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Changes in climate extremes over major river basins of India
No full textTemporal changes in the extreme rainfall and temperature characteristics of major river basins on a daily time scale are examined using high-resolution gridded daily rainfall (1951–2014) and temperature (1951–2013) data sets. Trend analysis is carried out to examine the temporal changes in the frequency, area covered and intensity of the extreme rainfall and temperature events. Rainfall of 10 cm during southwest monsoon season (JJAS), maximum temperature of 40 °C during summer season (MAM) and minimum temperature of 10 °C during the winter season (DJF) have been used as the thresholds to define the extreme weather events of rainfall and temperature data in these river basins. Analysis indicates that during monsoon season zero rainfall days are increasing in all the river basins except some parts of the Krishna and Peninsular river basins. River basins located in the central parts of India show significant increase in the area covered by the heavy rainfall episodes and their intensity. Substantial rise in the monthly maximum temperatures is seen in the Krishna, Peninsular and West Coast river basins. Frequency, area coverage and intensity of hot days during summer season are increasing significantly in the Krishna and Peninsular river basins, while no substantial change has been observed for cold days during winter season in any river basins of the study
The Status of the Marine Fisheries of West Bengal Coast of the Northern Bay of Bengal and Its Management Options: A Review
No full textMarine fishery is one of the most important sectors for both economic and social development of the country. The whole coast of West Bengal was surveyed from July 2010 to August 2012 for acquiring data on marine fishing. The secondary data were also collected from various government departments and non-government organizations. After compiling all the data a clear picture of marine fisheries in the coastal region of West Bengal was emerged. Arius spp. has the height percentage (15.16) and Yellow Fin Tuna has the lowest percentage (0.06) of landing in West Bengal coast during 2006–2012. Bombay duck and Hairtail Ribbon fish landing shows a decreasing tendency in these 7 years. As the number of mechanically powered boats are increasing in recent years, the total marine fish landing from West Bengal coast is remained more or less static. Therefore, the catch per unit effort has declined significantly in recent years (r = 0.77). So, immediate remedial measures should be taken to manage sustainably, the marine fishery sector of West Benga
Progress of Indian summer monsoon onset and convective episodes over Indo-Pacific region observed during 2009-2014
Get PDFSummer monsoon onset progress from the oceanic region of Southeast Bay of Bengal / Andaman Sea (Oceanr) up to extreme southwestern part of India (Kerala) for the years 2009 to 2014 is investigated. Synoptic weather information, INSAT/KALPANA-1 as well as cloud imageries archived from Dundee Satellite Receiving Station for May and early June for these years are used in the analysis. Upper-air reanalyzed winds from NCEP/NCAR and OLR data archived
through NOAA satellites are also used. During the study period, the dates of monsoon onset as well as the time required for the advancement of onset from Oceanr to Kerala have shown a large variation. An attempt is made to investigate the causes for such variations. The results indicate that intense disturbances which formed over north Indian Ocean in 2009, 2010, 2013 and 2014 and over west-north Pacific Oceanic region in 2011 and 2012 have contributed for the same. Analysis is carried out, limiting its focus to bring out the role of these convective events in the observed variation of onset timing and its progress by taking case to case review of these events and bringing out their influence through synoptic analysis. Utility of this information in prediction of the progress of Indian summer monsoon onset is also brought out
Prediction of summer monsoon rainfall over India and its homogeneous regions
No full textThe coherent regions for various fields such as sea level pressure, temperature, geopotential height and zonal wind anomalies at the surface, 850, 500 and 200 hPa levels in pre-monsoon months (January through May) and seasons (winter, spring) have been identified by applying the shared nearest neighbour algorithm. The fields over the corresponding cluster regions could be possible predictors for Indian summer monsoon rainfall as well as the rainfall over various homogeneous regions of India. The time series have been constructed by averaging the parameters over the respective clusters. The relationship between these time series and the summer monsoon rainfall over India and its well-defined homogeneous regions over India, (northwest India, central northeast India, northeast India, west central India and peninsular India), has been examined during the positive and negative phases of effective strength index tendency using the simple technique of multiple regression. Along with the linear relationship, the non-linear relationships between the cluster parameters and the seasonal rainfall have also been considered. Independent cluster parameters have been selected by cross-validation procedure and the performance of each predictive model is tested. The extreme yearly rainfall departures over India are qualitatively well predicted by the model. Also, the unprecedented droughts over India in 2002 and 2009, where all earlier models have failed to forecast, are well predicted by the present model. The performances of models for summer monsoon rainfall prediction over homogeneous regions of India are convincing
