Role of Different Moisture Sources in Driving the Western Himalayan Past-glacier Advances

The fragmented pattern and the rapidly declining preservation of older glacial features/evidences limits the precision,with which glacial chronologies can be established.The challenge is exacerbated by the scarcity of datable material and limitations of dating methods.Nevertheless,the preserved glacial landforms have been fairly utilized to establish glacial chronologies from different sectors of the Indian Himalayas.The existing Himalayan glacial chrono-stratigraphies have revealed that in a single valley,past glacial advances rarely surpass four stages.Thus,local and regional glacial chronologies must be synthesized to understand glacial dynamics and potential forcing factors.This research presents an overview of glacier responses to climate variations revealed by glacial chrono-stratigraphies in the western Indian Himalayan region over the Quaternary(late).The synthesis demonstrated that,although the glacial advances were sporadic,glaciers in western Himalayas generally advanced during the Marine isotope stage(MIS)-3/4,MIS-2,late glacial,Younger Dryas(YD)and Holocene periods.The Holocene has witnessed multiple glacial advances and the scatter is significant.While previous glacial research revealed that Himalayan glaciers were out of phase with the global last glacial maximum(gLGM),weak Indian Summer Monsoon(ISM)has been implicated(ISM was reduced by roughly 20%).Recent research,however,has shown that gLGM glaciation responded to the global cooling associated with the enhanced mid-latitude westerlies(MLW).Further,the magnitude of gLGM glacier advance varied along and across the Himalayas particularly the transitional valleys located between the ISM and MLW influence.It is also evident that both the ISM and MLW have governed the late Quaternary glacial advances in the western Himalayan region.However,the responses of glaciers to ISM changes are more prominent.The insights gained from this synthesis will help us understand the dynamics of glacier response to climate change,which will be valuable for future climate modelling.

Seasonal differences in climatic controls of vegetation growth in the Beijing–Tianjin Sand Source Region of China

Launched in 2002, the Beiing–Tianjin Sand Source Control Project (BTSSCP) is an ecological restoration project intended to prevent desertification in China. Evidence from multiple sources has confirmed increases in vegetation growth in the BTSSCP region since the initiation of this project. Precipitation and essential climate variable-soil moisture (ECV-SM) conditions are typically considered to be the main drivers of vegetation growth in this region. Although many studies have investigated the inter-annual variations of vegetation growth, few concerns have been focused on the annual and seasonal variations of vegetation growth and their climatic drivers, which are crucial for understanding the relationships among the climate, vegetation, and human activities at the regional scale. Based on the normalized difference vegetation index (NDVI) derived from MODIS and the corresponding climatic data, we explored the responses of vegetation growth to climatic factors at annual and seasonal scales in the BTSSCP region during the period 2000–2014. Over the study region as a whole, NDVI generally increased from 2000 to 2014, at a rate of 0.002/a. Vegetation growth is stimulated mainly by the elevated temperature in spring, whereas precipitation is the leading driver of summer greening. In autumn, positive effects of both temperature and precipitation on vegetation growth were observed. The warming in spring promotes vegetation growth but reduces ECV-SM. Summer greening has a strong cooling effect on land surface temperature. These results indicate that the ecological and environmental consequences of ecological restoration projects should be comprehensively evaluated.

Extreme fire weather is the major driver of severe bushfires in southeast Australia

In Australia,the proportion of forest area that burns in a typical fire season is less than for other vegetation types.However,the 2019-2020 austral spring-summer was an exception,with over four times the previous maximum area burnt in southeast Australian temperate forests.Temperate forest fires have extensive socio-economic,human health,greenhouse gas emissions,and biodiversity impacts due to high fire intensities.A robust model that identifies driving factors of forest fires and relates impact thresholds to fire activity at regional scales would help land managers and fire-fighting agencies prepare for potentially hazardous fire in Australia.Here,we developed a machine-learning diagnostic model to quantify nonlinear relationships between monthly burnt area and biophysical factors in southeast Australian forests for 2001-2020 on a 0.25°grid based on several biophysical parameters,notably fire weather and vegetation productivity.Our model explained over 80%of the variation in the burnt area.We identified that burnt area dynamics in southeast Australian forest were primarily controlled by extreme fire weather,which mainly linked to fluctuations in the Southern Annular Mode(SAM)and Indian Ocean Dipole(IOD),with a relatively smaller contribution from the central Pacific El Niño Southern Oscillation(ENSO).Our fire diagnostic model and the non-linear relationships between burnt area and environmental covariates can provide useful guidance to decision-makers who manage preparations for an upcoming fire season,and model developers working on improved early warning systems for forest fires.

A comprehensive framework for seasonal controls of leaf abscission and productivity in evergreen broadleaved tropical and subtropical forests

Relationships among productivity,leaf phenology,and seasonal variation in moisture and light availability are poorly understood for evergreen broadleaved tropical/subtropical forests,which contribute 25% of terrestrial productivity.On the one hand,as moisture availability declines,trees shed leaves to reduce transpiration and the risk of hydraulic failure.On the other hand,increases in light availability promote the replacement of senescent leaves to increase productivity.Here,we provide a comprehensive framework that relates the seasonality of climate,leaf abscission,and leaf productivity across the evergreen broadleaved tropical/subtropical forest biome.The seasonal correlation between rainfall and light availability varies from strongly negative to strongly positive across the tropics and maps onto the seasonal correlation between litterfall mass and productivity for 68 forests.Where rainfall and light covary positively,litterfall and productivity also covary positively and are always greater in the wetter sunnier season.Where rainfall and light covary negatively,litterfall and productivity are always greater in the drier and sunnier season if moisture supplies remain adequate;otherwise productivity is smaller in the drier sunnier season.This framework will improve the representation of tropical/subtropical forests in Earth system models and suggests how phenology and productivity will change as climate change alters the seasonality of cloud cover and rainfall across tropical/subtropical forests.