Estimating MCC System Dryness Index using the Vineyard Water Indicator

¹ Embrapa Grape and Wine, Tropical Viticulture Experimental Station, Jales, SP, Brazil
² Embrapa Grape and Wine, Bento Gonçalves, RS, Brazil

Abstract

The Dryness Index (DI) is one of the three Geoviticulture Multicriteria Climatic Classification System (MCC System) indices and its calculation is based on a soil water balance approach. However, other climatic indices can be used for the same purpose. One of them is the Vineyard Water Indicator (VWI) that represents the ratio between the total rainfall and the vineyard water requirement during the productive period of the culture. When compared to DI, the VWI presents a simpler calculation methodology. Therefore, the aim of the present study was to establish a model to estimate DI based on VWI values. Climate data of 80 winegrowing regions in 18 countries were used. Four regression models were evaluated: linear, quadratic, logarithmic and the Mitscherlich model. Real and simulated data were compared using the confidence coefficient (c) that corresponds to the product of the correlation coefficient (r) by the exactness coefficient (d). The best fit was obtained employing the quadratic model and DI can be calculated using the following equation: DI = −363.84 VWI²+ 834.47 VWI – 257.17 (R² = 0.93), for VHI <0.905. For VHI values equal to or greater than 0.905, DI is constant and equal to 200.