Estimation of Sediments in Rengali Reservoir, Odisha (India) Using Remote Sensing

Reservoir sedimentation is a regular process and sequential path of sedimentation in reservoirs comprising of erosion, entrainment, transference, deposition and compaction of dregs carried into artificial lakes formed behind the dams. India houses 5334 large dams in function (2329 numbers before 1980) and 411 dams are in pipeline. The Rengali dam, functioned from 1984, that traps 50% of the total sediment load of the Brahmani River continues to thwart the growth and buffering of the Brahmani delta. Remote sensing (RS) and Geographical Information System (GIS) have emerged as powerful tools to create spatial inventory on Hydro-Bio-geo resources and the state of the environment. The RS/GIS and process-based modelling employed in spatial and dynamic assessment of loss in live storage of the reservoir by developing contour, aspect and slope map by using data received from LANDSAT sources. The sedimentation of the Rengali reservoir (functional from 1984) studied for three decades 1990-2000; 2000-2010 and 2010- 2020 by constructing contour, aspect and water spread area maps by using web based data (satellite downloads). The web based water spread area data analysed by GIS tool for integration, spatial analysis, and visual presentations. The results revealed that the decadal rate of sedimentation of Rengali reservoir is reducing with age. An appropriate reservoir operation and management system as per defined protocols considering sediment related problems is essential for controlling the ageing processes that may diminish the safety and shorten the reservoir life.

Perspectives on future sea ice and navigability in the Arctic

The retreat of sea ice has been found to be very significant in the Arctic under global warming. It is projected to continue and will have great impacts on navigation. Perspectives on the changes in sea ice and navigability are crucial to the circulation pattern and future of the Arctic. In this investigation, the decadal changes in sea ice parameters were evaluated by the multi-model from the Coupled Model Inter-comparison Project Phase 6, and Arctic navigability was assessed under two shared socioeconomic pathways (SSPs) and two vessel classes with the Arctic transportation accessibility model. The sea ice extent shows a high possibility of decreasing along SSP5-8.5 under current emissions and climate change. The decadal rate of decreasing sea ice extent will increase in March but decrease in September until 2060, when the oldest ice will have completely disappeared and the sea ice will reach an irreversible tipping point. Sea ice thickness is expected to decrease and transit in certain parts, declining by −0.22 m per decade after September 2060. Both the sea ice concentration and volume will thoroughly decline at decreasing decadal rates, with a greater decrease in volume in March than in September. Open water ships will be able to cross the Northern Sea Route and Northwest Passage between August and October during the period from 2045 to 2055, with a maximum navigable percentage in September. The time for Polar Class 6 (PC6) ships will shift to October–December during the period from 2021 to 2030, with a maximum navigable percentage in October. In addition, the central passage will be open for PC6 ships between September and October during 2021–2030.

Evolution of Antarctic ozone in September–December predicted by CCMVal-2 model simulations for the 21st century

Chemistry-Climate Model Validation phase 2 (CCMVal-2) model simulations are used to analyze Antarctic ozone increases in 2000–2100 during local spring and early summer, both vertically integrated and at several pressure levels in the lower stratosphere. Multi-model median trends of monthly zonal mean total ozone column (TOC), ozone volume mixing ratio (VMR), wind speed and temperature poleward of 60° S are investigated. Median values are used to account for large variability in models, and the associated uncertainty is calculated using a bootstrapping technique. According to the trend derived from the twelve CCMVal-2 models selected, Antarctic TOC will not return to a 1965 baseline, an average of 1960–1969 values, by the end of the 21st century in September–November, but will return in ~2080 in December. The speed of December ozone depletion before 2000 was slower compared to spring months, and thus the decadal rate of December TOC increase after 2000 is also slower. Projected trends in December ozone VMR at 20–100 hPa show a much slower rate of ozone recovery, particularly at 50–70 hPa, than for spring months. Trends in temperature and winds at 20–150 hPa are also analyzed in order to attribute the projected slow increase of December ozone and to investigate future changes in the Antarctic atmosphere in general, including some aspects of the polar vortex breakup.

Disturbance regimes of hemlock-dominated old-growth forests in northern New York, U.S.A.

Old-growth forests often have complex, uneven age structures reflecting both the long time elapsed since a major disturbance and the periodic formation of small canopy gaps. I established 12 plots of 0.1 ha in four areas of old growth to describe the stand-scale disturbance regime of forests dominated by eastern hemlock (Tsuga canadensis (L.) Carrière) in northern Adirondack Park, N.Y., U.S.A. I analyzed radial-increment patterns of cores from all canopy trees (398 trees in total) on each plot to determine the date of accession to canopy for each tree. Major growth releases indicated disturbance events that resulted in either gap origin (16% of events) or release from suppression (82% of events). The average decadal rate of disturbance for all plots and decades of the 130-year period from 1850 to 1979 is 4.8–5.4% of current exposed crown area. The average canopy-tree residence time is 184–211 years. The stand-scale disturbance regimes in these Adirondack forests are similar to those of hemlock–hardwood forests in Wisconsin, Michigan, Pennsylvania, and New York. These hemlock-dominated old-growth stands appear to be in quasi-equilibrium when viewed together over 13 decades.