This special issue of Global and Planetary Change is the fourth related to the World Climate Research Programme's Project for the Intercomparison of Land-surface Parameterization Schemes (PILPS). The first volume published in 1996 was a collection of the papers arising from the first intensive workshop of this project. The second special issue in 1998 represented a world-first intercomparison of the land-surface simulations by a wide range of AGCMs. The third collection, published in 2003, was another magnificent statement brought together following an extraordinarily successful experiment and workshop analysing the simulations of the Thorne-Kalix Rivers. This volume marks a new aspect of PILPS and also follows in these footsteps, being a collection of papers stemming from an extraordinarily successful working meeting in April 2005.