Closing the Global Water Cycle in Fully-Coupled Climate System Models: Terrestrial Hydrology and River Transport for the NCAR CSM Land Component

ATM-9617980 ATM-9707953 ATM-补充件UCAR CA Famiglietti，James Vorosmarty，Charles Schimel，德克萨斯大学大卫大学新汉普郡大气研究中心在全耦合气候系统模式中关闭全球水循环：NCAR CSM陆地组成部分的陆地水文学和河流输送全球水文循环在地球气候的相互作用中发挥着核心作用。然而，目前水循环在全球气候机制中的表现不足以恰当地描述其在气候系统中的重要作用和相互作用。一个关键的缺点是，全球水循环不是封闭的，因此陆地和海洋仍然是不耦合的，即大陆的河流径流没有作为海洋的输入。这项研究的目的是通过将横跨大陆的水的水平运输(即河流运输)纳入其陆地部分，从而结束NCAR正在开发的CSM的全球水文循环。网格尺度的地表参数化将与次网格尺度的径流生成算法和全球河流网络的显式表示相结合，以准确地将河流从大陆流向海洋。我们将这种耦合的陆地参数化-次网格算法-河流输送方案称为全球陆地水文模式(GLHM)。这项工作的范围包括开发和测试全球水文学模型，该模型全面模拟了水在大陆和地表的循环；将该模型与综合水文学模型相结合，将陆地和海洋连接起来；以及利用综合水文学模型提高我们对全球水文循环在地球气候系统中的作用的预测性理解。具体的近期目标是：根据现有的或简化的模式组件开发全球水灾监测系统的原型；测试全球水灾监测系统原型再现观测到的大陆水文气候学的能力；以及进行初步的耦合模式试验，以确定关闭全球水循环对全球水灾监测系统模拟的影响。这项工作对NCAR(或任何其他)CSM努力的具体贡献包括：由于水循环关闭而保持淡水平衡模拟；计算大陆边缘物理上真实的河流过程线，以输入海洋、海冰，以及后来的生物地球化学输送模型；能够模拟被淹没的泛滥平原的亚网格土壤水分分布和亚网格部分，两者都与网格尺度的水、能量和生物地球化学通量的产生密切相关；改进了验证CSM性能的能力，因为径流是陆地表面通量中最可观察和最好记录的；以及一个了解全球水循环及其在地球气候系统内复杂相互作用的改进框架。这是首次尝试协调努力，建立一种最先进的GLHM，明确解决陆地水的垂直和水平循环，以达到关闭CSMS全球水循环的特定目的。

Abstract ATM-9617980 ATM-9707953 ATM-Supplement UCAR CA Famiglietti, James Vorosmarty, Charles Schimel, David University of Texas University of National Center for New Hampshire Atmospheric Research Closing the Global Water Cycle in Fully-Coupled Climate System Models: Terrestrial Hydrology and River Transport for the NCAR CSM Land Component The global hydrological cycle plays a central role in the interactive functioning of the Earth's climate. However, the current representation of the hydrological cycle in GCMs is inadequate to properly characterize its important role and interactions within the climate system. A critical shortcoming is that the global water cycle is not closed so that the land and oceans remain uncoupled, i.e. river runoff from the continents is not added as an input to the oceans. The purpose of this research is to close the global hydrological cycle in the CSM under development at NCAR by incorporating horizontal transport of water across the continents (i.e river transport) into its land component. A grid-scale land surface parameterization will be coupled to algorithms for subgrid-scale runoff generation and an explicit representation of global river networks to accurately route river flow across the continents to the oceans. We refer to this coupled land parameterization - subgrid algorithm - river transport scheme as a Global Land Hydrology Model (GLHM). The board scope of this work includes the development and testing of a GLHM which comprehensively models the cycling of water over and through the continental and surfaces; coupling this model to the CSM to link the land and the oceans; and using the CSM to improve our predictive understanding of the role of the global hydrological cycle in the Earth's climate system. Specific near-term objectives are to: develop a prototype version of the GLHM from existing or simplified model components; test the ability of the prototype GLHM to reproduce observed continental hydroclimatology; and to perform initial coupled model experiments to determine the effect of closing the global water cycle on CSM simulations. Specific contributions of this work to the NCAR (or any other) CSM effort include: conservation of fresh water balance simulation due to water cycle closure; computation of physically realistic river hydrographs along continental margins for input into ocean, sea ice, and later, biogeochemical transport models; the ability to simulate subgrid soil moisture distributions and subgrid fractions of inundated floodplain, both of which are intimately linked to the generation of grid-scale water, energy, and biogeochemical fluxes; an improved ability to validate CSM performance since streamflow is the most observable and well documented of the land surface fluxes; and an improved framework for understanding the global water cycle and its complex interactions within the Earth's climate system. This is the first attempt at a coordinated effort to build a state- of-the-science GLHM that explicitly resolves the vertical and horizontal circulation of terrestrial water for the specific purpose of closing the global water cycle in CSMs.