As the very powerful El Niño continues to develop we need to pay attention to as many signals as possible to enable us to determine early what impacts could be experienced in the Garden Route.

The latest ECMWF soil-moisture forecast, valid up to 31 August, suggests that parts of the Western Cape are moving toward less favourable soil-moisture conditions after the below-normal rainfall experienced in July and, so far in August.

The area highlighted above in red is in the green portion of the ECMWF soil-moisture scale, which represents soil moisture between the permanent wilting point (PWP) and field capacity (CAP). Within this range, the model estimates that evapotranspiration efficiency increases with increasing soil moisture, reaching 100% at field capacity.

This means the soil still contains water, but continued rainfall declines, particularly as it gets warmer, would progressively reduce soil moisture.

This does not mean that the Western Cape is already experiencing soil-moisture stress but it is an early signal that the reduced rainfall is beginning to have an impact on soil moisture levels.

For the Garden Route, this is something we will be watching closely. Rainfall for August is currently running at approximately 14% below average, following below-normal rainfall that was recorded in July. The key question now is whether rainfall during September and October will be enough to keep soil moisture in the above ranges before the warmer and therefore greater evaporation conditions set in.

To sum up, while the rainfall numbers are important soil moisture levels will tell us when the decrease in rainfall begins to have an impact on the 1 m soil moisture levels.