关键词: 水分利用效率, 植被类型, 干旱, “三北”工程区

Abstract:

Objective: This study aims to investigate the spatiotemporal variations of vegetation water use efficiency (WUE) and its responses to environmental factors and drought events, thereby providing scientific support for the sustainable management of regional ecosystems and drought adaptation strategies. Method: Based on vegetation gross primary productivity (GPP) and evapotranspiration (ET) data from 2001 to 2022, and in combination with meteorological observations, water-use efficiency (WUE=GPP/ET) was computed for each pixel at a 500 m resolution. The spatiotemporal patterns of WUE and standardized precipitation evapotranspiration index (SPEI-12, the cumulative severity of drought for each year from January to December) in the study area were analyzed. Partial correlation analysis was employed to explore the relationships between WUE and key environmental factors (temperature and precipitation), as well as drought intensity, and to further examine the response of WUE to drought intensity across different vegetation types. Result: 1) The mean annual WUE in the Three-North regions was (1.12 ± 0.35) g·kg^?1 during 2001—2022. Spatially, WUE showed significant increase (P<0.05) in most northwestern desert region (excluding southern Xinjiang), thehilly and gully region of the Loess Plateau, and the centralagricultural region of northeast and north China plain, while WUE in southern Xinjiang, aeolan sand area, and the northern agricultural region of northeast and north China plain decreased significantly (P<0.05). 2) The response of WUE to precipitation and temperature exhibited marked spatial heterogeneity. WUE in most area of the northwestern desert region, the hilly and gully region of the Loess Plateau, the aeolan sandy region, and the central agricultural region of the northeast and north China plain was primarily influenced by variations in precipitation. In contrast, WUE in the Junggar basin and Tarim basin peripheries, the central hilly and gully region of the Loess Plateau, the Hunshandake and Hulunbuir sandy lands, as well as the southern part of the northeast–north China plain agricultural region was predominantly affected by temperature changes. 3) In humid regions, vegetation WUE increased with the intensification of drought, whereas in arid regions, it showed the opposite trend. Additionally, WUE responses to drought varied across vegetation types, the WUE of forests and grasslands significantly increased under mild and moderate drought conditions, but significantly decreased under severe and extreme drought conditions, with grasslands showing lower sensitivity. The WUE of shrubs significantly increased under mild drought conditions, but significantly decreased under moderate and severe drought conditions. Conclusion: The vegetation WUE in the Three-North Shelterbelt Forest Program Region exhibits a spatial distribution pattern that decreases progressively from east to west. In the humid regions, WUE increases with the intensification of drought, while there are significant differences in the response strategies of WUE to environmental changes and droughts across different vegetation types, with grasslands being particularly sensitive to drought. Therefore, it is essential to develop tailored management strategies based on the natural conditions and vegetation characteristics of each region.

Key words: water use efficiency, vegetation type, drought, Three-North Shelterbelt Forest Program Region