近50年黄土高原地区降水时空变化特征

根据黄土高原地区214个地面气象站最近50年(1961-2010年)的逐日降水量数据, 采用非参数Mann-Kendall和Mann-Whitney法,从黄土高原地区、典型黄土高原和综合治理分区3个层面,对本地区年降水量(PTOT)、侵蚀性降水量(R12mm)、汛期降水量(RJJAS)和暴雨量(R50mm)的时空变化特点进行了研究。结果表明:(1)在黄土高原地区,PTOT、R12mm和RJJAS变化的空间格局基本一致,从东南向西北,其减少幅度逐渐变小,至西北部和最西部,其反而略有增加。但是R50mm变化的空间趋势不大明显。相比之下,典型黄土高原PTOT、R12mm和RJJAS变化的空间趋势更为突出。(2)在黄土高原地区,约83%的站点PTOT呈减少趋势,69%的站点R12mm和RJJAS呈减少趋势;其中20%的站点PTOT减少显著,10%的站点R12mm和RJJAS减少显著。而约68%的站点R50mm变化率为零。相比之下,在典型黄土高原,呈减少或显著减少趋势的站点比例较高,约92%的站点PTOT呈减少趋势,80%的站点R12mm和RJJAS呈减少趋势;其中24%的站点PTOT减少显著,12%的站点R12mm和RJJAS减少显著。R50mm变化率为零的站点比例则较底,约占62%。(3)近50a黄土高原地区的PTOT和R12mm总体上分别呈显著和接近显著减少趋势,递减率分别为9.9mm/10a和5.9mm/10a;但是其RJJAS和R50mm的减少不显著。近50a典型黄土高原的PTOT和R12mm均呈显著减少趋势,递减率分别为13.4 mm/10a和8.1mm/10a。其RJJAS减少趋势接近显著,递减率为7.6mm/10a。但是其R50mm减少不显著。(4)就5个综合治理区而言,第Ⅰ区和第Ⅱ区的PTOT总体呈显著减少趋势,这两个区的R12mm分别呈接近显著和显著减少趋势,而第Ⅲ至Ⅴ区的PTOT和R12mm总体呈不显著增加趋势。仅第Ⅱ区的RJJAS呈显著减少趋势。R50mm在第Ⅰ区、第Ⅱ区和第Ⅳ区减少不显著,在第Ⅲ区和第Ⅴ区变化率为零。(5)近50aPTOT减少的突变时间在黄土高原地区、典型黄土高原和综合治理第Ⅱ区始于1986年, 在第Ⅰ区始于1991年。PTOT在其余3个区没有出现突变现象。这些结果表明,在典型黄土高原,尤其是其水土保持重点区(即第Ⅱ区),近50a的年降水量、侵蚀性降水量和汛期降水量明显减少,但暴雨量却未显著减少。这意味着如果此种趋势继续下去,尽管因水蚀导致的土壤侵蚀量总体上会有所减少,但是缺水情形会更为严峻,因暴雨导致的剧烈水土流失仍不会有明显缓解。

Precipitation trends during 1961-2010 in the Loess Plateau region of China

Precipitation change could exert considerable impacts on the soil and water conservation and ecological construction in the Loess Plateau region. In this study a dataset of daily precipitation series (1961-2010) from 214 surface meteorological stations was used to investigate the spatiotemporal change trends in annual precipitation (PTOT), annual erosive rainfall (R12mm), annual flood season rainfall (RJJAS) and annual torrential rainfall (R50mm) over the Loess Plateau region (LPR) during the period 1961-2010. The examination was made at three hierarchical levels: the entire LPR, the Loess Plateau (LP) and the five divisions of integrated management of the LPR, and the Mann-Kendall and Mann-Whitney methods were used to test the monotonic and step trends, respectively. Results showed that (1) a similar spatial pattern of distribution of change trends at all the stations was found for PTOT, R12mm and RJJAS over the LPR, with a decreasing magnitude of negative change from the southeast to the northwest, besides a slightly positive change in the far northwest and far west areas. However, no clear spatial pattern was observed for R50mm over the region. The spatial patterns for PTOT, R12mm and RJJAS were more profound on the LP than on the LPR. (2) On the LPR, approximately 83% of stations showed a negative change in PTOT, and 69% of stations showed a negative change in R12mm and RJJAS, while 20% of stations showed a significant decrease in PTOT, and 10% of stations showed a significant decrease in R12mm and RJJAS. However, approximately 68% of stations showed a zero slope in R50mm. The proportion of stations showing a negative change or a significant negative change on the LP was higher than on the LPR, about 92% of stations showed a negative change in PTOT, and 80% of stations showed a negative change in R12mm and RJJAS, while 24% of stations showed a significant decrease in PTOT, and 12% of stations showed a significant decrease in R12mm and RJJAS. Approximately 62% of stations showed a zero slope in R50mm on the LP. (3) As a whole, a significant negative trend (P<0.05) in PTOT and a nearly significant negative trend (P<0.10) in R12mm were found on the LPR, with a linear trend of -9.9mm/10a and -5.9mm/10a, respectively; while the decrease was not significant for RJJAS and R50mm over the LPR. A significant negative trend for PTOT and R12mm, and a nearly significant negative trend for RJJAS were found on the LP, with a linear trend of -13.4mm/10a, -8.1mm/10a and -7.6mm/ 10a, respectively; while the decrease was not significant for R50mm over the LP. (4) The first and the second divisions of the LPR showed a significant negative trend in PTOT, and they showed a nearly significant negative trend and a significant negative trend for R12mm, respectively, while the rest three divisions showed a non-significant positive trend for PTOT and R12mm. A significant negative trend in RJJAS was only found in the second division among the five divisions. The first, second and fourth divisions showed a non-significant decrease in R50mm, while the third and fifth ones showed a zero slope in R50mm. (5) One abrupt change was detected in PTOT for the LPR, LP, and the first and second divisions, but not for the rest three divisions, with a significant decrease occurred since 1986 for the LPR, LP, and the second division, and since 1991 for the first division. Overall, the PTOT, R12mm and RJJAS decreased substantially but the R50mm did not change significantly over the LP, especially over the key area of soil and water conservation of the LPR (i.e. the second division) over the past five decades. These results indicated that if the trends are hold in future, although the soil erosion resulted from R12mm may decrease as a whole, the shortage of water resource will become severer, and the situation of the extremely intense soil and water losses caused by R50mm will not have considerable change.