Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensembl...Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensemble Empirical Mode Decomposition. The study was based on a homogenized daily surface air temperature （SAT） dataset for the period 1955–2003. The annual cycle here is referred to as a refined modulated annual cycle （MAC）. The results show that spring at Beijing has arrived significantly earlier by about 2.98 d （10 yr）-1, of which about 1.85 d （10 yr）-1 is due to changes in the annual cycle and 1.13 d （10 yr）-1 due to the long-term warming trend. Variations in the MAC component explain about 92.5% of the total variance in the Beijing daily SAT series and could cause as much as a 20-day shift in the onset of spring from one year to another. The onset of spring has been advancing all over northern China, but more significant in the east than in the west part of the region. These differences are somehow unexplainable by the zonal pattern of the warming trend over the whole region, but can be explained by opposite changes in the spring phase of the MAC, i.e. advancing in the east while delaying in the west. In the east of northern China, the change in the spring phase of MAC explains 40%–60% of the spring onset trend and is attributable to a weakening Asian winter monsoon. The average sea level pressure in Siberia （55°–80°N, 50°–110°E）, an index of the strength of the winter monsoon, could serve as a potential short-term predictor for the onset of spring in the east of northern China.展开更多
Variability of wintertime surface air temperature (SAT) in the Kingdom of Saudi Arabia (KSA) is studied. The study is based on time series over thirty one years in length (1978-2008). For the analysis, we use the coef...Variability of wintertime surface air temperature (SAT) in the Kingdom of Saudi Arabia (KSA) is studied. The study is based on time series over thirty one years in length (1978-2008). For the analysis, we use the coefficient of variability (COV) Mann-Kendal statistical test, running mean and cumulative annual mean (CAM). The coefficient of variability (COV) for wintertime SAT decreases gradually from the north to the south of KSA. The higher values for COV occur in northern and northeastern KSA;there are due to the effect of the traveling Mediterranean depressions and their interaction with the inverted-V shape trough of the Sudan low. The relationship between COV and latitude is highly significant, while with longitude it is not significant. The Mann-Kendal statistical test illustrates that positive trends (warming) in wintertime SAT series occurs over the all stations, and that the trends are significant at middle and southern regions of KSA. Recent warming has only occurred during the last two decades at most stations. While cooling in the wintertime SAT appears for the short period of about 5 years, 1978-1983 and 1988-1992. These trends are consistence with trends in the global mean SAT. The results obtained from CAW lead to the conclusion that the thermic regime is modifying in the KSA. This dramatic enhancement, occurred at the beginning of the year 1993, is reflected in net modification in the SAT time series. The analysis of the SAT also shows a significant warming trend after the year 1997 with a rate of 0.03?C/year.展开更多
The research on the characteristic frequency of precipitation is a great significance for guiding regional agricultural planning, water conservancy project designs, and drought and flood control. Droughts and floods o...The research on the characteristic frequency of precipitation is a great significance for guiding regional agricultural planning, water conservancy project designs, and drought and flood control. Droughts and floods occurred in northern Weihe Loess Plateau, affecting growing and yield of winter wheat in the area. Based on the daily precipitation data of 29 meteorological stations from 1981 to 2012, this study is to address the analysis of three different frequencies of annual precipitation at 5%, 50%, and 95%, and to determine the amount of rainfall excess and water shortage during seven growth stages of winter wheat at 5%, 10%, and 20% frequencies, respectively. Pearson type III curve was selected for this study to analyze the distribution frequency of annual rainfall and rainfall amount following seven growth stages of winter wheat crop in 29 stations of Northern Weihe loess plateau. As a result of our study, annual precipitation is gradually increasing from southwest to northeast of Northern Weihe loess plateau. The highest amount of annual precipitation occurred in the Baoji area and the lowest precipitation covered by the northwest area of Northern Weihe loess plateau. Moreover, the amount of rainfall of seven growth stages indicates that excessive rainfall occurs not only in the first stage (sowing to tillering) and seventh stage (flowering to ripening) but also in second stage (tillering to wintering). In the seventh stage, a large amount of excessive rainfall occurred in Changwu, Bin, Qianyang, Fengxiang, Baojiqu, and Baojixian. Moreover, water shortage is distributed in the third stage (from wintering to greening), the fourth stage (from greening to jointing), the fifth stage (from jointing to heading), and the sixth stage (from heading to flowering). Furthermore, the worst water shortages occurred in Hancheng, Heyang, Chengcheng, Pucheng, Dali, Tongchuan, and Fuping in the fourth stage (greening to jointing stage). Even though we study the crop water requirement under extreme rainfall conditions, the amount of rainwater still supply inadequate in some parts of the winter wheat growth stage. Therefore, this study provides main clues for the next step to study the irrigation water needs of winter wheat crops and to reduce agricultural risks in 29 counties in the northern loess plateau and other regions.展开更多
