Evapotranspiration (ET) is a crucial component of the hydrological cycle in terrestrial ecosystems, but estimating ET in mountainous regions is challenging. In this study, the performance of a generalized nonlinear formulation of the complementary principle while estimating daily ET was evaluated, and the spatial‐temporal variation of ET was analyzed across four vegetation types along an elevation gradient on Mount Gongga, Southwest China. The values of the calibrated Priestley and Taylor coefficients for each of the four sites ranged from 0.98 to 1.13. The correlation coefficients between the estimated and observed daily actual evapotranspiration for each of the four sites ranged from 0.71 to 0.92. A markedly asymmetrical complementary relationship existed among the four studied sites, and the values showed less scattered during the wet season. The annual ET rates were 779.12, 781.63, 701.77, and 625.17 mm/yr in the broadleaf forest (BLF), broadleaf and coniferous mixed forest (BCF), coniferous forest (CF), and shrub land (SL), respectively, and showed a decreasing trend of 9.72 mm per 100 m along the elevation gradient. After recalibration of the seasonal α_e values, the estimated annual ET rates increased and were closer to the observed values in BLF and BCF. The results indicate that daily ET in mountainous areas can be estimated using the generalized nonlinear formulation of the complementary relationship together with routine meteorological data alone, but seasonal changes in α_e values should be taken into consideration in forests with deciduous trees.

Climate-sensitive northern cryosphere inland waters emit greenhouse gases (GHGs) into the atmosphere, yet their total emissions remain poorly constrained. We present a data-driven synthesis of GHG emissions from northern cryosphere inland waters considering water body types, cryosphere zones, and seasonality. We find that annual GHG emissions are dominated by carbon dioxide ( 1149.2 1004.8 1307.5 teragrams of CO ₂ ; median Q 1 Q 3 ) and methane ( 14.2 10.1 18.5 teragrams of CH ₄ ), while the nitrous oxide emission ( 5.4 − 1.4 12.2 gigagrams of N ₂ O) is minor. The annual CO ₂ –equivalent (CO ₂ e) GHG emissions from northern cryosphere inland waters total 1.5 1.3 1.8 or 2.3 1.8 2.8 petagrams of CO ₂ e using the 100- or 20-year global warming potentials, respectively. Rivers emit 64% more CO ₂ e GHGs than lakes, despite having only one-fifth of their surface area. The continuous permafrost zone contributed half of the inland water GHG emissions. Annual CO ₂ e emissions from northern cryosphere inland waters exceed the region’s terrestrial net ecosystem exchange, highlighting the important role of inland waters in the cryospheric land-aquatic continuum under a warming climate.

Permafrost thawing over the Tibetan Plateau (TP) is a consequence of climatic warming, which will change local hydrological processes remarkably. Evapotranspiration (ET) is an important local hydrological process indicator that needs to be well quantified. Several methods have been applied to estimate the ET. However, energy consumed by thawing was neglected in ET estimation on TP. Here a simple but effective method was introduced to represent the energy consumption due to ice phase changes in the generalized nonlinear complementary principle. Our method improved ET estimation by 4.60–106.67% in the nonlinear complementary model, validated at five eddy flux observation sites. With the new formulation, we analyzed the spatiotemporal patterns of ET and their driving factors during 1961–2014. The spatial averaged ET was 294.21 mm/year and decreased from southeast to northwest areas, cocontrolled by precipitation (P_re) and net radiation (R_n); dominated by the R_n in the warm‐humid areas while by the P_re in the cold‐dry areas. The temporal pattern of ET over the TP showed an increasing trend during 1961–2014, with a rate of 0.38 mm/year. The variations in air temperature (T_air) and R_n could explain 79.1% of the temporal variations in ET over the TP during the past 54 years, indicating atmosphere demand is the dominant factor on ET temporal variation. We also found that permafrost thawing accelerated the ET increases in the last 15 years over the transitional permafrost and seasonal permafrost areas, suggesting that degradation and ablation of permafrost under climatic changes will lead to accelerated ET.

Water use efficiency (WUE) provides vital information about the carbon‐water coupling relationship of a terrestrial ecosystem. Understanding the spatiotemporal variability and driving factors of the Tibetan Plateau (TP) WUE can facilitate the prediction of the response of the carbon‐water process in the TP to climate change. We used a land surface model to investigate spatiotemporal changes in WUE and the responses to environmental factors, such as atmospheric CO₂ concentration and climate and land use change. Our results suggest that the average annual TP WUE was 0.38 g C kg⁻¹ H₂O and that this variable tended to increase at a rate of 0.001 g C kg⁻¹ H₂O year⁻¹ during the period of 1979–2010. Changes in atmospheric CO₂ concentration caused a significant increase in the rate of WUE change (i.e., 0.00051 g C kg⁻¹ H₂O year⁻¹); these changes were also found to most significantly contribute to WUE increase in the TP and account for approximately 51% of the WUE fluctuation. Increasing temperature was found to result in a decreasing WUE (rate: −0.00028 g C kg⁻¹ H₂O year⁻¹). Regarding results on vegetation type, forested areas had the highest WUE (i.e., 0.88 g C kg⁻¹ H₂O) and the highest rate of WUE change (i.e., 0.004 g C kg⁻¹ H₂O year⁻¹), whereas the lowest WUE (i.e., 0.26 g C kg⁻¹ H₂O) was found in steppe and alpine vegetation areas. Although all other vegetation types were associated with increasing WUE, there was no significant change in the WUE of steppe areas. The main factors influencing WUE fluctuation for different vegetation types were found to be atmospheric CO₂ concentration and temperature change.