Increasing water demand due to population growth, economic development, and changes in rainfall patterns due to climate change are likely to alter the duration and magnitude of droughts. Understanding the relationship between low-flow conditions and controlling factors relative to the magnitude of a drought is important for establishing sustainable water resource management based on changes in future drought risk. This study demonstrates the relationship between low-flow and controlling factors under different severities of drought. I calculated the drought runoff coefficient for six types of occurrence probability, using past observation data of annual total discharge and precipitation in the Japanese archipelago, where multiple climate zones exist. Furthermore, I investigated the pattern of change in the drought runoff coefficient in accordance with the probability of occurrence of drought, and relationships among the coefficient and geological, land use, and topographical factors. The drought runoff coefficient for multiple drought magnitudes exhibited three behaviors, corresponding to the pattern of precipitation. Results from a generalized linear model (GLM) revealed that the controlling factors differed depending on the magnitude of the drought. During high-frequency droughts, the drought runoff coefficient was influenced by geological and vegetation factors, whereas land use and topographical factors influenced the drought runoff coefficient during low-frequency droughts. These differences were caused by differences in runoff, which dominated stream discharge, depending on the magnitude of the drought. Therefore, for effective water resource management, estimation of the volume of drought runoff needs to consider the pattern of precipitation, geology, land use, and topography.

中文翻译：

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干旱径流系数的特征及控制因素

由于人口增长，经济发展以及气候变化引起的降雨模式变化而导致的需水量增加可能会改变干旱的持续时间和程度。理解相对于干旱程度的低流量条件和控制因素之间的关系，对于根据未来干旱风险的变化建立可持续的水资源管理非常重要。这项研究证明了在不同严重干旱条件下低流量与控制因素之间的关系。我使用存在多个气候区的日本群岛的年度总排放量和降水量的过去观测数据，计算了六种发生概率的干旱径流系数。此外，我根据干旱发生的可能性以及干旱系数与地质，土地利用和地形因素之间的关系，研究了干旱径流系数的变化模式。不同降水量的干旱径流系数表现出三种行为，与降水模式相对应。广义线性模型（GLM）的结果表明，控制因素根据干旱的程度而有所不同。在高频干旱期间，干旱径流系数受地质和植被因素的影响，而土地利用和地形因素对低频干旱期间的径流系数产生影响。这些差异是由径流差异引起的，而这些差异主要是水流的排放，取决于干旱的严重程度。因此，为了进行有效的水资源管理，对干旱径流量的估算需要考虑降水的方式，地质，土地利用和地形。