Review of Soil Moisture Deficits, Summer 2016

‘Soils wetter than normal nearly everywhere’

Met Éireann operates a Soil Moisture Deficit (SMD) model based on the research by Schulte at al.†

This model accounts for three different drainage regimes, approximating different soil types in Ireland. These are: well drained, where the soil never saturates; moderately drained, where the soil may saturate on wet days and poorly drained, where the soil saturates on wet days and is slow to drain this excess water.

Further details of these soil drainage regimes are available at

The SMD scale goes from -10mm where the ground is considered waterlogged, to 75+mm which represents near drought conditions. The table below relates SMD values to real world physical meanings.


Reviewing this current year (June -> September inclusive) we see that this period in 2016 has had wetter soils everywhere on average, except parts of Dublin. These wetter soils are seen across all three soil types, see the figure below. Note that these average values are made up a various dry and wet periods over the four months examined.

A review of soil moisture deficits indicates that soils where wetter than normal* nearly everywhere, see bar chart. This is in line with feedback we are getting from farmers.

2016_Summer_smdInterestingly a review of the weather during this period (June to September) shows that total rainfall amounts nationally were not considered abnormal. However the ‘number of Wet Days’ (i.e. number of days when daily rainfall totals are ≥ 1 mm) were above normal. These higher number of Wet Days support the soil moisture deficits we are seeing.

† R.P.O.Schulte, J.Diamond, K.Finkele, N.M.Holden and A.J.Brereton 2005. Predicting the Soil Moisture Conditions of Irish Grasslands. Irish Journal of Agricultural Research 44: 95-110.
*  ‘Normal’ refers to the average over the period 1981-2010

Article submitted by Keith Lambkin, with thanks to Aidan Murphy and Sandra Spillane (all Met Éireann)