Drought and Low Temperatures = Double Whammy

This blog continues my last discussion of what is now recognised as a drought ("A period (long) of dry weather that is harmful to crops").  In North Canterbury it is the worst since 1997-98.  Two months into autumn and a drought’s worst enemy is omnipresent – cold soil temperatures on top of large soil moisture deficit.  Soil moisture deficit is still significant (70mm over the depth 0-200cm in the example shown) despite rainfall of 35mm.  What little is now growing at this site has resulted in reducing the deficit by about 25mm from the wilting point soil moisture content in early March.  

Time plot of soil moisture (mm) near Christchurch

The rainfall events are from the southerly quarter and are associated with cold temperatures.  Soil temperatures fell to below 10°C at 9am for consecutive days – the first time since October 2014.  Low soil temperatures and continued soil moisture deficit (especially in North Canterbury) is bad news for unirrigated farmers.  The soil moisture deficit is bad enough, but coupled with low soil temperatures makes for a double whammy.

Blog post by Dr Anthony Davoren from HydroServices Ltd