Ecosystem water use efficiency (WUE) acts as an integrated functional indicator for understanding land‐atmosphere interactions. The temporal patterns in the daily variations of WUE and their underlying drivers during different seasons in alpine meadow ecosystems, which are particularly vulnerable to changing climate, still remain poorly understood in spite of increasing efforts. In this study, we investigated the potential divergence in the response of WUE to climatic and biological drivers during different seasons at two alpine meadow ecosystems in the northeastern Tibetan Plateau using continuous eddy‐covariance measurements of carbon and water fluxes between 2013 and 2015. We found that variations in CO₂ concentration exert significantly positive effects on variations in WUE in spring, but not in summer and autumn. Notably, vapor pressure deficit (VPD) overrode other factors playing a dominant role in regulating daily variations in WUE during all seasons in these alpine meadow ecosystems. Variations in VPD explained 29.5 to 52.3% of the variance in WUE between different seasons. We further showed that carbon gain and water loss processes responded divergently to different drivers; higher VPD significantly increased ecosystem evapotranspiration; whereas, variations in soil moisture and leaf area index significantly and positively affected gross primary productivity. Our findings highlighted the increasing importance of atmospheric drought in shaping land‐atmosphere interactions in alpine meadow ecosystems, particularly in a warming climate.

Growth of high-elevation forests is generally temperature-limited and thus sensitive to warming. The Tibetan Plateau has experienced fast warming rates associated with decreased summer monsoon rainfall over the last century. However, whether such warming and monsoon-induced drought could offset a potential warming-driven enhancement of forest growth has not been examined. Here, we have compiled high-elevation forest growth data at 40 sites over the monsoonal Tibetan Plateau (MTP), and combined them in a high-elevation forest growth index (HEFGI) spanning 1567–2010. Tree growth in this region was significantly and positively correlated with July–October minimum temperatures during 1950–2010 (R ² = 0.53 P < 0.001), and insignificantly coherent with soil moisture and precipitation. The HEFGI of MTP reaches its highest values from the 2000s onwards. This result suggests that the mean HEFGI of MTP has not been negatively affected by the current drying trend and responded positively to increased temperatures.

Rapid warming has led to an aggregated environmental degradation over the Tibetan Plateau (TP) in the last few decades, including accelerated glacier retreat, early snowmelt, permafrost degradation, and forest fire occurrence. Attribution of this warming in recent decades has mainly been focused on anthropogenic forcing. Yet, linkages to the Atlantic multidecadal variability (AMV), an essential part of the climate system causing decadal to centennial fluctuations of temperature, remains poorly understood for the TP, especially at long time scales. Using well-replicated tree-ring width records, we reconstructed 358 years of summer minimum temperature (MinT) of the whole TP. This reconstruction matches the recent warming signal recorded since the 1980s, and captures 63% of the variance in 1950–2005 instrumental records. A teleconnection from the North Atlantic to the TP is further identified based in observations and simulations with an atmospheric general circulation model (AGCM). We propose that half of the multidecadal variability of TP summer MinT can be explained by the AMV over the past three and a half centuries. Both observations and AGCM simulations indicate that the AMV warm phase induces a zonal dipole response in sea level pressure across the Atlantic–Eurasia region, with anomalously high surface pressure and corresponding downward atmospheric motion over the TP. We propose that the descending motion during warm AMV phases causes negative rainfall and positive temperature anomalies over the TP. Our findings highlight that the AMV plays a role in the multidecadal temperature variability over the TP.