Compound warm events exert profound impacts on environment, health, and socioeconomics. A recent study indicated a shift or transition from warm-dry events (WDEs), common in non-ice-covered areas, to warm-wet events (WWEs) in ice-covered zones. Utilizing ERA5 reanalysis data, this study determined the duration and frequency of WDEs and WWEs across ice-covered and non-ice-covered regions. A comprehensive analysis uncovers the physical mechanisms responsible for this shift and attributes it to the weakening of land-atmosphere interaction caused by ice-cover, which inhibits soil moisture feedback and reduces the intensity and duration of warm events in ice-covered areas. Both WDEs and WWEs are associated with high-pressure systems (HPs). WDEs, situated directly beneath HPs, intensify due to adiabatic warming from subsidence motions. Conversely, WWEs, located beneath the poleward fringes of HPs, emerge from advective warming and moistening associated with poleward intrusions of warm-moist air.

A document by Josefine Axelsson. Click on the document to view its contents.

Total evaporation from the vast terrain of the Tibetan Plateau (TP) may strongly influence downwind regions. However, the ultimate fate of this moisture remains unclear. This study tracked and quantified TP-originating moisture. The results show that the TP moisture participation in downwind regions’ precipitation is the strongest around the eastern edge of the TP and then weakens gradually toward the east. Consequently, TP moisture in the composition of precipitation over the central-eastern TP is the largest of over 30%. 44.9-46.7% of TP annual evaporation is recycled over the TP, and about 2/3 of the TP evaporation is reprecipitated over terrestrial China. Moisture cycling of TP origin shows strong seasonal variation, with seasonal patterns largely determined by precipitation, evaporation and wind fields. High levels of evaporation and precipitation over the TP in summer maximize local recycling intensity and recycling ratios. Annual precipitation of TP origin increased mainly around the northeastern TP during 2000-2020. This region consumed more than half of the increased TP evaporation. Further analyses showed that changes in reprecipitation of TP origin were consistent with precipitation trends in nearby downwind areas: when intensified TP evaporation meets intensified precipitation, more TP moisture is precipitated out. The model estimated an annual precipitation recycling ratio (PRR) of 26.9-30.8% in forward moisture tracking. However, due to the non-closure issue of the atmospheric moisture balance equation, the annual PRR in backward tracking can be ~6% lower.

Permafrost-affected ecosystems are prone to warming and thawing, which can increase the availability of subsurface nitrogen (N) with consequences for otherwise N-limited tundra vegetation. Here, we show that the upper permafrost of the Tibetan Plateau is subject to thawing and that the upper permafrost zone is rich in ammonium. Furthermore, a five-year 15N tracer experiment showed that long-rooted plant species were able to utilize 15N-labeled N at the permafrost table and far below the main root zone. A 20 years survey is used here to document that long-rooted plant species had a competitive advantage at sites subject to warming and that both plant composition and growth were significantly correlated with permafrost thawing and changes in nitrogen availability. Our experiment documents a clear feedback mechanism of climate warming, which releases plant–available N favoring long-rooted plants and explains important changes in plant composition and growth across sites on the Tibetan Plateau.

Mesoscale convective systems (MCSs) have been identified as an important source of precipitation in the Tibetan Plateau (TP) region. However, the characteristics and structure of MCS-induced precipitation are not well understood. Infrared satellite imagery has been used for MCS tracking, but cirrus clouds or cold surfaces can cause misclassifications of MCS in mountain regions. We therefore combine brightness temperatures from IR imagery with satellite precipitation data from GPM and track MCSs over the TP, at the boundary of the TP (TPB) and in the surrounding lower-elevation plains (LE) between 2000 and 2019. We show that MCSs are less frequent over the TP than earlier studies have suggested and most MCSs over land occur over the Indo-Gangetic Plain (LE) and the south of the Himalayas (TPB). In the LE and TPB, MCSs have produced 10 % to 55 % of the total summer precipitation (10 % to 70 % of summer extreme precipitation), whereas MCSs over the TP account for only 1 % to 10 \% to the total summer precipitation (1 % to 30 % of the total summer extreme precipitation). Our results also show that MCSs that produce the largest amounts of convective precipitation are characterized by longevity and large extents rather than by high intensities. These are mainly located south of the TP, whereas smaller-scale convection makes a greater contribution to total and total extreme precipitation over the TP. These results highlight the importance of convective scale modeling to improve our understanding of precipitation dynamics over the TP.