Trends in rainfall at 39 locations of the Nile River Basin (NRB) in Africa were analyzed. Compari... more Trends in rainfall at 39 locations of the Nile River Basin (NRB) in Africa were analyzed. Comparison was made between rainfall trend results from the long-term data and those of short-term series selected over different time periods. The bias on trend results from series of short-term records was quantified. Homogeneity test was conducted to assess the coherence of the trend directions on a regional basis. Based on an assumed population (for simplicity) of rainfall data time periods in the range 75–100 years, bias in the short-term trend analysis was noted to reduce by about 10% for every 10% increase in record length. Under some conditions if respected, it was possible to derive trends at stations with short rainfall records based on those at nearby stations with longer term records but in the same region. Using the same data record length and uniform time period at all the selected stations, an improved regional coherence of rainfall trend results was obtained. In the equatorial region, trend in annual rainfall was found mainly positive and significant at level α = 5% in 4 of the 7 stations. Collectively for Sudan, Ethiopia and Egypt, trends in the annual rainfall were mostly negative and significant at α = 5% in 69% of the 32 stations. Heterogeneity in the trend directions for the entire NRB was confirmed at α = 1% in 13% of the 39 stations. These findings are vital for water and agricultural management practices.
Drought is one of the most serious problems arising for human societies and ecosystems from clima... more Drought is one of the most serious problems arising for human societies and ecosystems from climate variability. This phenomenon causes billions of dollars in global damages annually and affects more people than any other form of natural disasters. In this study, the trends of rainfall and meteorological drought time series were investigated at ten stations located in the east of Iran for the period of 1966–2005. Amounts of drought severity were computed using standard precipitation index (SPI) for a 12-month time scale. The trend analyses of the data were also performed using the Mann–Kendall test and the Sen’s slope estimator. The results of this study showed that the rainfall and drought data had high variations to average values in the study period, and these variations increased with increasing aridity towards the east of the study area. The results of the trend tests revealed statistically significant decreasing trends in the rainfall time series of Sar-Pol-Zohab, Bijar, Sanan...
Trends in rainfall at 39 locations of the Nile River Basin (NRB) in Africa were analyzed. Compari... more Trends in rainfall at 39 locations of the Nile River Basin (NRB) in Africa were analyzed. Comparison was made between rainfall trend results from the long-term data and those of short-term series selected over different time periods. The bias on trend results from series of short-term records was quantified. Homogeneity test was conducted to assess the coherence of the trend directions on a regional basis. Based on an assumed population (for simplicity) of rainfall data time periods in the range 75–100 years, bias in the short-term trend analysis was noted to reduce by about 10% for every 10% increase in record length. Under some conditions if respected, it was possible to derive trends at stations with short rainfall records based on those at nearby stations with longer term records but in the same region. Using the same data record length and uniform time period at all the selected stations, an improved regional coherence of rainfall trend results was obtained. In the equatorial region, trend in annual rainfall was found mainly positive and significant at level α = 5% in 4 of the 7 stations. Collectively for Sudan, Ethiopia and Egypt, trends in the annual rainfall were mostly negative and significant at α = 5% in 69% of the 32 stations. Heterogeneity in the trend directions for the entire NRB was confirmed at α = 1% in 13% of the 39 stations. These findings are vital for water and agricultural management practices.
Drought is one of the most serious problems arising for human societies and ecosystems from clima... more Drought is one of the most serious problems arising for human societies and ecosystems from climate variability. This phenomenon causes billions of dollars in global damages annually and affects more people than any other form of natural disasters. In this study, the trends of rainfall and meteorological drought time series were investigated at ten stations located in the east of Iran for the period of 1966–2005. Amounts of drought severity were computed using standard precipitation index (SPI) for a 12-month time scale. The trend analyses of the data were also performed using the Mann–Kendall test and the Sen’s slope estimator. The results of this study showed that the rainfall and drought data had high variations to average values in the study period, and these variations increased with increasing aridity towards the east of the study area. The results of the trend tests revealed statistically significant decreasing trends in the rainfall time series of Sar-Pol-Zohab, Bijar, Sanan...
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Papers by Hossein Tabari