This model demonstrates the complexities of the effects of reducing postharvest losses. There are weight losses at each link in the postharvest chain. The model includes eight separate links. Losses can occur at any, or all, of these links. Each link represents a set of activities with associated postharvest technologies.
Changes in the types of technologies and/or the ways they are applied will either increase or reduce the weight losses at that particular link. The change in losses at one link will naturally affect the absolute weight losses at other links even if the technologies and the way they are applied are unchanged at the other links.
An initial weight loss is ascribed to each link: these values are illustrative examples only and are taken from loss profile figures used in the African Postharvest Losses Information System (APHLIS).
The parameters of a loss reduction intervention are displayed graphically for each link in the chain. Click on one of the links in the left hand panel and a graph is revealed. Three parameters are visible, each controlled by a ‘slider’.
The first, above the graph is the ‘Investment’ planned to reduce the loss at that link (investment here can be taken as resources applied either as money, time, effort etc). Greater investment will not automatically reduce losses but is dependent on the other two parameters.
These are the ‘Adoption rate’, along the X-axis, and ‘Efficiency’ along the Y-axis. The ‘Adoption rate’ is the changing rate of return on investment in loss reduction that comes from a greater degree of adoption of an existing technology or switch from a less effective to a more effective technology. This slider has two buttons which can be used to alter the shape of the rate of return making it either stepwise (maximum 2 steps) or simply linear if each button is at the opposite end of the slider. When the rate’s shape has 2 steps, under the first threshold, the investment is too low and there is no adoption, in the middle section, an increase in investment results in an increase in adoption, when above the second threshold, we have reached a situation where there is a much more rapid return on investment.
The ‘Efficiency’ slider defines the limitations of the technology to reduce losses. It can be set at 100, meaning a complete reduction of losses at this link or at say only ‘50’ meaning that however well applied the technology can only reduce losses by 50%.
The header on each postharvest link provides a losses summary even if the graph is hidden: the investment level is displayed in the grey box, a pink bar show the original % weight loss as per the APHLIS profile and a red bar shows the % weight loss remaining after loss reduction is achieved by the intervention.
For an example of loss reduction using this model see this link.
The outputs of the model are displayed in the right hand panel. The top set of bars, in green, show the amount of grain remaining after losses are deducted. This starts with the mature crop in the field before any postharvest losses, i.e. is 100%. As losses are reduced the green bars will increase in size, except of course for the top one, the mature crop.
Immediately below the green bars is a single red bar that presents the cumulative loss taking account of all links in the chain. Overlying the red bar there will be a pink bar showing the extent of loss reduction, provided some reduction has been achieved.
Below this, there is a set of red bars that show the loss at each link in the chain, again with a pink bar overlying each if a reduction in loss has been achieved. The red bars are the inverses of the green bars.