1956-2009年内蒙古苏尼特左旗荒漠草原的降水格局

弄清全球变化背景下不同地区降水格局的变化对科学理解气候变化及其影响具有重要意义。苏尼特左旗荒漠草原是温带干旱半干旱地区的典型荒漠草原,对气候变化,特别是降水变化非常敏感。利用1956-2009年的日降水资料探讨了苏尼特左旗荒漠草原降水格局的变化规律,以为揭示气候变化的影响机制提供依据。结果表明,该地区年均降水量为191.9 mm,年际变化剧烈,变异系数达26.63%;年均降水日数为63.8 d,变异系数16.9%。生长季降水占全年的85%,但各月变异系数均>50%;降水日数占全年的63%。年和生长季的各月降水以中等降水量、弱降水日数为主,中等强度以上降水事件较少。近50 a来,年和生长季的降水量、降水日数与各等级降水事件均呈下降趋势,年降水减少的原因在于中等降水事件的减少、生长季降水减少的原因在于弱降水事件的减少。年降水减少将影响草地的土壤水分与植物返青;而生长季降水减少将直接影响草地固碳。气候变化背景下年与生长季降水的减少将进一步加剧该地区干旱程度并影响植物的生长发育,从而直接威胁到草地畜牧业的发展。

Precipitation pattern of desert steppe in Inner Mongolia, Sunite Left Banner: 1956-2009

At present, precipitation pattern has taken significantly change under the effect of global change. To find out how precipitation pattern changes in different regions is very important to understand climate change and its consequences. The change of precipitation pattern includes variations of precipitation amounts, precipitation days, inter-precipitation periods and precipitation intensity. Desert steppe was the typical vegetation type in temperate arid and semi-arid regions, which was very sensitive to climate change, especially precipitation pattern changes. Precipitation was the main limiting factor in desert steppe ecosystem, whose variability determined the basic functions of this ecosystem. So it was in urgent need to find precipitation pattern variations in Chinese desert steppe under global change background. In this study, precipitation data from 1956 to 2009 in typical desert steppe of Sunite Left Banner in Inner Mongolia were collected and precipitation amounts, precipitation days, inter-precipitation periods and precipitation intensity were analyzed. Among them, Mann-Kendall method was used to analyze precipitation tendency and test significance, least square method was used to calculate the tendency values. The result showed that (1) from 1956 to 2009, the whole tendency of the annual precipitation amount and growing season precipitation amount were decreased, but the change tendency was different with the time. Among them, precipitation increased in 1970s but decreased in 1960s, 1980s and 1990s, then increased in 2000s. Annual mean precipitation amount was 191.9 mm, the range value was 100-250 mm, and the tendency value was -8.5 mm/10a. Amount of precipitation in the growing season accounted for 85% of the whole year's, which mainly occurred from June to August, and the variation coefficient of each month was above 50%. (2) Both mean annual precipitation days and short inter-precipitation period decreased but long inter-precipitation period increased from 1956 to 2009. Annual mean precipitation days were 63.8 days, the range value was 50-80 d, the tendency value was -2.5 d/10a and its variation coefficient was 16.9%. Number of precipitation days in the growing season accounted for 63% of the whole year's, and the variability of each month was above 28%, and tendency value was -3 d/10a. (3) Precipitation intensity was distinguished as six different types: light, relatively light, moderate, relatively heavy, heavy and extremely heavy. Precipitation events were dominated by moderate precipitation amounts and light rainfall days, and there were few events above moderate precipitation level, no matter in the whole year or each month of the growing season. Moderate precipitation accounted for 32% of annual precipitation amounts, and light precipitation accounted for 68% of the annual precipitation days. Precipitation decrease in the whole year mainly resulted from moderate precipitation events, while the decrease in precipitation during the growing season was primarily due to light precipitation events. In generally, from 1956 to 2009, mean annual precipitation amounts, precipitation days and the different precipitation types in the whole year and the growing season all decreased, particularly there was a consistent decline of annual precipitation days since 1990s. Decreasing annual precipitation would affect soil moisture and plant reviving, while decreasing precipitation in the growing season would directly affect carbon sequestration in the grasslands. Under the scenarios of climate change, reduced precipitation in the whole year and growing season would further exacerbate the degree of drought in this region and affect plant growth and development, and thereby to threat the development of grassland animal husbandry.