![]() On average over the central United States, more than 70% of annual precipitation falls during ~25% of rain days with totals above 12.7 mm. Several possible causes of observed changes in intense precipitation over the central United States are discussed and/or tested. With time, the internal precipitation structure (e.g., mean and maximum hourly precipitation rates within each preselected range of daily or multiday event totals) did not noticeably change. Tropical cyclones associated with extreme precipitation do not significantly contribute to the changes reported in this study. During the past 31 yr (compared to the 1948–78 period), significant increases occurred in the frequency of “very heavy” (the daily rain events above 76.2 mm) and extreme precipitation events (defined as daily and multiday rain events with totals above 154.9 mm or 6 in.), with up to 40% increases in the frequency of days and multiday extreme rain events. Moderately heavy precipitation events (within a 12.7–25.4 mm day −1 range) became less frequent compared to days and events with precipitation totals above 25.4 mm. Analyses show that over the central United States, a statistically significant redistribution in the spectra of intense precipitation days/events during the past decades has occurred. In examining intense precipitation over the central United States, the authors consider only days with precipitation when the daily total is above 12.7 mm and focus only on these days and multiday events constructed from such consecutive precipitation days. Note: the scales of the (top) and (bottom) differ by a factor of 2. ![]() All four linear trend estimates are statistically significant at the 0.01 level or higher. The trend estimates for the same periods are equal to 2.1% (10 yr) −1 and 4.6% (10 yr) −1 for days with totals above 76.2 mm and to 2.8% (10 yr) −1 and 6.9% (10 yr) −1 for days with totals above 101.6 mm, respectively. (bottom) Annual number of days with very heavy precipitation for the same region but defined as it is presently defined as days with daily rainfall totals above 76.2 mm and above 101.6 mm (red and black dots, respectively). These trend estimates are equal to 2.6% (10 yr) −1 and 7.4% (10 yr) −1, respectively, and are statistically significant at the 0.01 level or higher ( Groisman et al. (top) Annual number of days with very heavy precipitation (defined as an upper 0.3% of daily precipitation events) over regions of the central United States (upper Mississippi, Midwest, and South dark blue region in inset panel) and inferred linear trends for the 1893–20–2010 periods.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |