Wood decay hazard in Spain using the Scheffer index: proposal for an improvement

Wood in outdoor conditions is prone to water uptake and release. The influence of wood temperature and moisture on the decay risk is substantial. Different climate indexes and mathematical models have been used to predict the decay risk, being one of the most well-known is the Scheffer index (SI). Scheffer index values (SI1) and modified Scheffer index values considering days with no rain but condensation (SI2) together with the risk of physical and dimensional degradation of wood (RDA) and the severity climate indexes (summer and winter) are calculated for 48 capitals of province in Spain. The relationships between the risk of physical degradation of the wood (RDA) and the climatic severity variables both for summer (SCSI) and winter (WCSI) are analyzed, and a model for predicting the RDA value from the SCSI and WCSI values is proposed. The analysis of the relationship between the Scheffer index (SI1) and SCSI and WCSI variables leads to the conclusion that the decay risk is fundamentally governed by summer climatic severity (SCSI) in coastal areas and by both variables (SCSI and WCSI) in inland areas, the relative insolation value being the variable with the most significant effect, both in summer and winter. The effect of condensations on the decay risk is also assessed, leading to the conclusion that the frequent presence of condensation is an aggravating factor and therefore, this meteorological variable should be considered when calculating the decay risk. A new equation for SI calculation considering the condensation effect, together with a new rating of risk, is also provided.