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

improved forecast systems. Many of the functional interactions within GEWEX are summarized in Fig. 2 . This GEWEX special issue of the Journal of Hydrometeorology documents some of the most recent scientific contributions to GEWEX objectives and to our understanding of the large-scale hydrometeorological system. Precipitation is considered in the first section because of its role as the driver for land surface hydrology and for determining the distribution of the world’s renewable water resources

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Ana M. B. Nunes and John O. Roads

1. Introduction Many studies have focused on the adjustment of moisture and divergence analyses (e.g., Krishnamurti et al. 1984 , 1988 , 1991 ; Donner 1988 ; Heckley et al. 1990 ; Puri and Miller 1990 ; Puri and Davidson 1992 ; Aonashi 1993 ; Kasahara et al. 1994 ; Manobianco et al. 1994 ; Yap 1995 ; Treadon 1996 ) in order to improve precipitation forecasts. Some of these studies have used observed rain rates to directly adjust the moisture and diabatic heating profiles to

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

physics are needed to improve RCM simulation. From a hydrologic point of view, the relevance of the RCM numerical simulations depends to a large extent on the simulation’s resolutions. Unfortunately, most current RCM grid resolutions, such as those adopted by the National Weather Service River Forecasting System (NWSRFS), are coarser than the requirements for river basin models. Arguably, high-resolution RCM studies that can capture the spatial variability of hydrologic/hydroclimatic variables

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

demonstrated the importance of soil moisture initialization for climate modeling (e.g., Smith et al. 1994 ; Koster and Suarez 1995 ; Betts et al. 1996 ; Fennessy and Shukla 1999 ; Koster et al. 2004 ). In particular, Koster et al. (2004) have shown an increase in precipitation forecast skill by realistic initialization of soil moisture and other land surface state variables especially in May through July. Accumulated evidence has indicated that reductions in errors of soil moisture initialization in

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Jinwon Kim and Hyun-Suk Kang

Pyrenees: A tramontana case study. Mon. Wea. Rev. , 124 , 687 – 700 . 10.1175/1520-0493(1996)124<0687:NSOFDA>2.0.CO;2 Grubišić, V. , Vellore R. , and Huggins A. , 2005 : Quantitative precipitation forecasting of wintertime storms in the Sierra Nevada: Sensitivity to the microphysical parameterization and horizontal resolution. Mon. Wea. Rev. , 133 , 2834 – 2859 . 10.1175/MWR3004.1 Gu, Y. , Fararra J. , Liou K. , and Mechoso C. , 2003 : Parameterization of cloud

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Xi Chen, Yongqin David Chen, and Zhicai Zhang

limitations of computing power, conceptual and often lumped-parameter models mainly focus on the simulation of aggregated output (total streamflow) at the watershed outlet and usually cannot offer sufficient details and accurate estimation of water fluxes in a spatially heterogeneous domain. Although these watershed hydrological models have been widely and successfully used in flood forecasting and regional water resources planning ( Shen 1992 ; Guo et al. 1997 ; Xu and Guo 1994 ), they cannot simulate

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

discussed in section 2 . In addressing some of the challenges, we also briefly comment on the quality of some of the datasets. In particular, we have three global land precipitation datasets that can be compared. We have also performed extensive diagnostics using 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data, but we limit how many of these are presented because of problems that will become apparent. The conclusions are given in section 5 . 2. Methods and

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Guoxiong Wu, Yimin Liu, Qiong Zhang, Anmin Duan, Tongmei Wang, Rijin Wan, Xin Liu, Weiping Li, Zaizhi Wang, and Xiaoyun Liang

employed the global analyses prepared by the European Centre for Medium-Range Forecasts (ECMWF) to study the onset and interannual variability of the Asian summer monsoon in relation to land–sea thermal contrast ( Li and Yanai 1996 ), the Australian summer monsoon ( Hung and Yanai 2004 ), and its relationship with the Asian summer monsoons ( Hung et al. 2004 ). In China, in the last decade, a series of research programs have been organized to support the activities related to the World Climate Research

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