内蒙古典型草原返青期变化及其气候驱动机理研究

Studying on the spatio-temporal change in the green-up dates for typical steppe in Inner Mongolia and its climate-driven mechanism can monitor change on primary productivity in the steppe accurately and enhance our understanding about the response of vegetation to global climate change. Two types of typical steppe (i.e. Stipa grandis steppe, Leymus chinensis steppe) will be selected as the research subjects in this proposed project. We first develop a green-up date retrieval method and its authentication method from remote sensing data based on the ground investigation, and achieve the green-up dates from ground fixed-point observation scale up to a wide range of spatial scale observation based on remote sensing. Then, combining phenology model simulation results, this proposed project integrates three monitoring means (i.e. ground investigation, remote sensing monitoring and model simulation) to carry out a comprehensive analysis about the spatio-temporal change in green-up date of steppe in Inner Mongolia during recent 34 years after supplement and validation with each other. Finally, using phenology model as the bridge, we study the change in the green-up dates for typical steppe in Inner Mongolia and its climate-driven mechanism quantitatively, and achieve deeply combination for ground investigation and remote sensing monitoring from the data level to the level of phenology mechanism. This proposed project can deepen understanding for mechanism of vegetation phenology, and provide a new method for monitoring vegetation phenology at a wide (or global) range accurately, assessing the global climate change impacts on ecosystems quantitatively, and predicting the change trend for vegetation phenology in the future.

研究内蒙古典型草原植被返青期时空变化及其气候驱动机理，对于准确监测草原生产力变化、深化认识植被对全球气候变化的响应规律具有重要意义。本项目以内蒙古两种典型的草原类型（针茅草原和羊草草原）为研究对象，首先立足地面物候观测结果，发展遥感返青期识别及其验证方法，实现地面返青期定点观测向大范围遥感监测的空间尺度拓展；然后结合物候模型模拟结果，对地面、遥感、模型模拟三种监测结果进行相互验证及补充，综合评估近34年（1982-2015）来内蒙古草原植被返青期的时空变化情况；最后以物候模型为桥梁，定量研究返青期变化的气候驱动机理，实现地面观测与遥感监测从数据层面到物候机理层面的有机结合。本项目能够加深对植被物候变化机理的认识，并为大范围（或全球）植被物候的准确监测、全球气候变化对生态系统影响的定量评估、植被未来物候变化趋势预测等研究工作提供一种新方法。

评估内蒙古典型草原返青期变化规律并研究其气候驱动机理，有助于探索植被对全球气候变化的响应规律。本项目综合运用遥感监测数据和地面物候观测数据，研究并验证了羊草草原返青期识别方法，提出了适用于内蒙古草原温带干旱-半干旱气候条件的温度-降水联合驱动物候机理模型，借此定量分析了温度、降水变化对返青期的影响，评估了近55年（1962～2016）内蒙古典型草原返青期时空变化规律及成因，获得了以下重要研究结果：（1）基于SG滤波拟合及滑动平均法识别返青期，遥感识别返青期变化趋势与地面观测结果更为一致。（2）在覆盖羊草草原的各气象站点附近，基于遥感监测数据的温度-降水联合驱动物候模型获取的羊草草原的近55年返青期均呈提前趋势。（3）羊草草原返青期对四季温度和降水变化的敏感性为：秋冬变暖会导致返青期延后，春季变暖会导致返青期提前；秋、冬、春季降水量增加会导致返青期提前，其中，返青期对秋季、冬季降水量的敏感度更高，对3月、4月降水量的敏感度次之，对5月降水量的敏感度略低。近55年来内蒙古羊草草原返青期变化与春季变暖、秋季至春季降水量增加密切相关。（4）将地面物候观测、遥感监测、模型模拟三种手段结合，分析了近55年内蒙古羊草草原返青期提前的气候驱动机理：近55年驱动积温作用在增强，冷激积温作用在减弱，这主要是由于近几十年来内蒙古地区秋季至冬季的气温均在升高，一方面使羊草草原不能经历足够的抗寒锻炼，另一方面，由于春季温度升高更为明显，导致其驱动作用的增强幅度大于冷激作用受抑制的幅度；加之秋季至春季的累计降水量有所增加，适宜的温度、水分条件又进一步降低了对驱动作用的需求，在温度和降水的联合调控下，使得羊草草原的返青期呈现提前趋势。通过该项目，有效拓展了物候模型的应用范围，降低了基于有限样本和有限时段的地面及遥感物候观测数据可能带来的对返青期变化趋势认知的不确定性。