Global-mean sea-level rise will drive impacts and adaptation needs around the world's coasts over the 21st century and beyond. A key element in assessing these issues is the development of scenarios (or plausible futures) of local relative sea-level rise to support impact assessment and adaptation planning. This requires combining a number of different but uncertain components of sea level which can be linked to climatic and non-climatic (i.e., uplift/subsidence of coastal land) factors. A major concern remains about the possibility of significant contributions from the major Greenland and Antarctic ice sheets and this must be factored into the assessments, despite the uncertainty. This paper reviews the different mechanisms which contribute to sea-level change and considers a methodology for combining the available data to create relative (or local) sea-level rise scenarios suitable for impact and adaptation assessments across a range of sophistication of analysis. The methods that are developed are pragmatic and consider the different needs of impact assessment, adaptation planning, and long-term decision making. This includes the requirements of strategic decision makers who rightly focus on low probability but high consequence changes and their consequences. Hence plausible high end sea-level rise scenarios beyond the conventional Intergovernmental Panel on Climate Change (IPCC) range and which take into account evidence beyond that from the current generation of climate models are developed and their application discussed. Continued review and development of sea-level scenarios is recommended, starting with assimilating the insights of the forthcoming IPCC AR5 assessment.

The Ganges, Brahmaputra and Meghna (GBM) river basins occupy about 1.75 x 10 6 km 2 of the Himalayan region. More than half a billion people in Nepal, India, Bhutan and Bangladesh are directly or indirectly dependent on the water resources of the GBM rivers. These river basins are characterized by diversified climatic patterns. Analyses of trends and persistence in precipitation over these river basins are necessary for sound water resources planning. Time series of annual precipitation for each of the 16 meteorological subdivisions covering the three river basins were examined for trends using the Mann-Kendall rank statistic, Student's f-test and regression analysis, and for persistence using first order autocorrelation analysis. Results indicate that precipitation in the Ganges basin is by-and-large stable. Precipitation in one subdivision in the Brahmaputra basin shows a decreasing trend and another shows an increasing trend. One of the three subdivisions in the Meghna basin shows a decreasing trend while another shows an increasing trend. Markovian persistence is not present in the precipitation series in the Ganges basin but it is present in two common subdivisions in the Brahmaputra and Meghna basins. Tendances et persistance des précipitations des bassins des fleuves Gange, Brahmapoutre et MeghnaRésumé Les bassins des fleuves Gange, Brahmapoutre et Meghna (GBM) occupent une surface d'à peu près 1.75 x 10 6 de km 2 dans la région Himalayenne. Plus d'un demi milliard de personnes au Népal, en Inde, au Bhoutan et au Bangladesh dépendent directement ou indirectement des ressources d'eau des fleuves GBM. Les bassins de ces fleuves sont caractérisés par des contextes climatiques variés. Des analyses de tendances et de persistance des précipitations de ces bassins se sont révélées nécessaires en vue de réaliser une planification efficace des ressources en eau. Nous avons étudié les séries chronologiques des précipitations annuelles de chacune des seize sous-divisions météorologiques couvrant les trois bassins fluviaux en utilisant la statistique de Mann-Kendall, le test t de Student et l'analyse de régression ainsi que l'auto-corrélation du premier ordre pour les problèmes de persistance. Les résultats indiquent que les précipitations du bassin du Gange sont relativement stables. Les précipitations de l'une des sous-divisions du bassin du Brahmapoutre présentent une tendance décroissante alors que celles d'une autre sous-division présentent une tendance croissante. Il en est de même de deux des trois sous-divisions du bassin du Meghna. La série des précipitations du bassin du Gange ne montre aucune persistance Markovienne que l'on peut au contraire mettre en évidence sur deux sous-divisions communes aux bassins du Brahmapoutre et du Meghna.

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