Farmers' first rain: investigating dry season rainfall characteristics in the Peruvian Andes
Farmers' first rain: investigating dry season rainfall characteristics in the Peruvian Andes
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农民的第一场雨：调查秘鲁安第斯山脉的旱季降雨特征
DOI：
10.1088/2515-7620/ace516
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发表时间：
2023
影响因子：
2.9
通讯作者：
Klein C
中科院分区：
文献类型：
--
作者：
Klein C
在秘鲁安第斯山脉，8月至9月旱季结束时的第一场小雨被称为“pushpa”。这些降雨软化了土壤，改善了播种条件，对种植日期和农业规划至关重要。然而，迄今为止，普什帕在文学中仍未被探索。本研究使用观测资料和允许对流的模式模拟来描述秘鲁里约热内卢Santa山谷的pushpa特征。将2018年8月观测到的普什巴现象与同一季节的干湿事件进行比较，我们发现普什巴现象与高层西风相吻合，而高层西风是干旱时期的特征。这些条件造成了上层干燥层，有利于小规模的垂直顶对流，解释了据报道普什帕典型的低降雨强度。气候学上，我们发现83%的普什帕型事件发生在西风下，主要发生在8月份，此时60%的模拟空间降雨范围与普什帕有关。9月，更大、更强烈的深层对流事件随着偏东风逐渐增加，导致相对推送云覆盖率下降到20%。我们注意到，在关键播种期，2000-2009年的pushpa和强对流降雨类型之间的平衡具有很高的年际和年代际变化，pushpa降雨的空间范围是2010-2018年十年的两倍。这一结果可能解释了圣塔山谷农民的看法，他们最近报告说，由于雨季开始前的pushpa降雨延迟但更强烈，他们面临的挑战增加了。因此，我们认为播种和发芽季节受到pushpa型和深度对流降雨平衡的关键影响，导致晚初雨更强的可能性更高。
In the Peruvian Andes, the first light rainfalls towards the end of the dry season in August-September are known as pushpa. Softening soils and improving sowing conditions, these rains are crucial for planting dates and agricultural planning. Yet pushpa remains to date unexplored in the literature. This study uses observations and convection-permitting model simulations to describe the characteristics of pushpa in the Rio Santa valley (Peru). Comparing an observed pushpa case in August 2018 with a dry and wet event of the same season, we find pushpa to coincide with upper-level westerly winds that are otherwise characteristic for dry periods. These conditions impose an upper-level dry layer that favours small-scale, vertically-capped convection, explaining the low rainfall intensities that are reportedly typical for pushpa. Climatologically, we find 83% of pushpa-type events to occur under westerly winds, dominating in August, when 60% of the modelled spatial rainfall extent is linked to pushpa. Larger, more intense deep-convective events gradually increase alongside more easterly winds in September, causing the relative pushpa cloud coverage to drop to ̃20%. We note high inter-annual and-decadal variability in this balance between pushpa and intense convective rainfall types, with the spatial extent of pushpa rainfall being twice as high during 2000-2009 than for the 2010-2018 decade over the key sowing period. This result may explain farmers' perception in the Rio Santa valley, who recently reported increased challenges due to delayed but more intense pushpa rains before the rainy season start. We thus conclude that the sowing and germination season is crucially affected by the balance of pushpa-type and deep-convective rain, resulting in a higher probability for late first rains to be more intense.