of change magnitudes of R10mm, R99p, CDD, SDII, RX1day and PRCPTOT precipitation extremes over the region indicated a decreasing trend for the entire area, but it was statistically significant at some sites.
Key words: extreme precipitation, anomaly, climate variability, frequency, magnitude, RClimdex, northwest Iran