Evolution of the impacts of the 2009–10 El Niño and the 2010–11 La Niña on flash rate in wet and dry environments in the Himalayan range
No full textImpacts of the 2009–2010 El Niño and the 2010–2011 La Niña events on the lightning activity in the climatologically dry and moist regions of the Himalayan range are studied from the 18-year (1995–2012) data obtained from the combination of Optical Transient Detector and Lighting Imaging Sensors on the TRMM satellite. Average flash rates in both regions are higher than the 18-year normal during both El Niño and La Niña events. Our results suggest that the impacts of El Niño and La Niña need to be examined season-wise separately in moist and dry regions. During El Niño, the flash rate increases from the month of February into the pre-monsoon season but has no significant effect in the monsoon and post-monsoon seasons in the moist region. On the contrary, flash rate does not change during the pre-monsoon but is higher than normal in the monsoon and lower than normal in post-monsoon season in the dry region. During La Niña, it does not change from its normal value in any season of the moist region and even in pre-monsoon season of dry region. However, it is higher than normal in the monsoon and post-monsoon seasons of the dry region. In the dry region, while flash rate is highly correlated with convective available potential energy (CAPE), surface temperature, and convective rain fall, it is highly correlated only with CAPE in the moist region during La Niña events. Moist convection and aerosols appear to be important parameters for production of lightning in moist and dry regions, respectively. Progress of the monsoon current dramatically affects the lightning activity in both moist and dry regions
Differential bleaching of corals based on El Niño type and intensity in the Andaman Sea, southeast Bay of Bengal
No full textThe Andaman coral reef region experienced mass bleaching events during 1998 and 2010. The purpose of this study is to investigate the role of the El Niño in the coral reef bleaching events of the Andaman region. Both Niño 3.4 and 3 indices were examined to find out the relationship between the mass bleaching events and El Niño, and correlated with sea surface temperature (SST) anomalies in the Andaman Sea. The result shows that abnormal warming and mass bleaching events in the Andaman Sea were seen only during strong El Niño years of 1997–1998 and 2009–2010. The Andaman Sea SST was more elevated and associated with El Niño Modoki (central Pacific El Niño) than conventional El Niño (eastern Pacific El Niño) occurrences. It is suggested that the development of hot spot patterns around the Andaman Islands during May 1998 and April–May 2010 may be attributed to zonal shifts in the Walker circulation driven by El Niño during the corresponding period
Reconstruction of heat index based on tree-ring width records of western Himalaya in India
No full textTo study climate variability/change, the tree-ring width index chronologies of two species (Cedrus deodara and Pinus roxburghii) of the western Himalaya was determined. The first principal component (PC1) prepared using the three-site tree-ring width chronologies of the western Himalaya was found to be negatively correlated with the heat index and positively with the Palmer Drought Severity Index (PDSI) and moisture index from February to May as representative of the regional climate. The correlation coefficient of PC1 with the heat index, PDSI, and moisture index for the period 1901–1988 was estimated to be −0.60, 0.37, and 0.59, respectively, which were highly significant at 0.1% level. The result shows that increasing the heat index may enhance transpiration and evaporation over the western Himalaya, which may cause insufficient moisture at the root zone of the trees. Based on the tree-ring data, the heat index of spring season (February–May) was reconstructed back to AD 1839. The reconstructed heat index showed the longest warm periods during 1952–1963 and 1966–1976 in the 20th century
Variability in AIRS CO2 during active and break phases of Indian summer monsoon
