科尔沁沙地降雨特征分析——以奈曼旗为例

了解降水的当前特征及未来的变化趋势对理解气候变化对区域生态系统的影响具有重要的意义。科尔沁沙地是中国北方农牧交错带的典型区域,年降雨量300~500 mm,对气候变化(特别是降水的变化)非常敏感。对科尔沁沙地沙漠化较为严重的奈曼旗1971-2013年的降水资料进行了分析研究。结果表明:(1)该地区多年平均降水量为338.8 mm,5-9月降雨量占全年降水量的(85.32±7.71)%,5-9月降雨量,年降水量1971-2000年经历了先增加后减少的趋势,2001-2013年有缓慢增加的趋势;同时降水量的年际变异性近10年也呈增加的趋势。(2)5-9月降雨量呈先增大后减小的趋势,在7月最大,为104.2 mm,5月和9月最小(分别为32.7 mm和32.8 mm),月降雨量的年际变率均大于49%;生长季内降雨主要以<10 mm的事件为主,占总降雨事件的64.41%,却仅占总降雨量的16.95%;≥30 mm的降雨事件占总降雨事件的10.96%,占到总降雨量的45.93%,且对总降雨量具有决定性的影响。(3)≥5 mm降雨的平均间隔为9.4 d,以1~10 d为主,占到69.5%,10~20 d(19.5%)的次之;≥30 d的发生频率最小,为3.81%,降雨间隔的年际变异性均呈增加的趋势。(4)生长季降雨日数呈减少的趋势,降雨事件降雨量的变异性与生长季降雨量的变化具有相似性,从2001年开始呈增加的趋势。该地区的降雨量年际变异性强,降雨日数的减少和降雨事件降雨量变异性的增加将提高极端干旱事件发生的频率,可能对该地区的生态系统产生严重影响,加剧该地区的沙漠化发展方向。因此,加强气候变化对生态系统影响的研究,可为合理利用土地资源及调整土地管理方式提供理论依据。

Characteristics of Precipitation in Growing Season in the Horqin Sandy Land: a case study in Naiman,Inner Mongolia,China

Global change had a significant influence to precipitation regimes. To understand the current rainfall pattern and find out how it will change in different regions is important to understand its consequences and take reasonable measures of land management. The Horqin Sandy Land is one of the typical regions in transition zone between cropping area and nomadic area of northern China, and in which the plant communities were very sensitive to climate change, especially rainfall pattern change. The rainfall characteristics includes rainfall amount, rain days, rain event size and inter-events intervals, which determined the basic biotical processes by affecting the soil moisture directly. In this region, the situation of desertification was still arduous, so it was urgent to know the rainfall pattern variations in the context of global climate change. In this study, precipitation date from 1971 to 2013 in Naiman Banner including rainfall amount, rain days, rain-events size and inter-events intervals was analyzed. The result showed that (1) from 1971 to 2000, the annual precipitation, rainfall amount and variability of rainfall events size during growing season (from May to September) all increased in 1970s-1980s then decreased in 1990s, and tended to increase in 2000s. Annual mean rainfall was 291.9 mm, accounting for 85.32% of annual precipitation (338.8 mm). (2) During the growing season, the rainfall in July was maximum (104.2 mm), May (32.7 mm) and September (32.8 mm) were minimum, and the variation coefficient of rainfall per month were all above 0.49. The rainfall pattern was characterized by small events (<10 mm), which accounting for 64.41% of the total events and only 16.95% of the total rainfall, while the large events (≥30 mm) accounted 12.47% of total events and 48.17% of the total rainfall which determined the annual precipitation. The intra-annual variation of events size tended to increase. (3) The mean interval between 2 effective events (≥5 mm) was 9.4 d, and the short intervals (1-10d) was dominated. The mean annual rain-days (43.1 d) tended to decrease by 2.8 d/10a, while the intra-annual variation of intervals tended to increase. Consequently, under the scenarios of climate change, the increasing variability of rainfall pattern may affect the carbon cycle in the grassland and exacerbate the degree of drought in this region which may influence the stability of local grassland ecosystem, and threat the development of animal husbandry.