In Reunion Island and other areas where mechanised sugar cane production is practised under wet tropical conditions, soil trafficability is decisive at the time of the annual harvest and post harvest works which involve the use of heavy machines causing compaction problems. Problems relating to the planning of harvest operations are predominant. Operators are faced with two types of question : i) what is the risk involved, and what are the probable results of an operation undertaken at a given period ? How and when can problems of compaction be remedied if they arise (decompaction after harvest) ?; and complementary to this, for planning purpose, ii) which is the period, or which are the days best suited for the operation in a given area ? First, trafficability is examined from a compaction susceptibility viewpoint. A critical threshold for moisture content is evidence by way of the modified Proctor test. Then, a model for climatic evolution of moisture content on the upper layer of the soil is developed. It is calibrated and takes into account the specific characteristics of cane growing and certain decision criteria used by operators. From the moisture content threshold determined, the model can coonstitute a decision system, i) at particular moment using recent climatic data, ii) prospectively on virtual scenario and, iii) for yearly planning purpose, from frequencial analysis of occurence of trafficable days