A year in Lambani

During our meeting with farmers in Lambani, we compiled a graph sketching the last season with respect to rains, crops, droughts, etc. Information was gathered in different forms and will be compiled and presented later.

A year in Mokwakwaila

For us to better understand a typical season at one of the research sites, we had the pleasure to sit down and discuss with some of the local farmers. Sketching down the information on a piece of paper resulted in this graph.

The 2013-2014 season was in short a good year (for the home-garden farmers), water supplies were good, etc. We will further compile the information we got from the other farmers that kindly received us on the 19th of May, 2014.

Example model analysis of soil moisture data

In the figure below, I have taken the data from the Mokwakwaila office station. We are looking at the measured data from the most shallow sensor. In addition to this, I have created a model that takes the precipitation into account, as well as evaporation and run-off. The numbers are displayed in per cent.

The model looks something like

topModel(m) = topModel(m-1) + scaleRain*(rainfall(m) + rainfall(m-1)) - topModel(m-1)*topModel(m-1)*(evaporation + dillution)*(timeVector(m)-timeVector(m-1));

The current, modelled value of soil moisture is equal to the previous one plus rain times a scaling factor. In addition to this, moisture will disappear through air and ground, this is a time-dependent parameter and it will also depend on the soil moisture itself. I have assumed a square model. The more moist it is, the more will evaporate.

Evaporation, etc., is also a function of air and soil temperature, not included here, that would further refine the model. Evaporation and dillution, is approximately 2% per hour.

Today's sensor data

Just since I prepared the files for some eye inspection, I thought we could add them here too.

Below you find the data underneath each other and in the same scale. The data is recorded at the Mokwakwaila office and at the Morwatshela high school. The plots are spanning from June 2013 until today. Notice that one of the sensors were installed some three months later than the other. This explains the long straight line from June to November 2013.

With the two graphs in front of us, we can at least see some correlation between the values with the naked eye.

The office station also has a rain gauge and we can see that there was quite heavy rain at the end of January. This also forms a peak in the soil moisture at the school. If we look at the accumulated rain over seven day periods over the year, Mokwakwaila received 75 mm during end of January. Interestingly, there was an earlier rain fall, flood, on Jan 6, where 61 mm was registered during 6 hours.

Just for the interested, a quick comparison of the different soil moisture values are given in the figure bellow. The curves can be identified from above (green: deep@school, yellow: shallow@office, red: deep@school, blue@office).