Dynamics and Vulnerability of Delta Systems - loicz

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2.3 Sea-Level Change For a given deltaic coast, changes in its elevation relative to sea level depends on three factors (Syvitski et al., in review): (1) Changes to the volume of the global ocean (Eustasy), as influenced by fluctuations in the storage of terrestrial water (e.g. glaciers, ice sheets, groundwater, lakes, and reservoirs), and fluctuations in temperature of the ocean’s surface waters (Warrick & Oerlemans 1990, Bindoff et al. 2007). Sea level is presently increasing at a rate of 1.8 to 3 mm/y under the anthropogenic influence of global warming. (2) Vertical movements of the land surface, as influenced by hydro-isostasy related to sea level fluctuation, loading due to the weight of delta deposits, glacio-isostasy related to the growth or shrinkage of nearby ice masses, tectonics, and deepseated thermal subsidence (Syvitski 2008). Isostatic changes can cause deltas to subside at rates of 1-5 mm/y. (3) Changes to the sedimentary volume of the delta, through natural compaction (�3 mm/y), accelerated compaction (�150 mm/y), and aggradation or sediment deposition onto the delta’s surface (�50 mm/y). Aggradation depends on both the rate sediment is delivered to a delta, and the amount of sediment retained on the delta during its transport across the delta surface. Climate Scenarios Temperature Change in °C Sea Level Rise in m B1 1.8 0.18 - 0.38 A1T 2.4 0.20 - 0.45 B2 2.4 0.20 - 0.43 A1B 2.8 0.21 - 0.48 A2 3.4 0.23 - 0.51 A1F1 4.0 0.26 - 0.59 Fig. 2.1: IPCC comparison of observed continental changes in temperature over the last century; blue envelop is model predictions using only natural forces, pink envelop are model predictions including anthropogenic forces. Lower panel shows the projected emissions and tabelizes the projected associated temperature changes and sea level rise for 2090-2099 as compared to 1980-1999 (Bindoff et al. 2007). 18
CS4: Rapid Caspian sea level change and the Volga Delta Irina Overeem The Volga delta is a prime example of a delta that has been subjected to rapid sea-level change. IPCC reports alarming rates of worldwide sea-level rise over the last four decades, 1,8 mm/yr over 1961-2003. Model projections of sea-level rise for the next century may amount to 6mm/yr. However, the Caspian Sea changes much more rapidly than the global oceans (100 mm/yr). Over the last century the Caspian Sea went through an entire 3 m sea level cycle. 70% of the fresh water influx to the Caspian Sea is derived from the Volga River. As a result Caspian sea-level changes show a statistically significant correlation with changes in the discharge of the Volga River. These in turn have been shown to record variations in precipitation over the Volga drainage basin, related to variations in the amount of Atlantic depressions that reach the Russian mainland. Arpe et al. (2000) showed the correlation of Caspian Sea level change with ENSO. This implies that at times of sea-level fall, water and sediment flux towards the coast is low, whereas at times of sea-level rise fluxes towards the coast are relatively high. Consequently, the Volga delta experiences extremely rapid progradation of the coastline during sealevel fall, i.e. the system shoots out into its shallow basin. This was observed in the delta between 1935 and 1951. However, during sea-level rise the delta only drowns relatively slowly because sediment input helps to keep up with the rising water levels, as can be seen from the period 1981-1989. The coastline is stable then and levees were found to aggrade despite 1,5m sea level rise (Overeem et al. 2003a, 2003b). The Volga serves as an example of a delta system in which water and sediment inputs are correlated with sea-level change, making the response to change highly asymmetric. Fig. CS4.1: Vegetation mapping in the Astrakhan Nature Reserve area of the Volga delta records the rapid shoreline changes during sea level fall and more moderate infill during sea level rise over the last century (Overeem et al. 2003a, 2003b). Sea-level change related to global warming increases delta instability. The Volga delta forms a dramatic example of a delta wandering across its delta plain under influence of the rapid sea level changes of the Caspian Sea (Case Study 4). Other deltas will be influenced in the coming century; the IPCC projected sea level will likely rise by 18-71 cm by the year 2070 with a best estimate of 19
Page 1: LAND-OCEAN INTERACTIONS IN THE COAS
Page 4 and 5: Published in Germany, 2009 by: GKSS
Page 7 and 8: Executive Summary Deltas form where
Page 9 and 10: Prolog Deltas all over the world ar
Page 11 and 12: 1 Introduction Deltas are the landf
Page 13 and 14: asin by switching and/or inundation
Page 15 and 16: The Indus River in Pakistan is one
Page 17 and 18: Fig. CS2: The evolution of the dist
Page 19: CS3: Subsidence of the Po River Del
Page 23 and 24: Deltas are probably as susceptible
Page 25 and 26: climatic characteristics resulting
Page 27 and 28: A 70% decrease in the Danube’s se
Page 29 and 30: Fig. 3.2: Villagers are building a
Page 31 and 32: consequences of changing water regi
Page 33 and 34: Ibanez et al. 1996, Day et al. 2007
Page 35 and 36: 3.4 The Importance of Extreme Event
Page 37 and 38: economically sustained based on an
Page 39 and 40: • Beyond scale, do small deltas f
Page 41 and 42: CS 10: Figure based on unpublished
Page 43 and 44: depth of flooding for 10yr, 20yr, 5
Page 45 and 46: chemical gradients and other non-li
Page 47 and 48: Indus delta or the Nile delta. Glob
Page 49 and 50: 6 References Alvarado, M. (2005): C
Page 51 and 52: Elvira, B. (1995): Conservation sta
Page 53 and 54: Osborne, P.L. (2000): Tropical ecos
Page 55 and 56: Global Planetary Change (39): 111-1

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