Assessment of the spatiotemporal characteristics of vegetation water use efficiency in response to drought in Inner Mongolia, China.

Abstract

Ecosystem water use efficiency (eWUE) can be used to obtain a better comprehension of the ecosystem water-carbon cycle. This study aimed to characterize the regional-scale responses and adaptations of different vegetation categories to drought changes and the spatiotemporal characteristics of WUE and associated drought factors for nine vegetation categories in Inner Mongolia, China, from 2000 to 2020. This study estimated drought, the association between drought and eWUE among varying vegetation categories, and the differences in eWUE between the drought stage and the post-drought stage by analyzing the spatiotemporal variations in eWUE of different vegetation categories based on MODIS ET (evapotranspiration), GPP (gross primary productivity), and temperature vegetation drought index data. The results illustrated the following: (1) the multi-year mean eWUE from 2000 to 2020 was 1.03g·m-2·mm-1, with an overall significantly increasing trend of 0.008g·m-2·mm-1 and eWUE decreasing from northeast to southwest. (2) The rank of vegetation types in Inner Mongolia according to multi-year mean eWUE was evergreen coniferous forest > savanna > evergreen broadleaf forest > forested grassland > farmland > deciduous broadleaf forest > mixed forest > closed scrub > grassland. All vegetation categories illustrated an increasing trend in eWUE over time. (3) eWUE was inversely associated with drought in the drought stage and a clear effect of drought legacy was identified in which harsh drought impacted the eWUE of the ecosystem, whereas eWUE was positively associated with drought. (4) The eWUE values of ecosystems increased significantly after drought, indicating that ecosystems that are adapted to drought show high capacity to recovery from drought stress.