Precipitation use efficiency (PUE) is an effective index to evaluate the relationship between grassland productivity and precipitation in arid and semi-arid regions. To explore the driving mechanism of climate change and human activities on grassland PUE, we used the improved CASA model to estimate net primary productivity (NPP) of grassland from 2001 to 2020 in Otog Banner, Inner Mongolia. The PUE was obtained combining with the spatial interpolation data of precipitation. The spatiotemporal evolution of PUE and its responses to the six climate factors were analyzed using simple and piecewise linear regression. A quantitative analysis method based on partial derivatives was used to quantitatively evaluate the relative contributions of climate change and human activities to PUE dynamics. The results showed that the annual average value of PUE was 0.748 g C·m-2·mm-1 in Otog Banner, and that the inter-annual fluctuation had a significant downward trend at a rate of 0.014 g C·m-2·mm-1·a-1. Across the study area, PUE increased from west part to east part, and exhibited significant single-peak piecewise linear patterns along the growth gradients of temperature, precipitation, relative humidity, sunshine hours, and ET0. There was a sustained and significant increase pattern of fast first and then slow along the wind speed gradient. 94.3% of the grassland in the study area showed a decrease trend in PUE, and 43.6% area showed severely decreased. This prominent decrease in PUE was co-driven by climate change and human activities, whose contributions were -1.162×10-2 and -0.240×10-2 g C·m-2·mm-1·a-1, respectively. Climate change was the primary driving force and precipitation was the key climate driving factor for the decrease in PUE.
降水利用效率(PUE)是评价干旱半干旱地区草地生产力与降水关系的有效指标。为进一步探究气候变化和人类活动对草地PUE的驱动机理,本研究采用改进的CASA模型估算了2001—2020年鄂托克旗草地净初级生产力(NPP),结合同期降水量的空间插值数据获取了研究区草地PUE,利用简单线性回归和分段线性回归分析了PUE的时空演变特征及其空间格局对6类气候因子的响应,并引入基于偏导数的量化分析方法定量评估了气候变化和人类活动对PUE动态的相对贡献。结果表明: 鄂托克旗草地PUE多年均值为0.748 g C·m-2·mm-1,年际波动呈显著下降趋势,下降速率为0.014 g C·m-2·mm-1·a-1;PUE在空间上西低东高,沿气温、降水、相对湿度、日照时数和ET0的增长梯度呈显著的单峰分段线性模式,而沿风速梯度表现为先快后慢的持续显著增长模式;研究区94.3%的草地表现为PUE衰减态势,且有43.6%为严重衰减,这一突出问题是气候变化和人类活动共同作用导致的,二者的贡献分别为-1.162×10-2和-0.240×10-2 g C·m-2·mm-1·a-1,而气候变化是首要驱动力,其中降水是关键气候驱动因子。.
Keywords: climate change; human activity; precipitation use efficiency; spatiotemporal evolution.