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C. A. S. Coelho, D. B. Stephenson, M. Balmaseda, F. J. Doblas-Reyes, and G. J. van Oldenborgh

Abstract

This study proposes an objective integrated seasonal forecasting system for producing well-calibrated probabilistic rainfall forecasts for South America. The proposed system has two components: (i) an empirical model that uses Pacific and Atlantic sea surface temperature anomalies as predictors for rainfall and (ii) a multimodel system composed of three European coupled ocean–atmosphere models. Three-month lead austral summer rainfall predictions produced by the components of the system are integrated (i.e., combined and calibrated) using a Bayesian forecast assimilation procedure. The skill of empirical, coupled multimodel, and integrated forecasts obtained with forecast assimilation is assessed and compared. The simple coupled multimodel ensemble has a comparable level of skill to that obtained using a simplified empirical approach. As for most regions of the globe, seasonal forecast skill for South America is low. However, when empirical and coupled multimodel predictions are combined and calibrated using forecast assimilation, more skillful integrated forecasts are obtained than with either empirical or coupled multimodel predictions alone. Both the reliability and resolution of the forecasts have been improved by forecast assimilation in several regions of South America. The Tropics and the area of southern Brazil, Uruguay, Paraguay, and northern Argentina have been found to be the two most predictable regions of South America during the austral summer. Skillful rainfall forecasts are generally only possible during El Niño or La Niña years rather than in neutral years.

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D. B. Stephenson, K. Rupa Kumar, F. J. Doblas-Reyes, J-F. Royer, F. Chauvin, and S. Pezzulli

Abstract

The Indian summer monsoon rainfall is the net result of an ensemble of synoptic disturbances, many of which are extremely intense. Sporadic systems often bring extreme amounts of rain over only a few days, which can have sizable impacts on the estimated seasonal mean rainfall. The statistics of these outlier events are presented both for observed and model-simulated daily rainfall for the summers of 1986 to 1989. The extreme events cause the wet-day probability distribution of daily rainfall to be far from Gaussian, especially along the coastal regions of eastern and northwestern India. The gamma and Weibull distributions provide good fits to the wet-day rainfall distribution, whereas the lognormal distribution is too skewed. The impact of extreme events on estimates of space and time averages can be reduced by nonlinearly transforming the daily rainfall amounts. The square root transformation is shown to improve the predictability of ensemble forecasts of the mean Indian rainfall for June 1986–89.

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Alan J. Hewitt, Ben B. B. Booth, Chris D. Jones, Eddy S. Robertson, Andy J. Wiltshire, Philip G. Sansom, David B. Stephenson, and Stan Yip

Abstract

The inclusion of carbon cycle processes within CMIP5 Earth system models provides the opportunity to explore the relative importance of differences in scenario and climate model representation to future land and ocean carbon fluxes. A two-way analysis of variance (ANOVA) approach was used to quantify the variability owing to differences between scenarios and between climate models at different lead times. For global ocean carbon fluxes, the variance attributed to differences between representative concentration pathway scenarios exceeds the variance attributed to differences between climate models by around 2025, completely dominating by 2100. This contrasts with global land carbon fluxes, where the variance attributed to differences between climate models continues to dominate beyond 2100. This suggests that modeled processes that determine ocean fluxes are currently better constrained than those of land fluxes; thus, one can be more confident in linking different future socioeconomic pathways to consequences of ocean carbon uptake than for land carbon uptake. The contribution of internal variance is negligible for ocean fluxes and small for land fluxes, indicating that there is little dependence on the initial conditions. The apparent agreement in atmosphere–ocean carbon fluxes, globally, masks strong climate model differences at a regional level. The North Atlantic and Southern Ocean are key regions, where differences in modeled processes represent an important source of variability in projected regional fluxes.

