The Impacts of Agriculture on the Environment: Land and Water Resources

The relationships between agriculture and climate change are complex which involves the interaction between land use, food and the environment. So I would like start by introducing some of the major effects of agriculture onto the environment, including changes in landscape, depletion of water sources and intensive GHG emission into the atmosphere. Today, I will be focusing on the first two. 

Land Degradation

First, I would like to take you on a little journey to our planet from space.

Fig 1. June 19, 1975, Landsat 2 (path/row 249/67) — Rondônia, Brazil (Source: USGS)Deforested land and urban areas appear lavender, healthy vegetation appear green. 

Fig 2. July 16, 1986, Landsat 5 (path/row 232/67) — Rondônia, Brazil (Source: USGS)

Fig 3. Aug. 10, 2001, Landsat 5 (path/row 232/67) — Rondônia, Brazil (Source: USGS)

  Fig 4. July 5, 2011, Landsat 5 (path/row 232/67) — Rondônia, Brazil (Source: USGS)

Above is a series of Landsat images, showing part of the Amazon basin, in a state called Rondonia located at West of the Brazilian Amazon. In the first image, one thing we would notice is the thin white lines on the right-hand side, they are roads built in the 70s. If we come back to the same place in 1986, what we can immediately see are the expansions of roads and urban areas in a fish-bone pattern. Then this pattern of clearing forest continued through 2001 into 2011, causing the whole place to be dramatically changed, with roads and human facilities occupying the original rainforest like spider webs. Rondonia was once home to 208,000 km^2 of forest, now it has become one of the most deforested parts of Amazon, with an estimate of 67,764 km^2 of rainforest have been cleared until 2003. 

The deforested lands are mostly used for cattle ranching. The cows here would be used to produce beef and exported around the world. Currently, the Amazon is home to approximately 200 million cattle, with most of the beef destined for urban markets. And as the largest exporter to the world, the cattle industry here supplies about 1/4 of leather and other cattle products of the global market. As a consequence, cattle ranching is the leading cause of deforestation in the Amazon rainforest. It attributes close to 70% of deforestation in Brazil. 

Fig.5 Cause of Deforestation in the Amazon based on the median figures for estimate ranges 
(Source: MONGABAY)

Another major driver of deforestation in the Amazon basin is soybean cultivation. 
Soybean seeds contain high protein content, so 80% of Amazon soy is being shipped to Europe and China as livestock feed, especially after the mad cow disease during the 90s. Since animal protein can transmit disease, people feed livestock vegetable protein instead. Today, Brazil has about 24-25,000 km^2 devoted to soy cultivation and is the second large producer of soybean in the world.  

The Amazon is just one of the examples of landscape after landscape that have been cleared and altered for growing food and other crops. At present, according to the World Bank, about 37% of land surface is devoted to agriculture, this is about 60 times larger than all the area we live in. Of course, we have been using the best land, what is left are lands like the Sahara Desert, Siberia or the middle of the rainforest. 

Freshwater Decline

Other than using an enormous amount of land to feed us, we are also using plenty of water. Currently, we have used about 50% of Earth's sustainable fresh water, with about 70% of it go towards irrigation use for agriculture. For a more intuitive illustration, let's look at another group of Landsat images. 

Fig 6. Sep 1, 2, 3, 22, 1977, Landsat 2 (path/row 172–175/27–30) — Aral Sea (Source: USGS)

Fig 7. Sep. 18, 27; Oct. 27, 1998; Aug. 20, 1999, Landsat 5 (path/row 160–162/27–30) — Aral Sea (Source: USGS)

 Fig 8. July, 24; Aug. 2, 11, 2010, Landsat 5 (path/row 160–162/27–30) — Aral Sea (Source: USGS)

Fig. 9 Aug. 20, 29; Sep. 7, 2014, Landsat 8 (path/row 160–162/27–30) — Aral Sea (Source: USGS)

The above images show the drying of the Aral Sea, which is located in the former Soviet Union in between Kazakhstan and Uzbekistan. The Aral Sea was once the world's 4th largest body of inland water, covering about 68,000 km^2. Now it only holds 10% of its original volume of water. The Aral Sea used to have two rivers feeding this basin with snow-melt from large permanent snowfields and glaciers in mountains from the far east. As the precipitation rate over the area is very low, the water level largely depends on the inflow of these two rivers. However, in the 1950s, the Soviet decided to divert this water to irrigate cotton in the desert. The turn-off of water supply caused the Aral Sea to dry out at a high rate. 

The effects of this dramatic change are far-reaching: geographically, environmentally and economically. Fishers and the community that depended on them collapsed. Local freshwater species died off when the water turned increasingly salty. 19 of the unique fish species found only the Aral Sea is now wiped out. The remaining water wad also polluted due to fertilizers, pesticides and metals. These toxic waste collected at the lake bed are becoming air-borne as the sea further dries out, causing public health hazards. The weather pattern has also changed. Without the moderating effect of the water body, winters are colder and summers hotter, which cause a shorter growing season.