Part of the sandization process in southwestern Rio Grande do Sul (Brazil) originates from daily torrential rains. However, it is believed that climate changes have been provoking more frequent and more intense rains ...Part of the sandization process in southwestern Rio Grande do Sul (Brazil) originates from daily torrential rains. However, it is believed that climate changes have been provoking more frequent and more intense rains in the region, a phenomenon which can change the dynamic of erosion/transport/sedimentation natural processes. The objective of this work is to identify the behavior of daily rainfall extreme events (in terms of their frequency, return time, tendency and genesis), relating them to both climatic change issue and enhancement of erosive processes. We have used daily rainfall data from meteorology stations of Brazilian National Water Agency (ANA) for the period between 1928 and 2017 and the percentile 99 was used to identify daily rainfall extreme value (71.5 mm). The upper values were categorized and their absolute and relative frequencies as well as their return time were identified. The temporal tendency of these events was evaluated by the Mann-Kendall test, considering the 90 years of the series. The results showed that there was a significant increase in heavy rainfall events in November and December in the last two decades and that the return time for these events decreased throughout the time. Synoptic analyses from GOES 13 satellite infrared imagery and from ECMWF/ERA/Interim reanalysis data allowed concluding that such intense rainfall events originated themselves from the transport of moisture from the Amazon by Low-Level Jets, which promoted the formation of Mesoscale Convective Complex, with large volumes of rain in the study region. Thus, the recurrence of these events in the southwest of Rio Grande do Sul may intensify these sandization processes, since they arise from the association between natural morphoscultural dynamics and agricultural practices, generating environmental problems for the region.展开更多
利用常规气象观测资料、降雪加密观测资料和NCEP的1°×1°再分析资料,对2009年11月10—12日和2011年11月29—30日河北省南部两次回流暴雪天气过程进行对比分析。结果表明:河北省南部两次回流暴雪的时空分布具有中尺度特征...利用常规气象观测资料、降雪加密观测资料和NCEP的1°×1°再分析资料,对2009年11月10—12日和2011年11月29—30日河北省南部两次回流暴雪天气过程进行对比分析。结果表明:河北省南部两次回流暴雪的时空分布具有中尺度特征。两次回流暴雪的典型天气形势为500 h Pa高空河套地区有低压槽东移,700 h Pa有切变线影响,地面蒙古冷高压东移至东北地区南下,河套倒槽发展,华北地面为东高西低形势。回流暴雪过程中高低空急流有非常重要的作用,冷空气自850 h Pa以下随强劲的东北风回流至河北省南部形成冷垫,700 h Pa暖湿气流随西南急流输送至河北省南部叠加在冷垫上辐合抬升,高空200 h Pa急流右后侧的辐散抽吸作用使上升运动加强。华北平原高空存在一支垂直环流,边界层东北风到达太行山东麓,在迎风坡抬升至对流层中高层转为西南风,到达东北地区转为下沉气流,再与低层东北风构成一个完整的垂直环流。θse密集区由地面向上向北伸展至700 h Pa,锋面结构特征明显,锋面的前沿从北向南推进,地面锋面附近850 h Pa以下等θse线与地面垂直,具有对流中性层结。回流强降雪发生在地面锋后冷气团中。展开更多
文摘Part of the sandization process in southwestern Rio Grande do Sul (Brazil) originates from daily torrential rains. However, it is believed that climate changes have been provoking more frequent and more intense rains in the region, a phenomenon which can change the dynamic of erosion/transport/sedimentation natural processes. The objective of this work is to identify the behavior of daily rainfall extreme events (in terms of their frequency, return time, tendency and genesis), relating them to both climatic change issue and enhancement of erosive processes. We have used daily rainfall data from meteorology stations of Brazilian National Water Agency (ANA) for the period between 1928 and 2017 and the percentile 99 was used to identify daily rainfall extreme value (71.5 mm). The upper values were categorized and their absolute and relative frequencies as well as their return time were identified. The temporal tendency of these events was evaluated by the Mann-Kendall test, considering the 90 years of the series. The results showed that there was a significant increase in heavy rainfall events in November and December in the last two decades and that the return time for these events decreased throughout the time. Synoptic analyses from GOES 13 satellite infrared imagery and from ECMWF/ERA/Interim reanalysis data allowed concluding that such intense rainfall events originated themselves from the transport of moisture from the Amazon by Low-Level Jets, which promoted the formation of Mesoscale Convective Complex, with large volumes of rain in the study region. Thus, the recurrence of these events in the southwest of Rio Grande do Sul may intensify these sandization processes, since they arise from the association between natural morphoscultural dynamics and agricultural practices, generating environmental problems for the region.
文摘利用常规气象观测资料、降雪加密观测资料和NCEP的1°×1°再分析资料,对2009年11月10—12日和2011年11月29—30日河北省南部两次回流暴雪天气过程进行对比分析。结果表明:河北省南部两次回流暴雪的时空分布具有中尺度特征。两次回流暴雪的典型天气形势为500 h Pa高空河套地区有低压槽东移,700 h Pa有切变线影响,地面蒙古冷高压东移至东北地区南下,河套倒槽发展,华北地面为东高西低形势。回流暴雪过程中高低空急流有非常重要的作用,冷空气自850 h Pa以下随强劲的东北风回流至河北省南部形成冷垫,700 h Pa暖湿气流随西南急流输送至河北省南部叠加在冷垫上辐合抬升,高空200 h Pa急流右后侧的辐散抽吸作用使上升运动加强。华北平原高空存在一支垂直环流,边界层东北风到达太行山东麓,在迎风坡抬升至对流层中高层转为西南风,到达东北地区转为下沉气流,再与低层东北风构成一个完整的垂直环流。θse密集区由地面向上向北伸展至700 h Pa,锋面结构特征明显,锋面的前沿从北向南推进,地面锋面附近850 h Pa以下等θse线与地面垂直,具有对流中性层结。回流强降雪发生在地面锋后冷气团中。
