Extreme Heavy Rainfall Research Articles

Oscillation characteristics of summer precipitation in the Huaihe River valley and relevant climate background

Based on the summer precipitation data from the Huaihe River valley and the middle and lower reaches of the Yangtze River from 1922 to 2007, we analyzed the interannual and interdecadal oscillation and probability distribution characteristics of summer precipitation in the Huaihe River valley during the same period, using the wavelet transform and generalized extreme distribution methods. Whereby, we studied the climate background of East Asia Summer Monsoon (EASM), Sea Surface Temperature (SST), East Asia telecorrelation circulation, and their relationship with the interannual and interdecadal oscillation of summer precipitation in the Huaihe River valley. We further compared the difference of interdecadal oscillation of summer precipitation and the relevant climate background between the Huaihe River valley and the middle and lower reaches of the Yangtze River. The results show that: 1) The intensity change of quasi-biennial oscillation (QBO) of summer precipitation in the Huaihe River valley is consistent with that of interdecadal oscillation. The summer precipitation in the Huaihe River valley has been more than normal since the end of the 1990s, and the QBO is very significant. Meanwhile, the probability of occurrence of extreme heavy rainfall increased obviously. 2) The interdecadal oscillation of summer precipitation in the Huaihe River valley has a close relationship with the Pacific Decadal Oscillation (PDO) and interdecadal oscillation of EASM. When PDO is in the cold phase and EASM weakens, the summer precipitation will be greater than normal. 3) QBO of summer precipitation in the Huaihe River valley is mainly controlled by that of EASM, and it has a relationship with a circulation pattern of “positive-negative-positive” from the high to the low latitudes in East Asia. 4) There is interdecadal phase difference in summer precipitation between the Huaihe River valley and the middle and the lower reaches of the Yangtze River, which is mainly related to the intensity and position of West Pacific subtropical high.

A Modified Kain–Fritsch Scheme and Its Application for the Simulation of an Extreme Precipitation Event in Vietnam

Abstract From 24 to 26 November 2004, an extreme heavy rainfall event occurred in the mountainous provinces of central Vietnam, resulting in severe flooding along local rivers. The Regional Atmospheric Modeling System, version 4.4, is used to simulate this event. In the present study, the convective parameterization scheme includes the original Kain–Fritsch scheme and a modified one in which a new diagnostic equation to compute updraft velocity, closure assumption, and trigger function are developed. These modifications take the vertical gradient of the Exner function perturbation into account, with an on–off coefficient to account for the role of the advective terms. According to the event simulations, the simulated precipitation shows that the modified scheme with the new trigger function gives much better results than the original one. Moreover, the interaction between convection and the larger-scale environment is much stronger near the midtroposphere where the return flow associated with lower-level winter monsoon originates. As a result, the modified scheme produces larger and deeper stratiform clouds and leads to a significant amount of resolvable precipitation. On the contrary, the resolvable precipitation is small when the original scheme is used. The improvement in the simulated precipitation is caused by a more explicit physical mechanism of the new trigger function and suggests that the trigger function needs to be developed along with other components of the scheme, such as closure assumption and cloud model, as a whole. The formalistic inclusion of the advective terms in the new equation gives almost no additional improvement of the simulated precipitation.

Geomorphological hazards and monitoring activity along the western rocky coast of the Portofino Promontory (Italy)

The results of geomorphological studies and monitoring activity conducted in the western sector of the Portofino Promontory are presented here. This sector is characterized by numerous, extensive landslide masses and there is evidence of their reactivation during the last century. The instability phenomena can be attributed to landslides with complex kinematics classifiable as rock slump and rock topple, rock slide and rock fall, and rock fall and rock flow. They have involved hamlets and communication routes, with observable damage to man-made structures and terraced agricultural terrain, including collapses and deformations of the dry-stone walls. The geomorphological surveys, the boreholes and the monitoring activity have shown that several landslides are active, with movement rates of some cm/year. With the presence of predisposing factors relating to the structural lithology and geomorphology of the rocky slopes, the triggering causes of the gravitational movements are attributable to extreme heavy rainfall and to wave cutting, often with concomitant action on the part of both. The study offers a contribution to encourage concrete efforts to continue the monitoring of this area; the overall objective would entail the planning of general stabilization measures, or at least measures to reduce evident geomorphological risks, also taking into account the remarkable environmental value and qualities of this coastal sector.

Effects of Extreme Heavy Rainfall in the Troposphere on the Ionosphere

研究气象活动对电离层变化的影响.利用时序叠加方法,通过对1958-1998年期间发生在武汉的5次特大暴雨天气事件对武汉上空电离层变化的影响进行分析,发现:(1)特大暴雨能够引起低电离层fbEs和f0Es参量较明显地减小;(2)特大暴雨对电离层F区寻常波描迹的最低虚高h'F和电离层等效峰高hpF的参量也有一定影响,且随着雨量的增大这种影响作用也会增加;(3)特大暴雨对电离层其他参量影响甚弱或没有影响.本文认为,特大暴雨天气事件对电离层的影响主要来自于动力过程,特别是特大暴雨激发的或相伴的大气重力波、潮汐波和行星波等长周期大尺度过程的作用.

HEAVY RAINFALL DISTRIBUTIONS BY SEASON IN LOUISIANA: SYNOPTIC INTERPRETATIONS AND QUANTILE ESTIMATES1

ABSTRACT: In most studies, quantile estimates of extreme 24‐hour rainfall are given in annual probabilities. The probability of experiencing an excessive storm event, however, differs throughout the year. As a result, this paper explored the differences between heavy rainfall distributions by season in Louisiana. It was concluded by using the Kruskal‐Wallis and Mann‐Whitney tests that the distribution of heavy rainfall events differs significantly between particular seasons at the sites near the Gulf Coast. Furthermore, seasonal frequency curves varied dramatically at the four sites examined. Mixed distributions within these data were not found to be problematic, but the mechanisms that produced the events were found to change seasonally. Extreme heavy rainfall events in winter and spring were primarily generated by frontal weather systems, while summer and fall events had high proportions of events produced by tropical disturbances and airmass (free‐convective) conditions.

梅雨期の豪雨帯へ南側面から流入する水蒸気流束

梅雨期の豪雨帯へ南側面から流入する水蒸気流束