This semester, a HESE student submitted an academic paper to a peer-reviewed conference, the Humanitarian Technology Conference in Boston. The paper concerns the water savings potential of greenhouses, attempts to identify all of the modes in which greenhouses save water, and subsequently quantifies the water savings attributable to each mode. It’s important to understand exactly what drives greenhouse water savings so that greenhouses can be designed and farmed in a way that maximizes its water savings potential. This is particularly important in water-insecure areas of the world, where HESE delivers its affordable greenhouses.
While there is consensus that greenhouses do conserve water, the exact amount of water savings is difficult to quantify. The main source of greenhouse water savings comes from reduced evapotranspiration rates inside of the greenhouse, as previous works have concluded, but greenhouses do offer other, seldom-considered modes of water savings: namely opportunities for drip irrigation, closer crop spacing, and abbreviated crop cycles. Previous efforts at quantifying water savings have focused solely on evapotranspiration, holding parameters like crop spacing and crop cycle length constant. We argue, in the paper, that in order to obtain a more holistic water savings quantification, four distinct parameters must be considered: reduced evapotranspiration, closer crop spacing, drip irrigation, and a reduced crop cycle time.
Considering these four modes, we can actually predict the amount of water that a greenhouse, growing a specific type of vegetable, with a certain crop arrangement, in a particular setting, can potentially save as compared to an open-air farmer. The paper applies each relevant water savings mode to a GRO Greenhouse in Mozambique from a farmer growing tomatoes, and found that it can use 61% less water than an open-air farm to produce the same amount of crops. And while these four water savings modes work in conjunction to save water, the relationships between them are quite complex and should be explored in further research. For example, the reduced crop cycle length that a greenhouse induces will save water due to the fewer days spent watering the plant, and the fewer days that the plants will lose water to the atmosphere through evapotranspiration, but because of their accelerated development, the plants may require more water every day. The paper acknowledges that each mode of water savings is complex, and not easy to calculate. But what it mostly tries to do is expand the criteria for greenhouse water savings, so that the full water savings potential of a greenhouse may be unlocked.
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