松嫩平原百年草甸农田化的干旱效应及其物理机制

In the domestic and international history, there is a significant drought effects caused by large scale and high intensity farmland expansion, and the deterioration of the ecological environment caused by this kind of drought effects have become an indisputable fact. The Songnen Plain, located in Northeast of China has experienced a significant surface change process from meadow to farmland, which has been driven by the migration northward expansion in hundred years, and cause obvious aridity and degradation of the ecological environment. However, there is little research about the conversion effect from meadow to farmland. This study takes the meadow farmland process and drought effect of the Songneng Plain in hundred years as study object, the internal conditions of the natural geographical unit as the basis, according to the meteorological observations data of farmland expansion for centuries, try to reveal the cultivation pattern and driving mechanism under centennial heavy human activity on the the Songnen Plain,and try to examine the drought effects and mechanisms caused by farmland expansion on the Semi arid and semi humid transition zone,and try to certain the agricultural development's "contributing rate" on the regional drought in the LUCC process about the conversion from grassland to cultivated land using statistic analysis, numerical simulation and GIS spatial analysis. This study will enrich and develop the theory and practice of regional environmental change study. It has a significant theoretical meaning and practical value for regional sustainable development and promotes the harmonious development of the relationship between human being and nature.

在国内外历史上，大规模、高强度农田扩张无一例外地引起干旱效应而造成生态环境恶化。位于东北地区的松嫩平原百年来在移民北扩的驱动下，高强度垦殖使地表发生了由草甸变成耕地的巨大变化过程，区域明显干旱化，并引起生态环境退化。但目前有关草甸转化为农田的气候效应研究成果较少。本研究以松嫩平原百年草甸农田化过程及干旱效应为研究对象，以内部条件一致的自然地理单元为基础，以百年来农田扩张及气象观测资料为依据，结合区域气候模式模拟及野外实地观测，采用统计分析、数值模拟、GIS空间分析等研究方法，揭示近百年来人类活动对松嫩平原高强度垦殖模式及驱动机制，探讨半干旱半湿润过渡区农田扩张对区域干旱化趋势的影响及物理机制，厘定以草甸农田化为特征的LUCC过程对区域干旱化的贡献率。丰富和发展区域环境变化的理论和实践，对实现区域可持续发展，促进人与自然关系和谐发展，具有重要的理论意义和实践价值。

松嫩平原1910s—2010s耕地面积增加了2.67倍，自然地表的38.07%变为了耕地，耕地垦殖率由22.78%增加至60.85%，耕地扩张表现出由松嫩平原东南部逐渐向中部、西部、西北部的空间扩张态势。松嫩平原过去百年以草地面积减少并转化为耕地为最主要的土地利用变化类型，草地面积减少了85840 km2，减小幅度为83.38%，集中分布在松嫩平原中部和西部；松嫩平原过去百年平均气温、最高气温、最低气温极显著升高，气温日较差和霜日数极显著下降，水汽压显著增加，降水量、蒸发量及云量不显著增加，降水日数不显著减少，全区域干燥度、PDSI和SPI均为不显著变湿趋势；松嫩平原20世纪末期与初期相比，气候呈现暖干化。其平均气温、最高气温、最低气温、气温日较差、蒸发量、水汽压均显著增加，云量、霜日数显著减少，降水量、降水日数、干燥度无显著差异，PDSI 、SPI均有显著变干趋势；松嫩平原百年LUCC加大了气温的空间变异，但并没有改变气温随纬度的带状分布特征，松嫩平原百年以草地转耕地为主要特征的农田扩张，在作物生长季表现出致干制冷的气候效应，其空间变化特征与耕地重心转移方向一致；耕地与草地相比，使最高气温升高，最低气温降低，土壤湿度、相对湿度、风速等均低于草地；草地转为耕地，使夏季地表反射率减小，显热通量增加，潜热通量减少是致干致冷的物理机制；松嫩平原LUCC变化对年平均气温升高的贡献率为12%，对春季、秋季气温的贡献率高于夏季和冬季，而草地转耕地集中区对于夏季和冬季气温变化的贡献率增大；草地转为耕地使干燥度和PDSI有变干效应，使对区域干燥度变干的贡献率为23.75%，对PDSI变干的贡献率为21%；松嫩平原西部、东北部尚有耕地潜在资源面积为33597.73 km2，以草地、沼泽地和盐碱地为主；人类活动增强了松嫩平原地理单元的异质性，以人类活动为特质的地理单元显著增加。