基金sponsored by the National Basic Research Program of China(Grant Nos. 2011CB952000, 2006CB400504)the Na-tional Natural Science Foundation of China (Grant No.41005039)+1 种基金Wu was sponsored by the National Science Foundation of USA (ATM-0917743)Yan was sponsored by the National Basic Research Program of China(Grant No. 2009CB421401)
文摘Climatic changes in the onset of spring in northern China associated with changes in the annual cycle and with a recent warming trend were quantified using a recently developed adaptive data analysis tool, the Ensemble Empirical Mode Decomposition. The study was based on a homogenized daily surface air temperature （SAT） dataset for the period 1955–2003. The annual cycle here is referred to as a refined modulated annual cycle （MAC）. The results show that spring at Beijing has arrived significantly earlier by about 2.98 d （10 yr）-1, of which about 1.85 d （10 yr）-1 is due to changes in the annual cycle and 1.13 d （10 yr）-1 due to the long-term warming trend. Variations in the MAC component explain about 92.5% of the total variance in the Beijing daily SAT series and could cause as much as a 20-day shift in the onset of spring from one year to another. The onset of spring has been advancing all over northern China, but more significant in the east than in the west part of the region. These differences are somehow unexplainable by the zonal pattern of the warming trend over the whole region, but can be explained by opposite changes in the spring phase of the MAC, i.e. advancing in the east while delaying in the west. In the east of northern China, the change in the spring phase of MAC explains 40%–60% of the spring onset trend and is attributable to a weakening Asian winter monsoon. The average sea level pressure in Siberia （55°–80°N, 50°–110°E）, an index of the strength of the winter monsoon, could serve as a potential short-term predictor for the onset of spring in the east of northern China.
文摘Variability of wintertime surface air temperature (SAT) in the Kingdom of Saudi Arabia (KSA) is studied. The study is based on time series over thirty one years in length (1978-2008). For the analysis, we use the coefficient of variability (COV) Mann-Kendal statistical test, running mean and cumulative annual mean (CAM). The coefficient of variability (COV) for wintertime SAT decreases gradually from the north to the south of KSA. The higher values for COV occur in northern and northeastern KSA;there are due to the effect of the traveling Mediterranean depressions and their interaction with the inverted-V shape trough of the Sudan low. The relationship between COV and latitude is highly significant, while with longitude it is not significant. The Mann-Kendal statistical test illustrates that positive trends (warming) in wintertime SAT series occurs over the all stations, and that the trends are significant at middle and southern regions of KSA. Recent warming has only occurred during the last two decades at most stations. While cooling in the wintertime SAT appears for the short period of about 5 years, 1978-1983 and 1988-1992. These trends are consistence with trends in the global mean SAT. The results obtained from CAW lead to the conclusion that the thermic regime is modifying in the KSA. This dramatic enhancement, occurred at the beginning of the year 1993, is reflected in net modification in the SAT time series. The analysis of the SAT also shows a significant warming trend after the year 1997 with a rate of 0.03?C/year.
文摘The research on the characteristic frequency of precipitation is a great significance for guiding regional agricultural planning, water conservancy project designs, and drought and flood control. Droughts and floods occurred in northern Weihe Loess Plateau, affecting growing and yield of winter wheat in the area. Based on the daily precipitation data of 29 meteorological stations from 1981 to 2012, this study is to address the analysis of three different frequencies of annual precipitation at 5%, 50%, and 95%, and to determine the amount of rainfall excess and water shortage during seven growth stages of winter wheat at 5%, 10%, and 20% frequencies, respectively. Pearson type III curve was selected for this study to analyze the distribution frequency of annual rainfall and rainfall amount following seven growth stages of winter wheat crop in 29 stations of Northern Weihe loess plateau. As a result of our study, annual precipitation is gradually increasing from southwest to northeast of Northern Weihe loess plateau. The highest amount of annual precipitation occurred in the Baoji area and the lowest precipitation covered by the northwest area of Northern Weihe loess plateau. Moreover, the amount of rainfall of seven growth stages indicates that excessive rainfall occurs not only in the first stage (sowing to tillering) and seventh stage (flowering to ripening) but also in second stage (tillering to wintering). In the seventh stage, a large amount of excessive rainfall occurred in Changwu, Bin, Qianyang, Fengxiang, Baojiqu, and Baojixian. Moreover, water shortage is distributed in the third stage (from wintering to greening), the fourth stage (from greening to jointing), the fifth stage (from jointing to heading), and the sixth stage (from heading to flowering). Furthermore, the worst water shortages occurred in Hancheng, Heyang, Chengcheng, Pucheng, Dali, Tongchuan, and Fuping in the fourth stage (greening to jointing stage). Even though we study the crop water requirement under extreme rainfall conditions, the amount of rainwater still supply inadequate in some parts of the winter wheat growth stage. Therefore, this study provides main clues for the next step to study the irrigation water needs of winter wheat crops and to reduce agricultural risks in 29 counties in the northern loess plateau and other regions.
