title: Measuring the impact of temperature changes on the wine production in the Douro Region using the short time fourier transform.
abstract: This paper investigates the cyclical behaviour of the wine production in Douro region during the period 1932-2008. In general, wine production is characterised by large fluctuations which are composed of short-term and/or long-term cycles. The aim of this paper is twofold: firstly, we decompose the wine production's variance in order to find the dominating production cycles, i.e we try to explain whether wine production follows more long-term or short-term cycles. In the next step, we try to explain those cycles using a dependent variable, namely the medium spring temperature (Tm_Sp) for the period 1967-2008. We estimated a Time-Varying Autoregressive Model, which could explain 75% of the production that is characterised by 4.8- and 2.5-year cycles. We use the Short Time Fourier Transform to decompose the link between wine production and temperature. When the temperature was incorporated, the R                         (2) increased and the Akaike criterion value was lower. Hence, Tm_Sp causes a large amount of these cycles and the wine production variation reflects this relationship. In addition to an upward trend, there is a clearly identifiable cycle around the long-term trend in production. We also show how much of the production cycle and what cycle in particular is explained by the Tm_Sp. There is a stable but not constant link between production and the Tm_Sp. In particular, the temperature is responsible for 5.2- and 2.4-year cycles which has been happening since the 1980s. The Tm_Sp can also be used as an indicator for the 4.8- and 2.5-year cycles of production. The developed model suggests that stationarity is a questionable assumption, and this means that historical distributions of wine production are going to need dynamic updating.
authors.affiliation: Department of Geociências, Ambiente e Ordenamento do território, Faculdade de Ciências, Universidade do Porto, Campus Agrário de Vairão, Rua Padre Armando Quintas, 4485-661, Vairão, Portugal. mcunha@mail.icav.up.pt
authors.forename: Mário
authors.initials: M
authors.lastname: Cunha
authors.forename: Christian
authors.initials: C
authors.lastname: Richter
mesh_terms: D000383:Agriculture / Q000706:statistics & numerical data; D019649:Food Industry / Q000706:statistics & numerical data; D005583:Fourier Analysis; D008962:Models, Theoretical; D011174:Portugal; D013696:Temperature; D014920:Wine / Q000706:statistics & numerical data*