Warm winters and high precipitation in north‐eastern Japan generate snow covers of more than three meters depth and densities of up to 0.55 g cm⁻³. Under these conditions, rain/snow ratio and snowmelt have increased significantly in the last decade under increasing warm winters. This study aims at understanding the effect of rain‐on‐snow and snowmelt on soil moisture under thick snow covers in mid‐winter, taking into account that snowmelt in spring is an important source of water for forests and agriculture. The study combines three components of the Hydrosphere (precipitation, snow cover and soil moisture) in order to trace water mobility in winter, since soil temperatures remained positive in winter at nearly 0.3°C. The results showed that soil moisture increased after snowmelt and especially after rain‐on‐snow events in mid‐winter 2018/2019. Rain‐on‐snow events were firstly buffered by fresh snow, increasing the snow water equivalent (SWE), followed by water soil infiltration once the water storage capacity of the snowpack was reached. The largest increase of soil moisture was 2.35 vol%. Early snowmelt increased soil moisture with rates between 0.02 and 0.035 vol% hr⁻¹ while, rain‐on‐snow events infiltrated snow and soil faster than snowmelt and resulted in rates of up to 1.06 vol% hr⁻¹. These results showed the strong connection of rain, snow and soil in winter and introduce possible hydrological scenarios in the forest ecosystems of the heavy snowfall regions of north‐eastern Japan. Effects of rain‐on‐snow events and snowmelt on soil moisture were estimated for the period 2012–2018. Rain/snow ratio showed that only 30% of the total precipitation in the winter season 2011/2012 was rain events while it was 50% for the winter 2018/2019. Increasing climate warming and weakening of the Siberian winter monsoons will probably increase rain/snow ratio and the number of rain‐on‐snow events in the near future.

中文翻译：

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日本东北部大雪条件下冬春季的土壤温度和水分动态

日本东北部温暖的冬季和高降水量产生的积雪深度超过三米，密度高达0.55 g cm ^-3。在这些条件下，近十年来，随着冬季的增加，雨雪比和融雪量显着增加。本研究旨在了解冬季中厚积雪下的雨雪和融雪对土壤水分的影响，同时考虑到春季融雪是森林和农业用水的重要来源。这项研究结合了水圈的三个组成部分（降水，积雪和土壤湿度），以追踪冬季的水迁移率，因为冬季土壤温度在接近0.3°C的情况下保持正值。结果表明，融雪后，尤其是2018/2019年冬季中雪降雨后，土壤水分增加。雪雨事件首先被新鲜的雪所缓冲，从而增加了雪水当量（SWE），一旦达到积雪的蓄水能力，随后水土入渗。土壤水分的最大增加量为2.35 vol％。早期融雪增加了土壤水分，速率为0.02至0.035 vol％hr^-1时，雪上降雨事件比融雪更快地渗透到雪和土壤中，导致hr ^-1高达1.06 vol％hr 。这些结果表明冬季雨，雪和土壤之间的联系紧密，并为日本东北大雪地区的森林生态系统引入了可能的水文情景。据估计，2012-2018年期间，雨雪事件和融雪对土壤水分的影响。雨雪比表明，2011/2012年冬季只有30％的降雨是降雨事件，而2018/2019年冬季则为50％。气候变暖的加剧和西伯利亚冬季风的减弱可能会在不久的将来增加雨雪比和雪上降雨事件的数量。