Earthshots: Satellite Images of Environmental Change

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» Lake Naivasha, Kenya
 

How do those in northern winter climates get roses to their loved ones in February for Valentine’s Day? The answer is to import them from warmer climates.

Kenya offers the perfect climate for flowers year-round. Its floriculture industry covers land near a shallow lake near the equator. Lake Naivasha is one of the few freshwater lakes in East Africa. Its depth varies from 2 to 8 meters, and the surface area as shown in the 2019 Landsat image is about 150 square km.

Direct rainfall on the lake and three rivers feed freshwater to the lake. The Gilgil and Malewa are perennial rivers, and Karati is a seasonal river. The Malewa contributes up to 90% of the water to the lake. The lake has no surface outlet—it is referred to as an endorheic lake. In most endorheic lakes, salts are left behind when the lake water evaporates. That is, the salts are not washed out through an outlet to another outgoing river. Lake Naivasha, however, maintains its freshwater status because the lake water seeps into the ground, taking the salts with it.

The wetland areas around the Lake Naivasha support not only the large flower industry but also fishing, tourism, and geothermal power. Hundreds of millions of dollars’ worth of cut flowers are exported from Kenya to Europe and other countries. As of 2018, Kenya has 38% of the European Union’s market for cut flowers.

The region offers steady sunlight and days that vary very little in length. Lake Naivasha is not far from Nairobi, Kenya’s capital and largest city, about 90 km away. So transport is relatively easy. The Nairobi airport has a terminal dedicated to transporting flowers and vegetables.

Still, the industry has had challenges. In recent years, workers have been laid off because of lower demand and higher costs. The increase in agriculture has put pressure on the water resources of the area, affecting the water quality of the lake.

Map of the featured area.

The cut flower industry can be seen in Landsat images near the lake in both outdoor fields and in glass greenhouses. The greenhouses are silvery in these views. The fields are a mix of green, tan, and purple. Tan and pink are fallow fields, and the green fields have growing plants. These fields and greenhouses have expanded over the time frame covered by these images.

The flowers grown in the region include roses, carnations, statice, alstromeria, lilies, and hypericum.

Since 1986, the nature of agriculture around Lake Naivasha has changed from mostly ranching to floriculture. The flower industry especially has led to increased population in Naivasha and the surrounding area. From 1969 to 2009, the population of the Naivasha Division increased more than 750%.

Population of the Naivasha Division
YearPopulation
2009376,243
1999158,679
1989105,458
197995,339
196943,867

 

The flower farms use a lot of water from the lake and send nutrients and chemicals back to the lake. In addition, the increased population is placing more pressure on the freshwater resources in the region. As a result, the chemistry of the lake is changing. More blue-green algae and tiny crustaceans are appearing in the lake, which are food for flamingoes. The pink birds usually flock to lakes salty enough to find this food, so it was unusual to see them in abundance at Lake Naivasha.

Floriculture began around Lake Naivasha in the early 1980s. During the 1990s and early 2000s, the amount of land dedicated to floriculture rapidly increased, changing from grassland and shrubland to flower farming. The increased water use led to a drop in the water level of the lake and an increase in farm runoff laden with agro-chemicals.

The Sentinel-2 satellites from the European Space Agency (ESA) use infrared imaging to highlight certain information about the land surface. In the near-infrared wavelength of light, actively growing vegetation appears red in these images that show the lake more closely at a resolution of 10 m.

The cropland appears in bright red around the lake, and the greenhouses are the light blocky shapes. However, bright red swirls also appear on the surface of the lake, and the extent and location change in each image. Sentinel’s near-infrared proves that it’s vegetation and that it’s alive.

The nuisance plant is water hyacinth, a fast-spreading, free-floating plant that forms moving, impenetrable mats. It hinders boating and fishing and interferes with the ecology of the lake.

European settlement in the early 1900s likely brought hyacinth to Lake Naivasha. Around 1920, hyacinth was tossed into the lake to beautify it. Low nutrients restricted it to the shallow northern shores for decades. It spread to other parts of the lake in the 1980s. The flower farms increased at this time, using so much water that the lake level dropped, exposing hyacinth seeds. As the lake became over-enriched with farm runoff, the hyacinth thrived.

In the Landsat images in the other sections, the near-infrared wavelength is used to make vegetation appear green. The extent and location of the hyacinth on the lake’s surface changes over the years in those images, visible as the bright green shapes on the lake.

The hyacinth was at first limited to protected bays and estuaries. The western part of the lake has been most affected recently, but these images do show it spreading over various parts of the lake. Scientists will continue to use Sentinel, Landsat, and other remote sensing instruments to track the changes caused by the blooming cut flower industry.

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