Precipitation Concentration Period Research Articles

近50年黄河上中游降水多时间尺度特征分析

利用1961~2011年黄河上中游45站年、月降水量资料，通过计算气候倾向率、降水指数γ、降水集中度和集中期等，对该区降水年际变化和年内分配特征及其演变趋势进行诊断分析。结果表明：1) 黄河上中游区年降水量自东南向西北迅速递减，并且存在两个降水变化敏感区：黄河源区和陇中–陇东黄土高原区。黄河源区年降水量呈增加趋势，而陇中–陇东黄土高原区干旱化趋势明显。2) 400 mm等值线在黄河源区与黄河中游区的移动趋势和轨迹存在明显差异。黄河源区该线总体呈向北移动的趋势；黄河中游区2000年以前该线向东南方向移动的趋势显著，2000年以后则向西北方向回归。3) 黄河上中游降水季节分配变化趋势总体为春、夏季降水明显减少，而秋季降水显著增多，特别是2000年之后。而不同区域各季降水的变化趋势不尽相同，关中平原是降水季节分配变化最明显的区域。4) 黄河上中游区降水集中期总体都在7月，黄河源区集中期略早于黄河中游地区。降水集中度由东南向西北递增。全区集中度在1998年以前年际波动较大，1998年以后趋于稳定且接近均值。Based on the yearly and monthly precipitation data of 45 stations from 1961 to 2011 over the up-per and middle reach of Yellow River (UMRYR), by the method of climate tendency rate, precipita-tion index, concentration degree and period, the precipitation interannual variation and distribu-tion characteristic and its evolution trend were analyzed. The results show that: 1) The annual precipitation rapidly declines from southeast to northwest, and there was a rain shadow area from Lanzhou to Huining of middle Gansu province. The two climate change sensitive areas were source area of the Yellow River and middle and east of Gansu loess plateau. The precipitation increased in source area of the Yellow River, mean value of climate tendency rate was 9.5 mm/10a. The drought trend was obvious in middle and east of Gansu loess plateau, average value of climate tendency rate was -23.4 mm/10a. 2) There were significant difference of mobile trend and track of 400 mm rainfall contour between source area and middle reach of the Yellow River. In source area of the Yellow River, the trend of 400 mm rainfall contour moved north, but in middle reach of the Yellow River the contour obvious moved southeast before 2000, and regressed to northwest after 2000. 3) The general variation trend of seasonal distribution of precipitation in UMRYR were that the precipitation reduced obviously in spring and summer but increased significantly in autumn, especially after 2000. The variation trend of precipitation in each season was inconsistent in different areas, and the area where seasonal distribution of precipitation was obvious was Gu-anzhong plain. 4) The precipitation concentration period of UMRYR was in July, but concentration period of source area was slightly earlier than middle reach of the Yellow River. The precipitation concentration degree increased from southeast to northwest, and the value was between 0.45 - 0.71.

Characterizing the changing behaviours of precipitation concentration in the Yangtze River Basin, China

AbstractThe statistical characteristics of precipitation on the daily resolution play an important role not only in the risk assessment of floods and droughts but also in the land use management. In this study, spatial and temporal patterns of the precipitation concentration in the Yangtze River Basin are investigated by using three indices, i.e. precipitation concentration index (CI), precipitation concentration degree (PCD) and precipitation concentration period (PCP). Based on meteorological data of 147 stations for the period of 1960–2008, non‐parametric trend analysis and wavelet transformation analysis are employed to detect the temporal variation of these indices. Spatial variability of precipitation concentration indices and their trends are analysed and demonstrated with the help of GIS tools. The results indicate the following: (i) The high precipitation CI values mainly distribute in the middle region of the Yangtze River Basin, whereas the lower and lowest CI values are found in the lower and upper regions, respectively. A roughly east–west gradient for PCD value and PCP value varies from 0.26 to 0.77 and from 123 to 197, respectively. (ii) The analysis results of precipitation CI trends for different periods (i.e. recent 40, 30 and 20 years) show that the middle region of the Yangtze River Basin experienced a transition from decreasing precipitation CI to increasing precipitation CI during the last two decades, although the decreasing long‐term trends in the precipitation CI are not significant in most areas during the period of 1960–2008. (iii) The upper basin, middle basin and lower basin are, respectively, dominated by the significant decreasing, increasing and no significant trends in PCD. A dominance of insignificant PCP trends is observed in the entire basin during 1960–2008 despite that a few areas in the upper region are characterized by significant decreasing trends. (iv) Interdecadal oscillations can be found for three precipitation indices, but with no constant periodicity. Furthermore, good positive correlations have been detected between precipitation CI and PCD, whereas insignificant correlation coefficients of PCP with precipitation are common in the basin. The results can provide beneficial reference to water resource and eco‐environment and mitigation to flood or drought hazards in the Yangtze River Basin for policymakers and stakeholders. Copyright © 2012 John Wiley & Sons, Ltd.

