Modeling Floodplain Dynamics: Can the Ganges-Brahmaputra Delta Keep Up with the 21st Century Sea Level Rise?

模拟洪泛区动力学：恒河-雅鲁藏布江三角洲能跟上21世纪世纪海平面上升的步伐吗？三角洲低地容易受到海平面上升的影响，但洪泛平原最终是否会被淹没取决于控制因素的平衡：河流洪水和风暴潮影响下河流和沿海洪泛平原的沉积速率，土地沉降和海平面上升。我们提出了一个计算机模拟方法，以获得00的气候强迫对河流漫滩和沿海低地沉积速率的影响。之所以选择恒河-雅鲁藏布江流域，是因为其洪泛区沉积速率已得到充分研究。重建表明，沉积物是7000-4000年前的两倍多，当时印度夏季季风雨更强烈。最近，这一数据集已扩大到包括沉积速率的潮汐恒河三角洲的气旋影响的部分。 在气候和大气模型输出的复杂程度与沉积模型采用这种输出并模拟三角洲和海岸变化的能力之间仍然存在巨大差距。社区表面动力学建模系统（CSDMS）建模工具现在提供了软件耦合技术，我们将使用这个新的工具来连接三个现有的模型：上游河流泥沙生产模型，河漫滩沉积模型和潮汐平原海岸沉积模型。该研究旨在探讨恒河-雅鲁藏布江水系对未来海平面上升和季风强度增加、洪水和热带气旋的反应，这些都是目前在共同体气候系统模型情景中预测的。孟加拉国的恒河-雅鲁藏布江和三角洲系统在政府间气候变化专门委员会的研究中被列为世纪全球海平面上升淹没低地的主要例子。1.47亿人生活在印度和孟加拉国的三角洲，是世界上最贫穷的地区之一。包围气候模型预测，季风增强11%，导致恒河和雅鲁藏布江洪水增加。这些模型指出，季风强度的增强导致孟加拉湾出现更多的气旋。仅在目前的条件下，孟加拉国平均有20%的地区季节性地被洪水淹没，预计这一地区将变得越来越大。由于洪水和风暴，沉积物被困在河漫滩和海岸。海平面上升与河流和风暴潮洪水增加以及沉积物积累增加之间的相互作用尚未得到充分研究。在7000-4000年前，恒河系统经历了一个类似的情况，海平面上升率为0.5厘米/年，这与下一个世纪的预测率的高端相似。同时，季风强度增强，河流泥沙通量增加。从沉积物岩芯推断，这两种相反的力量平衡，维持了稳定的海岸线。古三角洲系统经受住了海平面上升20-30米的考验。拟议的研究将目前对恒河-雅鲁藏布江系统的理解整合到一个数值建模框架中，并允许探索对过去模拟的不同控制。理论实验将被用来说明河流和海岸动态的复杂的相互作用，通过开放获取的社区表面动力学建模系统（CSDMS）教育资源向公众。2012年CSDMS诊所计划（下）研究生讨论三角洲脆弱性的跨学科方面，并运行三角洲沉积模型模拟动手。讲座和建模练习都将提供给世界各地的教师。

Modeling Floodplain Dynamics: Can the Ganges-Brahmaputra Delta keep up with 21st Century Sea Level Rise? Deltaic lowlands are vulnerable to sea-level rise, but whether the floodplains will ultimately drown depends on a balance of controls: sedimentation rate in the river and coastal floodplain under the influence of river floods and storm surges, subsidence of the land, and sea-level rise. We propose a computer modeling approach to get 0a grip on the effect of climatic forcing on river floodplain and coastal lowlands sedimentation rates. The Ganges-Brahmaputra Basin has been selected because its floodplain sedimentation rates are well studied. Reconstructions show that sedimentation was more than double 7000-4000 years ago when the Indian summer monsoonal rains were more intense. Recently, this dataset has been expanded to include sedimentation rates in the cyclone-affected parts of the tidal Ganges delta. There is still a huge gap between the level of sophistication of climate and atmospheric model output, and the ability of sedimentation models to take such output and model delta and coastal change. The Community Surface Dynamics Modeling System (CSDMS) Modeling Tool now offers software coupling technology and we will use this new tool to link three existing models: a upstream river sediment production model, a floodplain sedimentation model and a tidal-plain coastal sedimentation model. The study aims at exploring the response of the Ganges-Brahmaputra river system to a future sea-level rise and increase in monsoonal intensity, flooding, and tropical cyclones that are currently predicted in Community Climate System Model scenarios. The Ganges-Brahmaputra river and delta system of Bangladesh has featured in the Intergovernmental Panel on Climate Change studies as the prime example of drowning lowlands under a globally rising sea level in the 21st century. 147 million people live in the delta in India and Bangladesh; it is one of the poorest regions in the world. Ensemble climate model scenarios predict an 11% enhanced monsoon resulting in increased flooding of the Ganges and Brahmaputra Rivers. The models point to an enhanced monsoon intensity causing more cyclones in the Bay of Bengal. An average of 20% of Bangladesh is seasonally flooded under present-day conditions alone, and this area is projected to become increasingly larger. Sediment is trapped in the both the river floodplain and the coast due to flooding and storms. The interplay between rising sea level versus increased river and storm surge flooding and increased sediment accumulation has not been well studied. At 7000-4000 years ago the Ganges system experienced an analogous scenario with sea level rise rates of 0.5 cm/yr, which is similar to the high end of the predicted rate for the next century. At the same time, the monsoonal regime was enhanced and the river sediment fluxes were high. It is inferred from sediment cores that the two opposing forces balanced and a stable coastline was maintained. The ancient delta system withstood a 20-30 m sea level rise. The proposed study integrates current understanding of the Ganges-Brahmaputra System into a numerical modeling framework, and allows the exploration of different controls for the analogue of the past. Theoretical experiments will be used to illustrate the complex interplay of river and coastal dynamics to the general public through the open-access Community Surface Dynamics Modeling System (CSDMS) Educational Resources. A CSDMS clinic in 2012 is planned for (under)graduate students to discuss transdisciplinary aspects of the vulnerability of deltas, and to run delta sedimentation model simulations hands-on. The lectures and modeling excercises will all be made available for teaching faculty worldwide.