The Impact of Climate Change on Extreme Precipitation Events in Khorasan Razavi Province (Case study: 1975-2013)

The assessment of extreme climatic events variations due to its effects on the human life, economy, natural ecosystems, and also extensive spatial and temporal changes in recent decades under the impact of global warming have been a major issue around the world (Rosenzweig et al., 2001; Aguilar et al., 2009; Zwiers et al, 2013). Therefore, the main objectives of the present study are to investigate the homogeneity of rainfall data, determine the changes in extreme precipitation events in Khorasan Razavi province, and also calculate the trends and the significance of statistical trends of each of these indicators. The result of this study could be very essential especially for the water resources, agriculture and forestry that are affected by this phenomenon and its climatic changes. For this study, we used the long-term daily precipitation data in 3 synoptic stations (i.e., Mashhad, Torbat Heydariye, and Sabzevar) and 6 evaporative stations (i.e., Mareshk, Zoshk Khorasan, Barerye Chahar Bagh, Baghsangan Torbat Jam and Farhadgard Fariman), between the years 1975-2013. Determination of the homogeneity/non-homogeneity, finding the change points and adjusting the rainfall data time series were performed using RHtests-dlyPrcp package. The determination of trends observed in the extreme precipitation indices was done using RClimDex1 package and significance test of the indices was performed using Mann-Kendall’s nonparametric test and the Trend package in R software. In this study, eleven extreme precipitation indicators were calculated and studied for selected stations in Khorasan Razavi. These indicators were approved by the World Meteorological Organization. Generally, extreme precipitation indices are classified in two categories; a number of indicators are based on rainfall intensity per mm or mm/days (i.e., contains six indices: PRCPTOT, SDII, R99p/R95p, RX1day/RX5day) and others are based on duration of precipitation or number of precipitation days that are based on days (i.e., contains five indices: CWD, CDD, R1mm/R10mm/R20mm). To determine the significant trends in each of the eleven extreme precipitation indicators for each station, Mann Kendall’s confidence level was considered to be 95%. The test statistic higher than +1.96 and lower than -1.96 indicated a significant trend. R1mm, R10mm, RX5day and RX1day indicators showed significant trends (mainly increasing and sometimes decreasing) in most of the stations. PRCPTOT, SDII, R20mm and R95p indicators showed significant trends in half of the stations. In most of these stations, increasing trends were observed except for SDII. CWD, R99p and CCD Indicators showed significant trends only in a few number of stations. These trends were increasing for CDD and decreasing for CWD. Most indicators did not show significant trends while they had slightly decreasing trends. Such indicators showed lower levels than-1.96, and then were not significant at the 95% confidence level. Sabzevar station did not show significant trends in any of the extreme precipitation indicators. Zoshk, Pangaje Abshar and Farhadgard stations showed significant increasing trends with high intensity (great increasing slope) in the most of the indicators. Due to the effect of climate changes, global warming and uneven spatial and temporal distribution of rainfall, extreme precipitation indices showed different changes and inconsistency in Khorasan Razavi stations. Some stations showed increasing trends in each index and others showed decreasing trend. Some indicators had significant trends in a station and the others did not. PRCPTOT, SDII, R20mm and R95p indicators showed statistically increasing trends in most stations. However, no indicator showed significant trends in Sabzevar station.