青藏高原草地降水利用效率时空动态及对气候变化的响应

本研究利用CASA(Carnegie-Ames-Stanford Approach)模型模拟了2000—2013年青藏高原草地净植被生产力(Net Primary Production，NPP)，结合实测数据、气象数据和土地覆被数据计算了草地降水利用效率（PUE），探究其时空分布特征，以及不同草地类型PUE及其对气候变化的响应。结果表明：青藏高原草地PUE在研究年限内呈现波动增加趋势，增加速率为每年0.0035 g·m^-2·mm^-1，14 a的平均值为0.38 g·m^-2·mm^-1。PUE的空间分布具有明显的异质性，呈现东部高、中西部低的基本格局。PUE分布在0.2～0.4 g·m^-2·mm^-1之间的比例最大，占青藏高原总面积的55.63%，呈减少趋势的区域主要分布在青藏高原的北部和西部，以及东部的边界地区，呈增加趋势的地区集中在研究区的中部和南部。研究年限内PUE的变异系数分布在0.07～0.85之间，变化稳定的区域所占面积最大，为总面积的43.43%，主要分布在唐古拉山脉和横断山脉附近。不同草地类型间PUE均值存在差异，具体表现为：草甸（1.06 g·m^-2·mm^-1）>坡面草地（0.80 g·m^-2·mm^-1）>平原草地（0.30 g·m^-2·mm^-1）>高山与亚高山草甸（0.29 g·m^-2·mm^-1）>荒漠草地（0.23 g·m^-2·mm^-1）>高山与亚高山草地（0.094 g·m^-2·mm^-1）。总体上，青藏高原草地PUE与降水成负相关关系，而与气温呈正相关，PUE的变化对降水响应更加敏感。

Spatial-temporal dynamics of precipitation use efficiency in grassland and its relationship with climate changes on Qinghai-Tibet Plateau

In this study, the Carnegie-Ames-Stanford Approach model was used to simulate the NPP of the Qinghai-Tibet Plateau from 2000 to 2013, PUE was calculated as the ratio of NPP to annual precipitation. Based on the measured data, meteorological data and land cover data, temporal and spatial distribution characteristics of PUE, PUE of different grassland type, and its response to climate change were also explored. The results showed: The PUE of the Qinghai-Tibet Plateau showed an increasing trend with fluctuation, with an annual increase rate of 0.0035 g·m^-2·mm^-1, and the average value of 14 a was 0.38 g·m^-2·mm^-1. The spatial distribution of PUE had obvious heterogeneity, and basically showed a decreasing pattern from the east to west. The grassland PUE mainly distributed between 0.2 and 0.4 g·m^-2·mm^-1, accounting for 55.63% of the total area of the Qinghai-Tibet Plateau. The areas where grassland PUE showed a decreasing trend mainly distributed in the northern and western regions of the Qinghai-Tibet Plateau, as well as the eastern border area. The regions showing increasing trend concentrated in the central and southern parts. The variation coefficient of PUE was between 0.07 and 0.85. The area with stable trend accounted for the largest area(43.43% of the total area), which mainly distributed in the Tanggula Mountains and Hengduan Mountains. The average PUE values of different grassland followed the order of: meadow(1.06 g·m^-2·mm^-1)>slope grassland(0.80 g·m^-2·mm^-1)>plain grassland(0.30 g·m^-2·mm^-1)>alpine and sub alpine meadow(0.29 g·m^-2·mm^-1)>dessert grassland(0.23 g·m^-2·mm^-1)>alpine and sub alpine grassland(0.094 g·m^-2·mm^-1). The grassland PUE was negatively correlated with precipitation but positively correlated with temperature. It was more responsive to precipitation.