Background Drought, ranking among the most catastrophically destructive natural phenomena worldwide, threatens ecological stability and agricultural sustainability through its increasing frequency and duration. Yunnan province, located at the intersection of the southwest monsoon and plateau climate systems, features complex topography and pronounced precipitation heterogeneity, making it highly vulnerable to drought. The synergistic effects of orographic diversity, monsoon variability, and intensified climate extremes have amplified hydroclimatic anomalies, positioning Yunnan as both an ecologically fragile zone and a drought-prone hotspot. Understanding its drought dynamics is thus crucial for revealing regional climate change impacts and improving ecosystem resilience.

Methods The water use efficiency of vegetation in Yunnan province was calculated based on the total primary productivity (GPP) and land evapotranspiration (ET) data of medium resolution imaging spectrometer (MODIS) from 2001 to 2020. Combined with the standardized precipitation evapotranspiration index (SPEI), Theil-Sen trend analysis and Mann-Kendall significance test were used to evaluate the spatial and temporal variation trend of vegetation water use efficiency (WUE). Pearson correlation analysis was used to reveal the coupling mechanism between WUE and climate drought.

Results 1) The average annual ET and GPP in Yunnan province were 530.88 mm and 611.08 gC/m², respectively, which decreased with the increase of altitude, with significant vertical zonality, showing a distribution pattern of high in the south and low in the north. 2) WUE had a slight downward trend from 2001 to 2020, and extreme drought years had a significant impact on WUE. The annual average WUE of Yunnan Province was 1.51 gC/(mm·m²), which had obvious spatial differentiation characteristics. The WUE was the highest in summer and the lowest in winter. 3) Among the different vegetation types, the WUE of forest was the highest, and the WUE of grassland was the lowest. The average WUE of the four vegetation types was: forest > shrub > agricultural vegetation > grassland. The WUE of the four vegetation types showed a downward trend, and the forest decreased the most. 4) The positive correlation between WUE and SPEI in Yunnan province increased with the increase of monthly time scale, and the long-time scale dominated the positive correlation.

Conclusions The spatiotemporal heterogeneity of water use efficiency (WUE), shaped by drought stress, encapsulates vegetation's adaptive strategies to water deficits through coordinated physiological and biophysical regulation. These findings establish a scientific framework for optimizing water resource allocation and targeted ecological conservation in Yunnan province, while offering critical insights into climate resilience planning and ecological security maintenance amidst increasing climatic variability.