Case Study Analysis - Mozambique Images and Data 1973, 1985, 1992, 1994, 1995
(downloaded 12Feb2008 from http://earthshots.usgs.gov/Mozambique/Mozambique)
These images center on the town of Mutarara, Mozambique, in southeastern Africa.
Look at the false-color satellite images from 1973, 1985, 1992, 1994 and 1995. What can you tell from them? It is hard to read the subtle changes, especially at this scale. But in these years Mozambique was embroiled in civil war, and expert interpretation of these images at full resolution reveals the war's effects.
|
|
|
||
|
Preindependence: 15 Aug 1973, L1 MSS 4 2 1 |
Postindependence: 11 May 1985, L4 MSS 4 2 1 |
||
|
|
|
||
|
Above - Returnees: 28 May 1994, L5 TM 4 3 2
Left - Most recent: 20 Apr 1995, SPOT3 3 2 1 |
Mozambique: three decades of war
Mozambique was a colony of Portugal until 1975, when an 11-year war of independence ended with the establishment of an independent, Marxist government. But a 17-year civil war started soon after independence, with an internal military uprising that was supported by some foreign governments.
The civil war affected Mozambicans severely, especially in rural areas. Hundreds of thousands of people were killed. Over a million people fled the country, especially to Malawi, and more than a million others were displaced within Mozambique.1 Many rural people migrated to the cities, especially along the coast where the government maintained control. The country went into severe economic depression.2 Agriculture was disrupted, so the country could not feed itself. By the late 1980s Mozambique had one of the lowest per-capita caloric intakes in the world.3
Mozambicans also suffered though an El Niño-related drought during the war's last year, 1991-1992. This regional drought was especially hard on Mozambique.4 People were already malnourished, and had few resources to fall back on. Even when relief food eventually flowed in from other countries, Mozambique's war-ravaged transportation system prevented efficient distribution of the food, and internal politics interfered with relief work. Mozambique was said to have the highest "misery index" in the world, with 5 million of 16 million inhabitants in need of food and medicine.5
April 1995, bridge at the Sangadza River
The streambed of this river is dry sand in this photograph. On the left, a group of women and children is collected on the remnants of a bridge, apparently doing laundry (they have a large yellow bucket). The hole in the foreground, surrounded by footprints, is a hand-dug open well. The white vehicle with the blue flag is carrying workers from the United Nations High Commissioner for Refugees, who are assessing the reintegration of returning refugees.
Remote sensing: early warning
The U.S. Agency for International Development (USAID) runs the Famine Early Warning System (FEWS), which monitors drought-prone countries in Sub-Saharan Africa, to quickly detect droughts and crop failures which could lead to mass hunger and starvation. FEWS was established in reaction to the 1984 Ethiopian famine, which most of the world learned about only when thousands of people were already starving.
FEWS personnel monitor rainfall, crops, grazing and markets on the ground, but they also use satellite data to monitor large areas of cropland, by using maps of NDVI (Normalized-Difference Vegetation Index). Healthy plants have the special quality of absorbing visible sunlight to photosynthesize, but reflecting infrared sunlight to keep cool. Therefore satellite data over a vegetated area should have a large difference between the infrared and visible bands, represented by a high NDVI value (here on a scale of 0 to 1). If the satellite flies over croplands during growing season and "sees" a low level of NDVI, then FEWS knows there may be a problem.
21-30 June 1992, NOAA 11 AVHRR bands 2 1 1
This is what happened in Mozambique during 1991-1992. By January 1992, governments and organizations in southern Africa described a looming food shortage so large that many foreign governments and organizations had to send their own people to check before they could believe it. This led to delays, and full-scale relief efforts did not start until June or July. The "notable exception", according to one African report, "was the Government of the USA which was able to verify the anticipated severity of the drought through its USAID supported Famine Early Warning System... [and] which took immediate action". U.S. grain shipments were among the first to reach African ports.6
Remote sensing: relief support
The U.S. Geological Survey (USGS) Center for Earth Resources Observation and Science (EROS) has supported FEWS since 1987, handling its satellite images and other electronic data. These data are available through the Africa Data Dissemination Service.
For the 1991-1992 crisis, EROS scientists made a map showing where crops had previously been grown, to help assess the situation and target assistance. This Cropland Use Intensity (CUI) map was created by an experienced satellite-image interpreter drawing on large printed Landsat scenes, outlining areas with similar levels of cropping. A high-CUI zone is 70-100% agricultural fields. The lowest CUI category has 0-5% cropland. The photointerpreter used clues such as color, texture, and context to estimate CUI. The prints were then converted into the electronic map you see here.
