Climatic Change DOI 10.1007/s10584-013-0844-y Large biases and inconsistent climate change signals in ENSEMBLES regional projections Marco Turco · Antonella Sanna · Sixto Herrera · Maria-Carmen Llasat · José Manuel Gutiérrez Received: 28 January 2013 / Accepted: 8 July 2013 © Springer Science+Business Media Dordrecht 2013 Abstract In this paper we analyze some caveats found in the state-of-the-art ENSEMBLES regional projections dataset focusing on precipitation over Spain, and highlight the need of a task-oriented validation of the GCM-driven control runs. In particular, we compare the performance of the GCM-driven control runs (20C3M scenario) with the ERA40-driven ones (“perfect” boundary conditions) in a common period (1961–2000). Large deviations between the results indicate a large uncertainty/bias for the particular RCM-GCM combinations and, hence, a small confidence for the corresponding transient simulations due to the potential nonlinear amplification of biases. Specifically, we found large biases for some RCM-GCM combinations attributable to RCM in-house problems with the particular GCM coupling. These biases are shown to distort the corresponding climate change signal, M. Turco (B ) CMCC (Euro-Mediterranean Centre on Climate Change), Impacts on Soil and Coasts Division, via Maiorise s.n.c., 81043, Capua CE, Italy e-mail: marco.turco@cmcc.it A. Sanna CMCC (Euro-Mediterranean Centre on Climate Change), Viale Aldo Moro 44, 40127 Bologna, Italy S. Herrera Grupo de Meteorología, Department of Applied Mathematics and Computer Science, Universidad de Cantabria (UC), Av. de los Castros s/n, Santander, 39005, Spain M.-C. Llasat University of Barcelona, Av. Diagonal 647, Barcelona, 08028, Spain J. M. Gutiérrez Grupo de Meteorología, Instituto de Física de Cantabria (IFCA), CSIC-UC, Av. de los Castros s/n, Santander, 39005, Spain