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Tim Li, Abdallah Abida, Laura S. Aldeco, Eric J. Alfaro, Lincoln M. Alves, Jorge A. Amador, B. Andrade, Julian Baez, M. Yu. Bardin, Endalkachew Bekele, Eric Broedel, Brandon Bukunt, Blanca Calderón, Jayaka D. Campbell, Diego A. Campos Diaz, Gilma Carvajal, Elise Chandler, Vincent. Y. S. Cheng, Chulwoon Choi, Leonardo A. Clarke, Kris Correa, Felipe Costa, A. P. Cunha, Mesut Demircan, R. Dhurmea, Eliecer A. Díaz, M. ElKharrim, Bantwale D. Enyew, Jhan C. Espinoza, Amin Fazl-Kazem, Nava Fedaeff, Z. Feng, Chris Fenimore, S. D. Francis, Karin Gleason, Charles “Chip” P. Guard, Indra Gustari, S. Hagos, Richard R. Heim Jr., Rafael Hernández, Hugo G. Hidalgo, J. A. Ijampy, Annie C. Joseph, Guillaume Jumaux, Khadija Kabidi, Johannes W. Kaiser, Pierre-Honore Kamsu-Tamo, John Kennedy, Valentina Khan, Mai Van Khiem, Khatuna Kokosadze, Natalia N. Korshunova, Andries C. Kruger, Nato Kutaladze, L. Labbé, Mónika Lakatos, Hoang Phuc Lam, Mark A. Lander, Waldo Lavado-Casimiro, T. C. Lee, Kinson H. Y. Leung, Andrew D. Magee, Jostein Mamen, José A. Marengo, Dora Marín, Charlotte McBride, Lia Megrelidze, Noelia Misevicius, Y. Mochizuki, Aurel Moise, Jorge Molina-Carpio, Natali Mora, Awatif E. Mostafa, uan José Nieto, Lamjav Oyunjargal, Reynaldo Pascual Ramírez, Maria Asuncion Pastor Saavedra, Uwe Pfeifroth, David Phillips, Madhavan Rajeevan, Andrea M. Ramos, Jayashree V. Revadekar, Miliaritiana Robjhon, Ernesto Rodriguez Camino, Esteban Rodriguez Guisado, Josyane Ronchail, Benjamin Rösner, Roberto Salinas, Amal Sayouri, Carl J. Schreck III, Serhat Sensoy, A. Shimpo, Fatou Sima, Adam Smith, Jacqueline Spence, Sandra Spillane, Arne Spitzer, A. K. Srivastava, José L. Stella, Kimberly A. Stephenson, Tannecia S. Stephenson, Michael A. Taylor, Wassila Thiaw, Skie Tobin, Dennis Todey, Katja Trachte, Adrian R. Trotman, Gerard van der Schrier, Cedric J. Van Meerbeeck, Ahad Vazifeh, José Vicencio Veloso, Wei Wang, Fei Xin, Peiqun Zhang, Zhiwei Zhu, and Jonas Zucule
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Peter Bissolli, Catherine Ganter, Tim Li, Ademe Mekonnen, Ahira Sánchez-Lugo, Eric J. Alfaro, Lincoln M. Alves, Jorge A. Amador, B. Andrade, Francisco Argeñalso, P. Asgarzadeh, Julian Baez, Reuben Barakiza, M. Yu. Bardin, Mikhail Bardin, Oliver Bochníček, Brandon Bukunt, Blanca Calderón, Jayaka D. Campbell, Elise Chandler, Ladislaus Chang’a, Vincent Y. S. Cheng, Leonardo A. Clarke, Kris Correa, Catalina Cortés, Felipe Costa, A.P.M.A. Cunha, Mesut Demircan, K. R. Dhurmea, A. Diawara, Sarah Diouf, Dashkhuu Dulamsuren, M. ElKharrim, Jhan-Carlo Espinoza, A. Fazl-Kazem, Chris Fenimore, Steven Fuhrman, Karin Gleason, Charles “Chip” P. Guard, Samson Hagos, Mizuki Hanafusa, H. R. Hasannezhad, Richard R. Heim Jr., Hugo G. Hidalgo, J. A. Ijampy, Gyo Soon Im, Annie C. Joseph, G. Jumaux, K. R. Kabidi, P-H. Kamsu-Tamo, John Kennedy, Valentina Khan, Mai Van Khiem, Philemon King’uza, Natalia N. Korshunova, A. C. Kruger, Hoang Phuc Lam, Mark A. Lander, Waldo Lavado-Casimiro, Tsz-Cheung Lee, Kinson H. Y. Leung, Gregor Macara, Jostein Mamen, José A. Marengo, Charlotte McBride, Noelia Misevicius, Aurel Moise, Jorge Molina-Carpio, Natali Mora, Awatif E. Mostafa, Habiba Mtongori, Charles Mutai, O. Ndiaye, Juan José Nieto, Latifa Nyembo, Patricia Nying’uro, Xiao Pan, Reynaldo Pascual Ramírez, David Phillips, Brad Pugh, Madhavan Rajeevan, M. L. Rakotonirina, Andrea M. Ramos, M. Robjhon, Camino Rodriguez, Guisado Rodriguez, Josyane Ronchail, Benjamin Rösner, Roberto Salinas, Hirotaka Sato, Hitoshi Sato, Amal Sayouri, Joseph Sebaziga, Serhat Sensoy, Sandra Spillane, Katja Trachte, Gerard van der Schrier, F. Sima, Adam Smith, Jacqueline M. Spence, O. P. Sreejith, A. K. Srivastava, José L. Stella, Kimberly A. Stephenson, Tannecia S. Stephenson, S. Supari, Sahar Tajbakhsh-Mosalman, Gerard Tamar, Michael A. Taylor, Asaminew Teshome, Wassila M. Thiaw, Skie Tobin, Adrian R. Trotman, Cedric J. Van Meerbeeck, A. Vazifeh, Shunya Wakamatsu, Wei Wang, Fei Xin, F. Zeng, Peiqun Zhang, and Zhiwei Zhu
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