The arid region of Northwest China and Mongolia (NCM) receives most of the precipitation in the summer. The need for a better understanding of the synoptic-scale mechanism responsible for precipitation formation is accentuated by the recent wetting trend and its implications for future hydroclimate change. By conducting a hierarchical clustering analysis on an observationally-based daily precipitation dataset, we show that there are three distinct precipitation patterns over NCM, one of which is associated with strong precipitation over the western part of the region and another over the eastern part. The corresponding large-scale circulation anomalies indicate that these strong precipitation events are triggered by the upper-tropospheric disturbances in the form of transient Rossby wave packets. Furthermore, the wetting trend is linked to more frequent strong precipitation events over the eastern NCM, suggesting that it may have been induced remotely by atmospheric circulation perturbations.

The global carbon-cycle is crucial for climate change. Desert, which has long been neglected in the global carbon-cycle, may sequester enormous volumes of CO2 and play the role of a carbon-sink. As the world’s second-largest shifting desert, the Taklimakan Desert (TD) contributes substantially to desert carbon-sinks. However, the contributions of the internal processes of the TD to its carbon-sink and the long-term trend of the carbon-sink under climate change are still unclear. This study will address this important knowledge gap. Through field observations, we found that the expansion/contraction of soil air containing CO2 caused by heat fluctuation in shifting sand, in combination with salts/alkali chemistry dominates the release/absorption processes of CO2 in shifting sand. The mutual counteraction of these processes means that the TD shifting sand acts as a stable carbon-sink that had a CO2 annual uptake of 1.60×106 t•a-1 during 2004–2017. It suggests that global shifting deserts maybe uptake of ~2.125×108 t of CO2 per year. However, an increasing soil temperature-difference will stimulate soil air expansion of desert and release more CO2 into the atmosphere under climate change, causing the shifting sand carbon-sink decrease in the TD gradually in the future. These processes will be accelerated by positive feedback effect under climate change and enhance regional warming. These conclusions are very important for re-recognizing the status of deserts in the carbon-cycle, narrowing the gap in the missing carbon-sink and assessing the global carbon-cycle.

As rapid warming and consequent glaciers retreat across the Tibetan Plateau (TP), the problem about whether or not atmospheric water supply could alleviate the depletion of surface water storage need to be examined. Long-term changes of atmospheric water vapor balance across the TP is investigated by the ERA5 reanalysis from 1979 to 2018.Annual accumulated precipitation, water vapor convergence and evaporation generally keep an equilibrium but with different long-term variation trends: 0.68mm/a, 0.68mm/a and -0.18mm/a, respectively. Results suggest that surface water storage will not be well replenished by the water vapor transported from outside of the TP. For different regions of the TP, characteristic of water vapor balance and their long-term trends are completely different. Regions around Yarlung Zangbo Grand Canyon experiences sharp decrease in water vapor convergence and leads to decrease in precipitation. Meanwhile, evaporation keeps increasing due to the warming and melting of glaciers. Loss of surface water storage should be severe. For the source region of the Three Rivers, decrease in water vapor convergence overlaps increase in evaporations leads to no significant changes in total precipitations. Decrease in water transported from outsides brings risk to the depletion of surface water storage. Brahmaputra basin, inner TP and Qilian Mountain show significant wetting trends due to the increases in both convergence of water vapor flux and evaporation. Above regional characteristics of water vapor balances across the TP cause by inhomogeneous variation of atmospheric heat source and changes of atmospheric circulations, which need to be studied in further.