Figure 2: Normalized growing degree days for Blenheim: days above (+) or below (-) the long-term average (1990-2016) for the period 1 September to 30 April
far the lowest January total on record for Blenheim for the 33 period 1986 to 2018. In marked contrast January 2017 was very windy with average daily wind-run of 336.3 km; (average wind speed 14.0 km/hr); i.e. January 2018 recorded only 57% of the wind-run recorded in January 2017.
potential evapotranspiration = -55.2 mm potential water deficit This is a low total for January in comparison to the LTA of -99.7 mm. In contrast the potential water deficit in January 2017 was -154.3 mm, the highest on record 1997-2018.
Potential evapotranspiration
Average shallow soil moisture (0 to 35 cm) at the Grovetown Park weather station for January 2018 was 28.1%. This is the highest January average for the 16 years 2003 to 2018 (period of record). However, on 2 January the topsoil moisture was only 15.5%, slightly above its driest point. Rainfall from the 4th to
Total potential evapotranspiration for January 2018 was 135.6 mm, 95% on the LTA. Despite the warm temperatures, the evapotranspiration was kept fairly low due to the lack of wind, lower radiation and higher relative humidity. In contrast January 2017 recorded 181.3 mm evapotranspiration, by far the highest January total on record for the 22 years 1997-2018.
Shallow soil moisture (topsoil)
the 13th January boosted soil moisture from 15.5 to 35.8%. The result of this rapid increase in soil moisture was to bring unirrigated lawns and pasture back into life with a flush of midsummer growth. A further 10 mm rain on 17 January gave topsoil moisture a top up, helping to prolong the grass growth. Rob Agnew Plant & Food Research / Marlborough Research Centre
Potential water deficit This is the difference between monthly rainfall and potential evapotranspiration. 80.4 mm rainfall – 135.6 mm
Winepress February 2018 / 9