The Science Gallery’s invitation for submissions was announced this week for their exhibition in October ‘Future of Water’. This theme reminded me of an innovative method of farming I witnessed in one of the most arid regions of Europe, Lanzarote. In contrast to Ireland, it is a dry island without fresh-water rivers or lakes. Drinking water for the cities and towns is obtained by desalination of sea water.
After learning this from the back of a hotel card that said “Your water might taste salty“, I didn’t expect vineyards to be on the tour schedule. I was even more surprised when I was informed that Lanzarote has an annual rainfall of 150mm in contrast to 980mm in France’s wine producing area of Bordeaux. To bring this home, Ireland annual rainfall is 5-8 times greater at 750-1250mm. Yet another disadvantage is Lanzarote’s hot climate resulting in huge volumes of water being lost from the soil due to evaporation and transpiration (evapotranspiration).
To understand the local farming method, a visit to Timanfaya National Park was necessary to see the Montañas del Fuego (Fire Mountains). These comprise of over 100 volcanoes which erupted between 1730 and 1736. This massive series of eruptions covered much of Lanzarote in volcanic rock fragments, tephra. At 13 meters beneath the surface, the ground temperature at Timanfaya National Park can reach up to 600 degrees which was demonstrated by the ability to create a geyser by pouring water into a pipe.
After this devastating event, most people would pack up and move on to more hospitable lands but instead the locals adapted to the new geology of the island. Not only did they have to adapt to sparse rainwater and evapotranspiration but now their land was covered in volcanic rock. They devised a system of farming known locally as enarenado (covered with sand) which allowed growth of crops without irrigation.
Upon reaching the vineyards it became obvious something different was happening as each vine was in a black hollow surrounded by a wall. The colour was from the basaltic tephra (volcanic rock fragments) which are used as mulch to cover the soil. The low water retention capacity and high porosity of the tephra mulch means that the soil it is covering retains up to eight times more water even during the driest months. This occurs as it increases the amount of water filtering into the soil and reduces water leaving through evaporation.
A disadvantage to this system is that it is very labour intensive as everything has to be done by hand including replacing the mulch as it deteriorates over time. However, this innovative method of water conservation allows locals to produce yields on crops including onions, potatoes and grapes even in extremely dry years such as 2000 where there was only 69mm rainfall in the year. That is slightly more than twice the annual rainfall in parts of the Sahara desert (<25mm)!
So back to the future… of water! Temperature changes as a result of greenhouse gases such as carbon dioxide and methane will change rainfall patterns across the world. Projections of rainfall changes predict that rainfall in some areas will decrease in the coming decades (see video from the UK Met Office above). Mulch similar to that used in Lanzarote could be an agricultural solution for future arid areas. Perhaps in the future, systems will be invented to allow even better water conservation and technologies will be developed for a less labour intensive process. Saharan wines could be on our supermarket shelves!