In cold conditions, early winter precipitation occurs as snowfall and contributes to the accumulating seasonal snowpack. In a warming climate, precipitation may occur as rainfall in mountainous areas. Detecting changes during seasonal transitions is difficult because these may encompass changes in timing, magnitude and phase, which may not be consistent between years. In this study, a sampling window from September to December is used to assess trends in magnitude, frequency and duration (of rainfall, snowfall and runoff events) in 127 climate stations and 128 watersheds with more than 30 years of record across the Rocky Mountains of North America. Rainfall events have increasing frequencies and durations, and magnitude trends are predominantly increasing at mid-latitude and mid-elevation. Snowfall events have the largest numbers of significant trends, with both increasing and decreasing trends in each of magnitude, frequency and duration. Snowfall events have decreasing frequencies and durations in the northern low-elevation sites and increasing frequencies and durations at the southern high-elevation sites. Trends in runoff events are less common than for rainfall and snowfall but are greater than expected by chance, and show similar frequency and duration patterns to snowfall trends. Snowfall and runoff events are decreasing in frequency and duration north of Wyoming and increasing to the south. Snowfall magnitude is generally decreasing to the north and increasing to the south, with runoff magnitude trends showing the reverse.

在寒冷的条件下，冬季早期的降水会随着降雪而发生，并导致季节性积雪的积累。在气候变暖的情况下，山区可能会出现降雨。很难检测季节转换期间的变化，因为这些变化可能包含时间，幅度和相位的变化，这可能在几年之间不一致。在这项研究中，使用9月至12月的采样窗口来评估127个气候站和128个流域（在落基山脉有30多年的记录）的幅度，频率和持续时间（降雨，降雪和径流事件）的趋势。北美。降雨事件的频率和持续时间不断增加，在中纬度和中海拔高度，幅度趋势主要在增加。降雪事件的重要趋势数量最多，幅度，频率和持续时间各有上升趋势和下降趋势。降雪事件在北部低海拔站点的频率和持续时间减少，而在南部高海拔站点的频率和持续时间增加。与降雨和降雪相比，径流事件的趋势不那么普遍，但偶然性所期望的趋势却更大，并且与降雪趋势的频率和持续时间趋势相似。降雪和径流事件的频率和持续时间在怀俄明州以北逐渐减少，而在南部一直在增加。降雪量通常向北减少，向南增加，径流趋势呈相反趋势。降雪事件在北部低海拔站点的频率和持续时间减少，而在南部高海拔站点的频率和持续时间增加。与降雨和降雪相比，径流事件的趋势不那么普遍，但偶然性所期望的趋势却更大，并且与降雪趋势的频率和持续时间趋势相似。降雪和径流事件的频率和持续时间在怀俄明州以北逐渐减少，而在南部一直在增加。降雪量通常向北减少，向南增加，径流趋势呈相反趋势。降雪事件在北部低海拔站点的频率和持续时间减少，而在南部高海拔站点的频率和持续时间增加。与降雨和降雪相比，径流事件的趋势不那么普遍，但偶然性所期望的趋势却更大，并且与降雪趋势的频率和持续时间趋势相似。降雪和径流事件的频率和持续时间在怀俄明州以北逐渐减少，而在南部一直在增加。降雪量通常向北减少，向南增加，径流趋势呈相反趋势。与降雨和降雪相比，径流事件的趋势不那么普遍，但偶然性所期望的趋势却更大，并且与降雪趋势显示相似的频率和持续时间模式。降雪和径流事件的频率和持续时间在怀俄明州以北逐渐减少，而在南部一直在增加。降雪量通常向北减少，向南增加，径流趋势呈相反趋势。与降雨和降雪相比，径流事件的趋势不那么普遍，但偶然性所期望的趋势却更大，并且与降雪趋势显示相似的频率和持续时间模式。降雪和径流事件的频率和持续时间在怀俄明州以北逐渐减少，而在南部一直在增加。降雪量通常向北减少，向南增加，径流趋势呈相反趋势。