The heterogeneity of Meiyu rainfall over Yangtze–Huaihe River valley and its relationship with oceanic surface heating and intraseasonal variability

Increasing heavy concentrated Meiyu precipitation over the Yangtze–Huaihe river valley (YHRV) during recent years has been previously reported. In fact, the concentrated Meiyu rainfall occurring in a small region or a certain period easily results in floods, thus it is worthy to analyze the heterogeneity of Meiyu rainfall over YHRV. In this study, we use both of precipitation concentration period (PCP) and precipitation concentration degree (PCD) based on vector analysis to identify the heterogeneity of Meiyu rainfall over YHRV. On the climatological mean, the concentrated heavy precipitation occurs in late summer over the Yangtze River Delta, where is usually suffered by floods. The dominant two patterns of PCP and PCD variations are northeast–southwest dipole pattern, homogeneous anomalies and homogeneous variation, north–south dipole pattern, respectively. In addition, the relationship on heterogeneity of Meiyu rainfall with sea surface temperature (SST) and the low level summer intraseasonal oscillation (ISO) are investigated. Two key regions of SST activities are found: Bay of Bengal (BOB) and Equatorial eastern Pacific. From BOB, more abundant water vapor has been brought. On the El Nino-Southern Oscillation variation, it is closely relative with PCD–PC1 during the decaying phase of El Nino, while PCP–PC2 is accompanied with developing phase of La Nina events, suggesting a negative feedback of PCP–PC2 on the Nino3.4 SST, and changes to positive during the later winter. On the ISO activities, the robust regions are located over the high-latitude areas, which are closely related with northeastern cold vortex. The north “cold and dry” air southwardly invaded with the lower-level strong warm air in the rainy area, and easily formed an “upper-wet and lower-dry” unstable layer. Under the trigger of the upward motion, the concentrated heavy rainfall easily occurred over YHRV. In all, the homogeneity variation of the concentrated heavy precipitation over YHRV is closely associated with both of the heating forcing (SST) and dynamical atmospheric forcing (low-level ISO).

Spatial and temporal variability of precipitation concentration index, concentration degree and concentration period in Xinjiang, China

AbstractThis paper studied the spatial and temporal variability of the statistical structures of precipitation across Xinjiang, China, by analysing the time series of daily precipitation from 50 weather stations during the period from 1961 to 2008. Three indices precipitation concentration index (CI), precipitation concentration degree (PCD) and precipitation concentration period (PCP) were used to detect precipitation concentrations and the associated spatial patterns. The results show that higher precipitation CI values were mainly observed in Southern Xinjiang, whereas lower precipitation CI values were mostly detected in Northern Xinjiang. The precipitation CI values are noticeably larger in places where both annual total precipitation and number of rainy days are lower. The Mann–Kendall trend test demonstrates that the most parts of Xinjiang are characterized by no significant trends of precipitation CI at the 0.05 significance level. The periodicity characteristic of precipitation CI time series in Xinjiang could be detected by wavelet power spectrum analysis, and significant periods of that in most of Xinjiang were concentrated on 2–5 years band. The results of PCP reveal that rainfall in Xinjiang mostly occurs in summer, and the rainy season arrives earlier in Eastern Xinjiang than Western Xinjiang, whereas the results of PCD indicate that the rainfall in Northern Xinjiang was more dispersed within a year than that in Southern Xinjiang. Copyright © 2010 Royal Meteorological Society

Climatic trends of different intensity heavy precipitation events concentration in China

Based on 740 stations of daily precipitation datasets in China, the precipitationconcentration degree (PCD) and precipitation-concentration period (PCP) of different intensity durative precipitation events were calculated to analyze their statistical characteristics, mainly including spatial and temporal distributions, variations and climatic trends of the two parameters of the durative heavy precipitation events in China. It is proved that these two parameters of heavy rainfall can display the temporal inhomogeneity in the precipitation field. And it is also found that there is a good positive relationship between the precipitation-concentration degree and annual rainfall amount in the Eastern and Central China. This method can be applied in flood assessment and climate change fields.

A Study on the Feature of Precipitation Concentration and Its Relation to Flood‐Producing in the Yangtze River Valley of China

AbstractBased on the precipitation concentration degree (PCD) and precipitation concentration period (PCP), we analyze the characteristics of spatial and temporal distribution and variation of precipitation in the Yangtze River Valley. It is proved that these two parameters can display the temporal inhomogeneity in the precipitation field, and pick up the corresponding period of the largest precipitation amount in theoretical analysis of floods and droughts in the Yangtze River Valley. Thus the basic characteristics and mechanism of flood and drought can be fairly analyzed. And it is also found that there is a good relationship between the PCD and the East Asian monsoon index in the middle and lower reaches of the Yangtze River.