Biomass burning (BB) has a significant influence on the Arctic environment. Here, we determined the atmospheric levels of BB-specific tracer compounds such as levoglucosan (Lev), galactosan (Gan), and mannosan (Man) in Arctic aerosols during 2010-2018. The average concentrations of Lev during the study period ranged between 0.43 and 4.15 ng m(-3). Both Lev/Man (0-30) and Man/Gan (0-3) ratios further suggested their origin from softwood/hardwood burning. The North Atlantic Oscillation (NAO) was the main driver of the Lev variability during the study period and Lev could be advected to Arctic air during the NAO was in a positive phase. Based upon the levels of Lev, black carbon (BC) generated from BB was estimated, and the corresponding radiative forcing was then calculated by Santa Barbara DISORT Atmospheric Radiative Transfer. BC has a potential warming effect in the atmosphere (+4.28 W/m(2)) while shows a cooling effect on the surface, which is equivalent to a large volcanic eruption (-3 W/m(2)). Since climate change is expected to intensify BB around the Arctic, such BC aerosols should be considered in future climate model projections.

The decreasing trend in rainfall in the last few decades over the Indo-Gangetic Plains of northern India as observed in ground-based observations puts increasing stress on groundwater because irrigation uses up to 70% of freshwater resources. In this work, we have analyzed the effects of extensive irrigation over the Gangetic Plains on the seasonal mean and intra-seasonal variability of the Indian summer monsoon, using a general circulation model and a very high-resolution soil moisture dataset created using extensive field observations in a state-of-the-art hydrological model. We find that the winter-time (November-March) irrigation has a positive feedback on the Indian summer monsoon through large scale circulation changes. These changes are analogous to a positive North Atlantic Oscillation (NAO) phase during winter months. The effects of the positive NAO phase persist from winter to spring through widespread changes in surface conditions over western and central Asia, which makes the pre-monsoon conditions suitable for a subsequent good monsoon over India. Winter-time irrigation also resulted in a reduction of low frequency intra-seasonal variability over the Indian region during the monsoon season. However, when irrigation is practiced throughout the year, a decrease in June-September precipitation over the Gangetic Plains, significant at 95% level, is noted as compared to the no-irrigation scenario. This decrease is attributed to the increase in local soil moisture due to irrigation, which results in a southward shift of the moisture convergence zone during the active phase of monsoon, decreasing its mean and intraseasonal variability. Interestingly, these changes show a remarkable similarity to the long-term trend in observed rainfall spatial pattern and low-frequency variability. Our results suggest that with a decline in the mean summer precipitation and stressed groundwater resources in the Gangetic Plains, the water crisis could exacerbate, with irrigation having a weakening effect on the regional monsoon.

Rapid climate warming has resulted in shrub expansion, mainly of erect deciduous shrubs in the Low Arctic, but the more extreme, sparsely vegetated, cold and dry High Arctic is generally considered to remain resistant to such shrub expansion in the next decades. Dwarf shrub dendrochronology may reveal climatological causes of past changes in growth, but is hindered at many High Arctic sites by short and fragmented instrumental climate records. Moreover, only few High Arctic shrub chronologies cover the recent decade of substantial warming. This study investigated the climatic causes of growth variability of the evergreen dwarf shrub Cassiope tetragona between 1927 and 2012 in the northernmost polar desert at 83 degrees N in North Greenland. We analysed climate-growth relationships over the period with available instrumental data (1950-2012) between a 102-year-long C.tetragona shoot length chronology and instrumental climate records from the three nearest meteorological stations, gridded climate data, and North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) indices. July extreme maximum temperatures (JulT(emx)), as measured at Alert, Canada, June NAO, and previous October AO, together explained 41% of the observed variance in annual C.tetragona growth and likely represent insitu summer temperatures. JulT(emx) explained 27% and was reconstructed back to 1927. The reconstruction showed relatively high growing season temperatures in the early to mid-twentieth century, as well as warming in recent decades. The rapid growth increase in C.tetragona shrubs in response to recent High Arctic summer warming shows that recent and future warming might promote an expansion of this evergreen dwarf shrub, mainly through densification of existing shrub patches, at High Arctic sites with sufficient winter snow cover and ample water supply during summer from melting snow and ice as well as thawing permafrost, contrasting earlier notions of limited shrub growth sensitivity to summer warming in the High Arctic.