Spatiotemporal patterns and variations of winter extreme precipitation over terrestrial northern hemisphere in the past century (1901–2017)

In this study, the spatiotemporal distributions and variation characteristics of winter extreme precipitation in the Northern Hemisphere over the past century (1901–2017) were analyzed using trend analysis and spatial analysis. These analyses utilized the monthly average dataset of surface climatic factors (CRU TS4.03), and years with extreme precipitation was defined based on the standard deviation method. The following results were obtained. (1) In the past century, the frequency of years with more winter extreme precipitation (denoted as more-extreme years) in the Northern Hemisphere was higher than that of years with less winter extreme precipitation (denoted as less-extreme years), with return periods of 10 years and 14 years, respectively. The frequency of more-extreme years increased significantly (P < 0.05), and the less-extreme years were minimal changes (P > 0.05) (2) The frequencies of more-extreme years and less-extreme years were higher in middle and high latitudes than in low latitudes. Significant increases in the frequencies of more-extreme years were observed in middle and high latitudes, while an significant increase in the frequency of less-extreme years was observed in low latitudes. The frequency of more-extreme years in high latitudes increased the most rapidly. (3) In the past century, the frequencies of more-extreme years and less-extreme years over terrestrial Northern Hemisphere ranged from 5 to 15%. The frequency of more-extreme years tended to increase over approximately 2/3 of the Northern Hemisphere, and increased significantly over approximately 1/5 of the Northern Hemisphere. In contrast, the frequency of less-extreme years tended to increase over 1/2 of the Northern Hemisphere, and increased significantly over 1/10 of the Northern Hemisphere. (4) Spatially, at high latitudes, the proportions of grid points with more-extreme years and less-extreme years were the largest, and the increase in the variation of winter extreme precipitation was the greatest. In low latitude areas, the number of grid points with significant decreases of more-extreme years was smaller than the number with significant increases of less-extreme years, indicating that low latitudes were mainly dominated by an increase in the frequency of less-extreme years.