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Nandini Menon N.,Nansen Environmental Research Center India | Singh T.,Wageningen University | Pettersson L.H.,Nansen Environmental and Remote Sensing Center
Eos | Year: 2014

Coastal zones around the world are extremely vulnerable today because of the unprecedented pressures of industrial and urban development as well as climate change related devastations, such as the growing intensities of cyclonic storms, the rise in sea surface temperature, sea surges, and sea level rise. In India, where about 35% of the population lives within 100 kilometers of the coastline, fisheries are a major driver and safety net for economic development and coastal livelihoods. Coastal ecosystems are closely linked with socio-economic systems, which require carefully planned coastal zone management (CZM) actions. ©2014. American Geophysical Union. All Rights Reserved.

Jayakumar A.,Indian Institute of Tropical Meteorology | Jayakumar A.,Nansen Environmental Research Center India | Gnanaseelan C.,Indian Institute of Tropical Meteorology | Sabin T.P.,Indian Institute of Tropical Meteorology
International Journal of Climatology | Year: 2013

Sea surface temperature (SST) in the region off southern tip of India (STI, 75-83°E, 5-8°N) exhibited a prominent variability in the intraseasonal time scale (both 30-90 d and 10-30 d band) during boreal summer. Mechanisms associated with this intraseasonal variability are studied using three-dimensional ocean general circulation model (OGCM) sensitivity experiments, satellite observed outgoing longwave radiation, SST and winds for the period 1998-2007. The background oceanic structure of the STI characterized by a shallow thermocline and moderate mixed layer provided ideal conditions for strong oceanic sub-surface processes. The model mixed layer heat budget reveals that the oceanic processes such as horizontal advection and vertical processes are the dominant mechanisms in the STI region as compared with air-sea flux. Sensitivity experiments with the OGCM reveals that the ocean dynamical processes contribute to most of the intraseasonal SST variability and the wind stress contributes to 85% of the variability whereas surface flux contributes to only 15% for the 30-90 d SST variability. Higher amplitude of surface flux perturbation and its contribution to SST in the 10-30 d as compared with the 30-90 d band are evident in the model experiment and are consistent with the observational analysis. There is year-to-year variability in the relative role of horizontal and vertical processes for different intraseasonal SST events over STI. © 2012 Royal Meteorological Society.

Nair S.,Nansen Environmental Research Center India
IAHS-AISH Publication | Year: 2010

The impact of environmental changes on the hydrology of small basins is a serious challenge to the safety of water, food and energy supplies in the state of Kerala, India. Human interference and climate changes have altered the hydrology of most of the basins here, with significant impacts on all facets of life. Conservation and management practices are inadequate and implementation of projects and policies often fail because of various social, economic and political problems. An assessment of the impact of climate change and human interference on the small basins of Kerala has been carried out. Changes in water availability under a predicted change in climate have been estimated using the modified hydrological model. Sediment transport in selected basins has been analysed. A review has been made of both the existing programmes and projects for the protection and management of basins, as well as of current policies and adaptation strategies. Copyright © 2010 IAHS Press.

Joseph P.V.,Nansen Environmental Research Center India | Joseph P.V.,Cochin University of Science and Technology
Surveys in Geophysics | Year: 2014

Asian summer monsoon sets in over India after the Intertropical Convergence Zone moves across the equator to the northern hemisphere over the Indian Ocean. Sea surface temperature (SST) anomalies on either side of the equator in Indian and Pacific oceans are found related to the date of monsoon onset over Kerala (India). Droughts in the June to September monsoon rainfall of India are followed by warm SST anomalies over tropical Indian Ocean and cold SST anomalies over west Pacific Ocean. These anomalies persist till the following monsoon which gives normal or excess rainfall (tropospheric biennial oscillation). Thus, we do not get in India many successive drought years as in sub-Saharan Africa, thanks to the ocean. Monsoon rainfall of India has a decadal variability in the form of 30-year epochs of frequent (infrequent) drought monsoons occurring alternately. Decadal oscillations of monsoon rainfall and the well-known decadal oscillation in SST of the Atlantic Ocean (also of the Pacific Ocean) are found to run parallel with about the same period close to 60 years and the same phase. In the active-break cycle of the Asian summer monsoon, the ocean and the atmosphere are found to interact on the time scale of 30-60 days. Net heat flux at the ocean surface, monsoon low-level jetstream (LLJ) and the seasonally persisting shallow mixed layer of the ocean north of the LLJ axis play important roles in this interaction. In an El Niño year, the LLJ extends eastwards up to the date line creating an area of shallow ocean mixed layer there, which is hypothesised to lengthen the active-break (AB) cycle typically from 1 month in a La Niña to 2 months in an El Niño year. Indian monsoon droughts are known to be associated with El Niños, and long break monsoon spells are found to be a major cause of monsoon droughts. In the global warming scenario, the observed rapid warming of the equatorial Indian ocean SST has caused the weakening of both the monsoon Hadley circulation and the monsoon LLJ which has been related to the observed rapid decreasing trend in the seasonal number of monsoon depressions. © 2014 Springer Science+Business Media Dordrecht.

Jayaram C.,East-West Center | Kochuparambil A.J.,Nansen Environmental Research Center India | Balchand A.N.,Cochin University of Science and Technology
International Journal of Remote Sensing | Year: 2013

The interannual variability of chlorophyll concentration along the southwest coast of India is studied using remote-sensing data from SeaWiFS. The data are analysed in conjunction with satellite-measured sea surface winds. The satellite-measured chlorophyll data for a period of 10 years from 1998 to 2007 were made use of for indexing the maximum offshore extent of chlorophyll along the coast for each month. From the empirical orthogonal functional analysis of chlorophyll data, it is observed that the dominant mode is annual. Interestingly, intraseasonal variability and the influence of climatic events like El Niño are observed in the secondary principle component of the time series. The variability of chlorophyll coincided well with variability of Ekman transport all along the coast with higher chlorophyll (>1 mg m-3) when the Ekman transport is greater than 1000 kg/m/s. During the years 2005-2007, reduction in the meridional (along shore) component of wind resulted in reduction of Ekman transport, the phenomenon which leads to a decrease in chlorophyll. This is due to the reduction in the amount of nutrients that entrained to surface layers during upwelling of the southwest monsoon. The chlorophyll-a is minimum when Ekman transport is less than 0.5 kg/m/s on the normalized scale. For higher values of chlorophyll, the Ekman transport is higher, indicating the contribution of wind in enhancing the already upwelled chlorophyll production. The smaller value of R2 infers that there exist other forces as well involved in augmenting the surface chlorophyll. The enhanced knowledge on the offshore extent and the intraseasonal and interannual variability of chlorophyll can provide valuable inputs on fisheries and primary productivity for this region. © 2013 Copyright Taylor and Francis Group, LLC.

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