جستجوی مقالات مرتبط با کلیدواژه "modified mann" در نشریات گروه "کشاورزی"

Due to global warming, and its resulting changes in the frequency and amount of precipitation and temperature, there has been a great concern on climate change impacts by the scientific community. This study focuses on trend analysis of annual and seasonal rainfall (P), maximum temperature (Tmax) and minimum temperature (Tmin) time series from seven meteorological stations in Gorgranrood river basin during 1982-2011. Three statistical tests including, Mann-Kendall (MK), the Modified Mann-Kendall (MMK) test and Man Wintney (MW) were examined at 10% significance level. To quantify the slope we used Sen’s non-parametric estimator of slope. Both positive and negative trends were identified by all the tests. However, all negative trends were insignificant and only some positive trends were significant. Trend tests reveal that the median of slopes of seasonal series of Tmax, Tmin and P are located above zero line which is revealed that increasing trend is observed in most of the station Steepest positive slope of trend line of the Tmax is found in the spring then in summer time. Trend analysis has revealed strong seasonal variability of Tmin series. The highest number of stations with significant trends occurred in the Tmin while less significant trends were detected in the Tmax and P. There is a non-significant increasing rainfall trend in the basin. With regard to seasonality P, it is remarkable that positive significant trends were detected in few stations at both annual and seasonally time scale. In order to remove serial correlation, the trend-free pre-whitening procedure has been applied and less number of positive trends has been again observed, highlighting that, in this case, serial correlation affect the results of Mann-Kendall trend test.

Within the climate change debate and its probable impacts on water resources systems, design and operation of management plans based on the assumption of stationary hydrology may cause serious challenge to accurately predict future supplies. Therefore this case study is trying to assess trend in hydroclimatic variables of Karkheh Rivers upstream by applying modified Mann-Kendall trend test on long term daily time series of temperature, precipitation and discharge. Temperature variables are mostly showing meaningful increasing trends but observed changes in assessed stations were not spatially uniform for precipitation. Streamflow variables depict a decreasing trend, though more noticeable in base flows. Decreasing trend is meaningful for annual discharge median in Holailan at 90% confidence level. Total yearly precipitation, number of precipitation days and number of days with precipitation equal to, or greater than, 10 mm/d show the most correlation with stream flow variables. Comparing monthly discharge with temperature and precipitation variables in the studied gages indicates a time-delay in system response to inputs. This may related to snowmelt contributions or contributions of water into streams after passing through different hydrological pathways such as groundwater. Some parts of streamflow changes, especially about base flows, is not completely verified by precipitation changes and can be attributed to changes in temperature or another factors such as groundwater overexploitation.

The present study is mainly concerned with the changing trend of temperature of Iran based on NCEP data from atmospheric general circulation model under A1B scenario. The date were divided into two periods 1961-1990 and 1991-2050 and for each periods، modified Mann-Kendall test have been used together with the Sen’s Slope Estimator for the determination of seasonal trend and slope magnitude، then the resulting values for each grid point of atmospheric general circulation model network were classified The result showed that in the first period، trend were detected only in summer and winter seasons in some area but in the second period، trend were detected in all of season and area. Also slope of train line were greatest in summer and smallest in winter and this gradient in west and southwest of Iran greater than other area. Keywords: Sen’s Slope Estimator، Air Temperature، Trend، General Circulation Model، Modified Mann-Kendall.