Cooling the planet in Zimbabwe

The heat that naturally radiates from the Earth’s surface back into space is increasingly becoming trapped in our atmosphere by greenhouse gases. The solution is to either remove the greenhouse gases or to reduce the heat that is re-radiated. Just 4% more vegetation would radiate 80-90% of the heat back into space.

In the Chimanimani mountains of Zimbabwe, PWRDF partner TSURO Trust collaborates with local farmers to adapt to climate change and meet their families’ basic needs through agroecology.

Though we have always known how vital water is to our health, less well known is that water has always cooled our planet. Cooling the planet is now more important than ever because global warming is increasing the frequency, intensity and duration of climate events, spanning from higher temperatures, drought and wildfires, to storms, floods, rising sea levels and hurricanes. Such hazards damage the ecosystems on which we and other species depend.

TSURO’s first principal is to sink the raindrop where it falls. When that can’t be done by solely increasing the ground cover, other techniques can be used:

• Digging infiltration pits and building small gabions (rock walls) that allow the water to infiltrate through the soil slowly, through gravity or osmosis;
• Building tall rock gabions that slow down runoff;
• Constructing stone bunds (retaining walls) on contours, slowing down, infiltrating and spreading water through the soil.

Benefits of Planned Grazing

Communities in 14 wards have benefited over the years from amalgamating many small herds of cattle into one large community herd and practising planned grazing. The practice effectively ended child labour, so boys today now attend school instead of herding livestock. Women now have the choice to be paid as community herders, or to engage in other income generating activities instead of herding the small family herd, unpaid. It also has made it easier for women to be owners of cattle when they are managed as one large community herd.

Rotating one large herd in communal areas gives the grass sufficient time to recover and grow again after being grazed, just as vast migrations of wildebeest and other ruminants once followed the rains and were kept moving by pack-hunting predators such as lions. Herders today keep cattle bunched and moving to graze and trample grass, leaving mulch, dung and urine to stimulate the growth of new shoots of grass in the rainy season.

Keeping Carbon in the Soil

It is vital in seasonal rainfall environments of sub-Saharan Africa to minimize the oxidization of mature grass in the dry season. At this time of year, grass transforms from green to yellow, until finally grey and dead. Grass – made up of cellulose, which is carbon – is oxidized and released into the atmosphere as carbon dioxide. Worse is when grass is burned, because carbon dioxide and other greenhouse gases are released even more quickly. Far more ecological is for grass to be grazed by ruminants and deposited on the soil as dung where a host of micro and macro-organisms such as dung beetles can bury and sequester stable soil carbon (humus and glomalin) into the soil.

This allows roots to penetrate more deeply. Every gram of carbon sequestered into the soil can hold between 8 to 20 grams of water. This is because 66% of healthy soil is just air, pockets of space between soil particles that allow for raindrops to sink where they fall, and slowly release to roots when needed. The slow release allows for a longer growing season and draws more carbon dioxide into the soil. This in turn increases productivity and resilience of the grass and ultimately the health of the cattle.

Decreasing oxidation and increasing soil carbon is both the challenge and the opportunity for cattle owners and herders in Chimanimani district. To make the water cycle more effective, they will try to grow two blades of grass where before there was only one, for as long as possible after the rainy season has ended.

– Richard Librock is the External Grants Funding Manager for PWRDF.