عنوان مقاله [English]
نویسندگان [English]چکیده [English]
recent long successive drought in the southern part of Iran including Fars province, necessitate the need for water resources management. The wide changes in climate variables in the daily, monthly and yearly scales show the relationship of these factors with the atmospheric and oceanic teleconnection patterns such as ENSO, Arctic Oscillation (AO), the Antarctic oscillation, North Atlantic Oscillation (NAO), Madden-Julian Oscillation (MJO) and …. Madden-Julian oscillation, Oceanic Remote Link phenomena and stable patterns are caused by general circulation of the atmosphere. This phenomenon is mainly detected by the release of east side of an area of strong convection with the intensification of rainfall over the Indian and Pacific Ocean. The positive anomalies of rainfall first started in some parts of east Africa and West Indian Ocean and then spread to the east. In many researches in this field, main focuses have been on the relationship between temporal and spatial distribution of precipitation with MJO event's status. However there has been less attention to influence of the MJO on runoff in the country. While the amount of runoff is one of the main components of the hydrological cycle and plays key role in water resources management, agricultural planning, optimal utilization of dams and etc. Here the main objective is studying the influence various phases of the MJO on rainfall and runoff of the rivers in the Fars province of Iran.
The daily data of hydrometric stations of Doroodzan, Pol-Khan, Cham-Chit, Bvshigan, Chiti, and rain gauge station of Bvshigan, Chiti, Chamriz, Farashband, Sad-Abad and Gere-Bala of these rivers were collected from the Fars Regional Water Office. Here the stations which had at least twenty years data and had a minimum number of missing data are used. In this study, the focus has been on the critical period of Madden-Julian Oscillation in the rainy seasons (October to March) from 1975 to 2015.The daily MJO index from Bureau of Meteorology are used to select critical period of eight phases of the MJO with conditions as the magnitude of the MJO index remain larger than 1 and the similar phase for the MJO at least in five days. Also ANOVA test were used to study the significant effect of eight phases of the MJO on the amount of rainfall and runoff of the rain gauges and hydrometric stations. Then LSD test was used to compare the differences between averages of the each selected groups. Finally, deviation and percentage deviation from the mean value were used to quantify the impact of each phase on the precipitation and runoff.
The results of ANOVA test for rain gauges stations in Sad Abad, Jere-Bala, Farashband, Bvshigan, Chiti and Chamriz stations showed that the null hypotheses (equality of rainfall means in MJO phases) is rejected, accordingly we can conclude that the impact of MJO on the rainfall of selected stations is significant. This test for hydrometric stations of Pol-Khan, Dorood-Zan, Cham-Chit, Chiti, Chamriz and Bvshigan showed the significant impact of Madden-Julian oscillation on the runoff of Fars Province Rivers, too. Here null hypothesis of equality mean of runoff in hydrometric stations is rejected and LSD test confirmed the significant differences between the mean values in eight phases of the MJO.The result obtained from the hydrometric stations of Chiti and Bvshigan showed that phase 8 and 5 of the MJO has greatest positive and negative impact on the runoff of the rivers respectively. In Doroodzan and Pol-Khan hydrometric stations, the greatest negative impact on runoff is seemed in phases 5 and 7 of the MJO. The analysis of rain gauge data of Bvshigan and Chiti showed most precipitation (relative the mean value) in the phase 8 of the MJO which indicate positive impact of this phase of madden-Julian oscillation on rainfall value. The most negative deviation from the meam value is seen in the Phases 3 and 4 of the MJO in the stations of Bvshigan, Sad-Abad and Chiti respectively which shows negative impact of the MJO. In Farashband station of Dalaki river, phases 7 and 8 had the greatest positive and negative impact respectively. Generally, statistical analysis showed that there is a significant difference between the mean of rainfall and runoff value in various phases of the MJO in the selected rain gauge and hydrometric stations. In summary the analysis of the results in the hydrometric stations showed that the phases 1 and 8 of the MJO have the greatest positive impact and the phase 5 has the greatest negative impact on rainfall. For rain gauge stations, the results showed that the phases 7 and 8 of the madden-Julian oscillation has the most positive impact on rainfall amount and the phases of 3 and 5 of this oscillation has the most negative impact.
So it is reasonable that at first MJO causes to increase precipitation amount in south of Iran in phases 7 and 8 then in two later phases (8 and 1) the increase in runoff value is seemed because of existence a lag time to convert rainfall to runoff.