عنوان مقاله [English]
Climate change and global warming have affected extreme precipitation and temperature events at the local and regional scales in most parts of the globe. As a result, changes in the frequency and intensity of precipitation events occur in most parts of the world. Because of its direct effect on the water resources of the Earth, today it is necessary to detailed study on the behavior of these events. Therefore, the main objective of the present study is investigation of the homogeneity of rainfall data, determining the changes in extreme precipitation events in Khorasan South province and also calculation of the trends and statistical trends significancy of each of these indicators. The results of this study necessitate more management and planning for optimal use of available water resources. Today, with more than four decades of industrial rule over human societies, climate change, or global warming, has become a serious challenge to the planet's environment. The main reason is the intensification of human industrial activities. Increasing temperatures, melting polar ice, rising free water levels and irregularities in climate phenomena are the most important consequences of climate change. Due to the impact of climate change on a local and regional scale, support for climate change adaptation strategies and mitigating the adverse effects of this phenomenon has been considered today.
Materials and Methods
For this study, we used the long-term daily precipitation data in 6 active synoptic stations (Birjand, Nehbandan, Qaen, Boshruyeh, Ferdows and Tabas) in South Khorasan province between 1989-2018. Determination of the homogeneity/non homogeneity, finding the change points and adjusting the rainfall data time series were performed by using "RHtests-dlyPrcp" package, determination of trends observed in the extreme precipitation indices was done by using "RClimDex1.1" package and significancy test of the indices also was performed by Mann-Kendall nonparametric test and using the "trend" package in R software.
Then, 11 extreme precipitation indicators were calculated for selected stations and trends in precipitation events were determined. Finally, to investigate the impact of climate change, the significances of the trends in the indicators was measured using the Mann-Kendall statistical test. These indicators were approved by the World Meteorological Organization(WMO). Overall, extreme precipitation indices are classified in two categories. A number of indicators are based on rainfall intensity per unit "mm or mm/days"(Contains 6 index: PRCPTOT, SDII, R99p/R95p, RX1day/RX5day) and others are based on duration of precipitation or number days of precipitation that are based per unit "days"(Contains 5 index: CWD, CDD, R1mm/R10mm/R20mm). To determine the significant trends in each of the 11 extreme precipitation indicators for each station, Mann Kendall confidence level was considered 95%. The test statistic more than +1.96 and less than -1.96 indicated a significant trend.
Results and Discussion
The results showed that in most of the indices there were a decreasing trend. This trends were statistically significant in RX1day and RX5day(in Birjand and Nehbandan), R30mm(Ferdows and Nehbandan), R10mm (Birjand, Nehbandan and Boshruyeh) and PRCPTOT (for all stations). Despite decreases for R20mm, SDII and R95p (except for some indices), the behavior of these indices were not significant in any stations and for other indices a significant decreasing trend was observed only in one station. Overall, by calculating trends in rainfall events at stations of South Khorasan province, there were a significant decrease in total annual precipitation across the entire province, and days with precipitation greater than 10 mm, 1-day and 5-day maximum precipitation in the eastern half of the province that is affected by climate change. Therefore, it requires more management and planning for the optimal use of available water resources.
Global warming has caused disparities in the spatial distribution of rainfall and the changing behavior of rainfall events in south Khorasan stations over the last 30 years. The major changes in the indices show a decreasing trend. This decreasing trend is significant in some indicators. Most reductions are seen in the indicators RX1day, RX5day (Birjand and Nehbandan), R30mm (Ferdows and Nehbandan), R10mm (Birjand, Nehbandan and Boshruyeh) and PRCPTOT (for all stations). The south of the province is experiencing a significant decline in most of the indicators and is mostly affected by climate change, which requires more planning for efficient use of current water resources. The rest of the indices were either not significant (SDII, R99p and R20mm) or only significant at one station. So for the province, only a fraction of the changes in of extreme Precipitation Events are due to climate change.