• Energy Research

AbstractClimatic warming has lengthened the photosynthetically active season in recent decades, thus affecting the functioning and biogeochemistry of ecosystems, the global carbon cycle and climate. Temperature response of carbon uptake phenology varies spatially and temporally, even within species, and daily total intensity of radiation may play a role. We empirically modelled the thresholds of temperature and radiation under which daily carbon uptake is constrained in the temperate and cold regions of the Northern Hemisphere, which include temperate forests, boreal forests, alpine and tundra biomes. The two‐dimensionality of the temperature‐radiation constraint was reduced to one single variable, θ, which represents the angle in a polar coordinate system for the temperature‐radiation observations during the start and end of the growing season. We found that radiation will constrain the trend towards longer growing seasons with future warming but differently during the start and end of season and depending on the biome type and region. We revealed that radiation is a major factor limiting photosynthetic activity that constrains the phenology response to temperature during the end‐of‐season. In contrast, the start of the carbon uptake is overall highly sensitive to temperature but not constrained by radiation at the hemispheric scale. This study thus revealed that while at the end‐of‐season the phenology response to warming is constrained at the hemispheric scale, at the start‐of‐season the advance of spring onset may continue, even if it is at a slower pace.

Abstract Quantifying the contributions of air temperature and precipitation changes to drought events can inform decision-makers to mitigate the impact of droughts while existing studies focused mainly on long-term dryness trends. Based on the latest Coupled Model Intercomparison Project (CMIP6), we analyzed the changes in drought events and separated the contributions of air temperature and precipitation to the risk of future drought events. We found that drought frequency, duration, severity, and month will increase in the future (56.4%, 63.5%, 82.9%, and 58.2% of the global land area in SSP245, and 58.1%, 67.7%, 85.8%, and 60.5% of the global land area in SSP585, respectively). The intermediate scenario has a similar pattern to the most extreme scenario, but low emission was found to mitigate drought risk. Globally, we found that air temperature will have a greater impact than precipitation on intensifying drought. Increasing precipitation will mitigate drought risks in some middle and high northern latitudes, whilst the trend in increasing air temperature will counter the effects of precipitation and increase the impact of droughts. Our study improves the understanding of the dynamics of future devastating drought events and informs the decision-making of stakeholders.

AbstractSlope orientation creates microclimate by modulating water and heat flux between the land surface and the atmosphere, thereby regulating vegetation growth and its response to background climate change. However, the potential asymmetry in vegetation greenness between west‐ and east‐facing slopes remains underexplored. Analyzing the normalized difference vegetation index derived from Landsat reflectances in the Tibetan Plateau (TP) grassland, we identified that west‐facing slopes were greener than east‐facing slopes in the western TP, while the opposite appeared in the eastern TP. We also detected a stronger greening trend on west‐ than east‐ facing slopes over the entire TP grassland from 1991 to 2020. These disparities result from distinct microclimates on the two contrasting slopes: west‐facing slopes tend to be wetter and colder than east‐facing slopes under similar background climate. Our findings underscore the crucial role of slope orientation in shaping vegetation greenness and its response to climate change.