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Anomalous moisture sources of the Rhine basin during the extremely dry summers of 2003 and 2018
Weather and Climate Extremes ( IF 8 ) Pub Date : 2020-12-29 , DOI: 10.1016/j.wace.2020.100302
Imme Benedict , Chiel C. van Heerwaarden , Eveline C. van der Linden , Albrecht H. Weerts , Wilco Hazeleger

Droughts can be studied from an atmospheric perspective by analysing large-scale dynamics and thermodynamics, and from a hydrological perspective by analysing interaction of precipitation, evaporation, soil moisture and temperature at the land-surface. Here, we study it from both perspectives, and assess the moisture (evaporative) sources of precipitation in the Rhine basin during the exceptionally dry summers of 2003 and 2018. We use ERA5 re-analysis data (1979–2018) and the Eulerian moisture tracking model WAM-2layers in order to determine the moisture sources of the Rhine basin. During an average summer, these evaporative sources are mostly located over the Atlantic Ocean, and there is a large contribution from continental evaporation, mostly from regions west of the Rhine basin. Both in 2003 and 2018 the absolute moisture source contribution declined over the ocean. In both years the anomalous moisture fluxes over the boundaries of the Rhine basin are mainly a result of anomalous wind and not because of anomalous moisture advection by the mean wind. Due to high pressure (blocking) over Europe, moisture is transported from the ocean with anticyclonic flow around the Rhine basin, but not into the basin. In 2018, unlike 2003, moisture is transported from the east towards the basin as a result of the anticyclonic flow around the Scandinavian blocking. The large-scale synoptic situation during the summer of 2018 was exceptional, and very favourable for dry conditions over the Rhine basin. Although blocking also occurred in 2003, the exact synoptic conditions were less favourable to dryness over the Rhine basin. In 2003 however, the recycling of moisture within the basin was much lower than the climatology and 2018, especially in August, possibly indicating the drying out of the soil resulting in the second heatwave in August 2003. To conclude, although the summer of 2003 and 2018 were both exceptionally dry, their characteristics in terms of moisture sources and recycling, and thereby their dependence on the large-scale circulation and land-atmosphere interactions, were found to be very different. It is therefore imperative that droughts are also studied as individual events to advance understanding of complex interactions between the large-scale atmospheric processes and the land surface.



中文翻译:

2003年和2018年极端干旱的夏季,莱茵河流域的异常水分源

可以通过分析大规模的动力学和热力学从大气的角度研究干旱,而通过分析陆地表面的降水,蒸发,土壤水分和温度的相互作用从水文的角度研究干旱。在这里,我们从两个角度进行研究,并评估了2003年和2018年异常干燥的夏季莱茵河流域的降水(蒸发)降水源。我们使用ERA5重新分析数据(1979-2018年)和欧拉湿度跟踪为了确定莱茵盆地的水分来源,对WAM-2layers进行了建模。在通常的夏季,这些蒸发源主要位于大西洋上空,大陆蒸发的贡献很大,主要来自莱茵河流域以西的地区。2003年和2018年,海洋中绝对水分源的贡献均下降。在这两年中,莱茵河流域边界上的异常水汽通量主要是由于风的异常引起,而不是由于平均风对流的异常对流。由于欧洲的高压(阻塞),水分以反旋流的形式从海洋中输送到莱茵河盆地周围,但没有进入盆地。与2003年不同,2018年,由于斯堪的纳维亚阻塞周围的反气旋气流,水分从东部流向盆地。2018年夏季的大范围天气情况异常特殊,非常适合莱茵河流域的干旱条件。尽管在2003年也发生了阻塞,但确切的天气条件不利于莱茵河流域的干旱。然而,在2003年,流域内的水分再循环远低于气候和2018年,特别是在8月,这可能表明土壤干drying,导致了2003年8月的第二次热浪。总之,尽管2003年夏天和2004年, 2018年都异常干燥,其在水分来源和循环利用方面的特点非常不同,因此它们对大规模循环和陆地-大气相互作用的依赖也很大。因此,必须将干旱作为单独的事件进行研究,以加深对大规模大气过程与陆地表面之间复杂相互作用的理解。可能表明土壤干drying,导致了2003年8月的第二次热浪。总而言之,尽管2003年和2018年夏天都异常干燥,但它们在水分来源和循环利用方面的特点,因此它们依赖于发现尺度环流和土地-大气相互作用是非常不同的。因此,必须将干旱作为单个事件进行研究,以加深对大规模大气过程与陆地表面之间复杂相互作用的理解。可能表明土壤干drying,导致了2003年8月的第二次热浪。总而言之,尽管2003年和2018年夏天都异常干燥,但是它们在水分来源和循环利用方面的特性,因此它们依赖于大量的发现规模尺度环流和陆地-大气相互作用是非常不同的。因此,必须将干旱作为单个事件进行研究,以加深对大规模大气过程与陆地表面之间复杂相互作用的理解。被发现是非常不同的。因此,必须将干旱作为单个事件进行研究,以加深对大规模大气过程与陆地表面之间复杂相互作用的理解。被发现是非常不同的。因此,必须将干旱作为单个事件进行研究,以加深对大规模大气过程与陆地表面之间复杂相互作用的理解。

更新日期:2021-01-29
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