No full textDue to human activities, the atmospheric concentration of Carbon Dioxide (CO2) has been rising extensively since the Industrial Revolution. Indian summer monsoon (ISM) has a dominant westerly component from ocean to land with a strong tendency to ascend and hence may have role in CO2 distribution in lower and middle troposphere over Indian sub-continent. A substantial component of ISM variability arises from the fluctuations on the intra-seasonal scale between active and break phases which correspond to strong and weak monsoon circulation. In view of the above, an attempt is made in this study to examine the AIRS/AQUA satellite retrieved CO2 distribution in response to atmospheric circulation with focus on active and break phase. Correlation analysis indicates the increase in AIRS CO2 linked with strong monsoon circulation. Study also reveals that anomalous circulation pattern during active and break phase show resemblance with high and low values of AIRS CO2. Homogeneous monsoon regions of India show substantial increase in CO2 levels during active phase. Hilly regions of India show strong contrast in CO2 and vertical velocity during active and break phases
Monsoon-extratropical circulation interactions in Himalayan extreme rainfall
No full textExtreme precipitation and flood episodes in the Himalayas are oftentimes traced to synoptic situations involving connections between equatorward advancing upper level extratropical circulations and moisture-laden tropical monsoon circulation. While previous studies have documented precipitation characteristics in the Himalayan region during severe storm cases, a comprehensive understanding of circulation dynamics of extreme precipitation mechanisms is still warranted. In this study, a detailed analysis is performed using rainfall observations and reanalysis circulation products to understand the evolution of monsoon-extratropical circulation features and their interactions based on 34 extreme precipitation events which occurred in the Western Himalayas (WEH) during the period 1979–2013. Our results provide evidence for a common large-scale circulation pattern connecting the extratropics and the South Asian monsoon region, which is favorable for extreme precipitation occurrences in the WEH region. This background upper level large-scale circulation pattern consists of a deep southward penetrating midlatitude westerly trough, a blocking high over western Eurasia and an intensifying Tibetan anticyclone. It is further seen from our analysis that the key elements of monsoon-midlatitude interactions, responsible for extreme precipitation events over the WEH region, are: (1) midlatitude Rossby wave breaking, (2) west-northwest propagation of monsoon low-pressure system from the Bay of Bengal across the Indian subcontinent, (3) eddy shedding of the Tibetan anticyclone, (4) ageostrophic motions and transverse circulation across the Himalayas, and (5) strong moist convection over the Himalayan foothills. Furthermore, high-resolution numerical simulations indicate that diabatic heating and mesoscale ageostrophic effects can additionally amplify the convective motions and precipitation in the WEH region
C-band RISAT-1 imagery for geospatial mapping of cryospheric surface features in the Antarctic environment
No full textCryospheric surface feature classification is one of the widely used applications in the field of polar remote sensing. Precise surface feature maps derived from remotely sensed imageries are the major requirement for many geoscientific applications in polar regions. The present study explores the capabilities of C-band dual polarimetric (HH & HV) SAR imagery from Indian Radar Imaging Satellite (RISAT-1) for land cryospheric surface feature mapping. The study areas selected for the present task were Larsemann Hills and Schirmacher Oasis, East Antarctica. RISAT-1 Fine Resolution STRIPMAP (FRS-1) mode data with 3-m spatial resolution was used in the present research attempt. In order to provide additional context to the amount of information in dual polarized RISAT-1 SAR data, a band HH+HV was introduced to make use of the original two polarizations. In addition to the data calibration, transformed divergence (TD) procedure was performed for class separability analysis to evaluate the quality of the statistics before image classification. For most of the class pairs the TD values were comparable, which indicated that the classes have good separability. Fuzzy and Artificial Neural Network classifiers were implemented and accuracy was checked. Nonparametric classifier Support Vector Machine (SVM) was also used to classify RISAT-1 data with an optimized polarization combination into three land-cover classes consisting of sea ice/snow/ice, rocks/landmass, and lakes/waterbodies. This study demonstrates that C-band FRS1 image mode data from the RISAT-1 mission can be exploited to identify, map and monitor land cover features in the polar regions, even during dark winter period. For better landcover classification and analysis, hybrid polarimetric data (cFRS-1 mode) from RISAT-1, which incorporates phase information, unlike the dual-pol linear (HH, HV) can be used for obtaining better polarization signatures