2000-2014年宁夏草地蒸散时空特征及演变规律

蒸散是水文-生态过程耦合的纽带,对草地生态系统的稳定性十分重要,研究生态环境脆弱地区草地生态系统蒸散变化特征对于区域农牧业发展、生态恢复与重建和构建生态屏障意义明显。基于2000-2014年MOD16地表蒸散数据,利用回归分析、相关分析和重新标度极差分析等方法,研究了宁夏草地近15年的蒸散时空分布格局与演变规律,并讨论了可能影响因素。结果表明,2000-2014年,宁夏草地蒸散量介于177.51~274.43 mm,平均值为228.03 mm;受降水的年际波动影响,全区草地蒸散量在近15年呈不显著的上升趋势(P>0.05),不同类型草地的年蒸散量和月蒸散变化动态差异明显;从空间上来看,宁夏草地的多年平均蒸散量存在较强的空间异质性,呈现南高北低的分布格局,北部最低为135.84 mm,南部最高可达732.12 mm,但波动性不强;近15年,宁夏北部草地的蒸散以下降为主,降幅自北向南递减,中部和南部以上升为主,增幅自北向南递增,但大部分区域的蒸散变化幅度较小,总体变化不显著;未来,全区草地蒸散的正向特征显著,趋势发生反转的草地比例较小;降水量是决定全区草地蒸散空间分布格局和年际波动的主要因素,人类生产活动主导的土地利用类型变化对局部蒸散的影响不容忽视。

Spatio-temporal characteristics and evolution of evapotranspiration of natural grassland in Ningxia during 2000-2014

Evapotranspiration (ET),a link between hydrological and ecological processes,is very important to the stability of terrestrial ecosystems.In arid and semi-arid regions,where more than 90 ％ of the effective precipitation is consumed by ET,variations in ET processes may weaken the stability of a grassland ecosystem plagued by water stress.Ningxia is located in the north China farming-grazing transitional zone;long term excessive conversion to farmland and overgrazing have greatly decreased the ecological function of the grassland ecosystem and generated serious changes in ET processes.Background information on grassland ET in the region is unknown,due to inadequate research on the characteristics of ET in undisturbed grassland in Ningxia.Research on the ET characteristics of grassland ecosystems within fragile ecological environments are important for regional agriculture and animal husbandry development,ecological restoration and reconstruction,and the construction of eco-barriers.This study,based on MOD16 ET data,corresponding climate data and grassland type,analyzed the spatial-temporal changes in ET in Ningxia from 2000 to 2014 and predict future trends.Regression analysis,correlation analysis and rescaled range analysis were employed.The results indicated that during a recent 15-year period (2000-2014),the ET of grassland increased (with fluctuations) and average ET was 228.03 mm per year.The upward trend was not significant (P＞0.05) because of regional differences in precipitation and heat,and the annual and monthly ET of various grassland types presented obvious heterogeneity.The annual average ET also had a strong spatial heterogeneity (135.84-732.12 mm),higher ET in the south and lower in the north,but the fluctuation was small.More specifically,grassland ET mainly presented a decreasing pattern from north to south in northern Ningxia,and increasing from north to south in central and southern Ningxia.However,the variation in ET is small and the change is not significant in most of the study area.In the future,the increasing trend of ET in the grasslands will probably become significant and only small parts of the grassland system will experience reduced ET.Precipitation was the main factor determining the distribution pattern and inter-annual fluctuation of ET in grassland in Ningxia.Nevertheless,the influence of land use change caused by human activities in ET cannot be ignored.