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Kevin E. Trenberth, Lesley Smith, Taotao Qian, Aiguo Dai, and John Fasullo

land between the two hemispheres. Therefore, there is a need to resolve continental scales and zonal mean latitude–time sections, and these results are also presented in section 4 . The third challenge posed is to determine the interannual and longer-term variability of this cycle. This is especially an issue with nonstationary components associated with global climate change. For the most part, this aspect is taken up elsewhere. The methods and most datasets used in sections 3 and 4 are

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J. Li, X. Gao, and S. Sorooshian

hydrologic models that can accurately assess the basin’s water budget components and their variability at space and time scales. Many previous studies that include the upper Rio Grande basin have used the coupled atmosphere–land surface regional climate model (RCM) to analyze the hydroclimatic characteristics of the western mountainous region. These studies have addressed regional climate regimes ( Giorgi and Bates 1989 ; Giorgi et al. 1993 , 1994 ; Anderson et al. 2004 ; Xu et al. 2004 ; Kim and

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Richard G. Lawford, John Roads, Dennis P. Lettenmaier, and Phillip Arkin

. It is also a critical contributor to the global water cycle through its removal of water from the atmosphere and to the global energy cycle through its latent heat release. Land–atmosphere interactions on different scales, which are discussed in the second section of this special issue, determine the surface component of water and energy budgets over land surfaces, influence the predictability of precipitation, and affect the contributions of land use practices to global change. For example, the

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Scott Curtis, Ahmed Salahuddin, Robert F. Adler, George J. Huffman, Guojun Gu, and Yang Hong

rainfall is inadequate for evaluating extremes, and present an alternative methodology that yields a stronger relationship between precipitation extremes and El Niño. Interestingly, Lyon and Barnston (2005) , using a similar index to the one used by Goddard and Dilley (2005) except with a weighting to dampen large normalized anomalies at the beginning and end of dry seasons, show that the spatial extent of very wet and dry months in tropical land areas increases with extreme La Niña and El Niño

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Binayak P. Mohanty and Jianting Zhu

parameters, which are a function of soil, vegetation, topography, and other land surface properties. While the quality and availability of remotely sensed vegetation- and topography-related land surface parameters have improved significantly over the last few decades, comparable advances in global soil-related parameters at matching scales have not occurred. In fact, given that soil moisture is known to be a critical climate variable, it could be argued that our current approach of using texture

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Xubin Zeng and Aihui Wang

1. Introduction Vegetation can be characterized by its type, horizontal coverage, and vertical distribution. While vegetation types are considered by almost all land models, the treatment of vegetation horizontal coverage and vertical thickness is quite different in different land models. For instance, an annually maximum fractional vegetation cover (FVC) along with seasonally variable leaf area index (LAI) is used in the Community Land Model version 3 (CLM3; Oleson et al. 2004 ), while

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Ana M. B. Nunes and John O. Roads

are much larger than in the temperature (see also Puri and Davidson 1992 ; Hou et al. 2000 ; Falkovich et al. 2000 ). This PA methodology not only improves atmospheric characteristics but also improves the surface hydrology and may eventually prove to be superior to the uncoupled methodology used for the Global Soil Wetness Project (GSWP; Dirmeyer et al. 1999 ), the Global Land Data Assimilation System (GLDAS; Rodell et al. 2004 ), and the North American Land Data Assimilation System (NLDAS

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Song Yang, S-H. Yoo, R. Yang, K. E. Mitchell, H. van den Dool, and R. W. Higgins

deep and shallow convection. The scheme for explicitly predicted cloud water employs the scheme of Zhao and Carr (1997) . The Geophysical Fluid Dynamics Laboratory (GFDL) scheme is used for radiation. Free atmospheric turbulent exchange above the lowest model layer is via Mellor–Yamada level 2.0 ( Mellor and Yamada 1982 ), and the treatment of the surface layer and similarity functions therein is described in Chen et al. (1997) . A viscous sublayer is used over water surface. The land surface

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Xia Zhang, Shu Fen Sun, and Yongkang Xue

1. Introduction The area of frozen soil, including permafrost and seasonal frost, accounts for about 20% of the earth’s land area ( Peixoto and Oort 1992 ). Frozen soil processes in cold regions play an important role in climate change and weather forecasting ( Mölders and Walsh 2004 ; Poutou et al. 2004 ; Viterbo et al. 1999 ). For example, the freeze–thaw cycle modulates the change of both soil temperature and the overlying air temperature due to release or absorption of latent heat during

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Xi Chen, Yongqin David Chen, and Zhicai Zhang

’s Water Balance Simulation Model (WaSiM-ETH) ( Schulla and Jasper 2001 ), and HydroGeoSphere ( Therrien et al. 2004 ) have become internationally well known and gained popularity for use in applications to solve many kinds of water resources problems. MIKE SHE and WaSiM-ETH dynamically link the unsaturated zone model (Richard’s equation) and a 2D or 3D groundwater model in a numerical method that can simulate the entire land phase of the hydrologic cycle. MIKE SHE has become a more popular tool and

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