Water status modelling: impact of local rainfall variability in Burgundy (France)

Water status is a key factor in vine development and berry ripening. Water status is strongly affected by environmental parameters such as soil and climate. Whereas at local scale the soil variability is frequently accounted for, little scientific reports are available concerning the impact of local rainfall variability on grapevine water status. In order to accurately register the space and time variations of rainfall at local scale, a dense rain-gauges network has been installed in Burgundy. It is composed of 45 rain-gauges over a 28 km² area. Rainfall data collected by each rain-gauge in 2014 and 2015 was used as input variables in the grapevine water balance model proposed by Lebon et al (2003). All other climate variables, vineyard and soil parameters were kept strictly identical for each simulation in order to capture the consequences of the sole spatial variability of rainfall on vineyard water status.

As rainfall dynamics impact on the vineyard depends on the soil water content, water balance was modeled considering successively soils with low (50 mm) and medium (150 mm) soil water holding capacities, representative of the soils of the area. The daily fraction of transpirable soil water, averaged on the grape ripening period, was used as an output variable to assess the potential consequences of soil water status on grape characteristics.

During the 2014 (2015) vintage, the mean FTSW from veraison to harvest varied from 0.22 to 0.41 (0.09 to 0.25) for soils with low water capacity with an average difference of 0.04 (0.03). Ranges of 0.31 to 0.76 (0.09 to 0.16) with average differences of 0.09 (0.02) were observed for soils with higher water capacity in 2014 (2015). Therefore, it seems that the spatial variability of rainfall at local scale could significantly affect the vineyard water balance, depending on the vintage and the soil water capacity.
The contribution of local rainfall variability to vineyard water balance in comparison to other factors also impacting the vineyard water status is discussed.