1986-1988 estimated Cropland Use Intensity
Remote sensing: historical documentation
In 1995, three years after war ended, USAID asked the USGS to try documenting the migration of rural Mozambicans during the civil war using Landsat and other satellite data. These satellites cannot see people, but they can see farms; for this reason, CUI was used again. In areas of subsistence agriculture, CUI approximates population density. CUI can also be used to spatially disaggregate agricultural statistics-- for example, if Sofala Province reports a 50% rise in planted grains, CUI can tell us where in the province the grains were planted.
Using the process outlined above, a small part of Mozambique was mapped for five different times, representing various stages in the civil war. The CUI maps showed that 22% of the land was cropped before independence (1973). This dropped to 5% by the end of the civil war (1992), and rebounded to 17% by 1995. These maps also included administrative boundaries, towns, rivers and roads. The maps distinguished mined roads, unmined roads, and demined roads (from December 1994 data; all roads were assumed to be unmined in 1973 and 1985, and any roads mined or demined in 1994 were assumed to have been mined in 1992). This is an example of how satellite data and other digitized data can complement each other when juxtaposed.
(Read a report on the making and interpretation of these maps – follows after the Footnotes).
Footnotes
Thanks to SPOT Image Corporation for use of the 20 April 1995 scene.
1. Mike Sill, 1992, A geography of war: Geographical Magazine, November 1992, p. 45-50.
Other references
Tom Crawford, Ron Lietzow and Jim Verdin, 1996, 1995 Pilot Study; Cropland Use Intensity Interpreted from Satellite Imagery of the Mutarara/Sena Area, Mozambique: Hughes STX Corp. Center for Global Change newsletter, Vol. 3, December 1996.
Kevin J. Dalsted and Fred C. Westin, 1996, An overview and evaluation of cropland use intensity in Africa: Sioux Falls, S.D., USGS EROS, Pecora 13 conference proceedings, in press.
Harold D. Nelson, ed., 1984, Mozambique; a country study: Washington, D.C., Foreign Area Studies, American University.
Satellite images
LM1179072007322790 (Landsat 1 MSS, 15 August 1973)
XF8F41030007061 (Landsat 4 MSS, 11 May 1985, held by the South African station of the Landsat Ground Station Operations Working Group (LGSOWG))
LT4167072009205510 (Landsat 4 TM, 24 February 1992)
YFYF16772940528 (Landsat 5 TM, 28 May 1994, held by the South African station of the Landsat Ground Station Operations Working Group (LGSOWG))
31433859504200752001X (SPOT 3 HRV multispectral, 20 April 1995, courtesy of SPOT Image Corporation)
Maps
Army Map Service, U.S. Corps of Engineers, 1955 [compiled 1955 from 1939-1954 sources], Salisbury: International Map of the World SE-36, edition 2, series 1301, scale 1:1,000,000.
Mutarara/Sena CUI maps: U.S. Geological Survey, 1995, Mozambique Cropland Use Intensity [1973-1995]: Sioux Falls, S.D., EROS.
Four-country CUI map: U.S. Geological Survey, 1992, Southern Africa Region Cropland Use Intensity (CUI) [1986-1988]: Sioux Falls, S.D., EROS. Available from the Africa Data Dissemination Service (ADDS).
Four-country NDVI averages: U.S. Geological Survey, 1997, Normalized Difference Vegetation Index (NDVI), Dekadal Average for Africa, ed. 1: Sioux Falls, S.D., EROS. Available from the Africa Data Dissemination Service (ADDS).
1995 Pilot Study: Cropland Use Intensity Interpreted from Satellite Imagery of the Mutarara/Sena Area, Mozambique
Tom
Crawford,
Hughes STX Corporation, U.S. Geological Survey (USGS) Center for Earth Resources
Observation and Science (EROS)
Ron Lietzow, Hughes STX Corporation, U.S. Geological Survey (USGS) Center
for Earth Resources Observation and Science (EROS)
Jim Verdin, U.S. Geological Survey (USGS) Center for Earth Resources
Observation and Science (EROS)
[This article is reprinted from the HSTX Center for Global Change newsletter, Vol. 3, December 1996, courtesy of the authors and Hughes STX Corporation. This file was created by scanning and optical character recognition; some minor edits were made for HTML compatibility.]
Background
In 1975, after 11 years of war, Mozambique became independent of Portugal under a single-party, Marxist-Leninist government. The new government began to collectivize large farms that had been owned mainly by Portuguese farmers. Following independence, however, economic conditions deteriorated, and in 1979 an armed, anti-communist rebellion began. Guerilla warfare engulfed Mozambique and continued until a general peace accord was signed by the government (Frente para a Libertacdo de Mocambique, FRELIMO) and the Resistenca Nacional de Mocambique (RENAMO) in October 1992. Following the signing of the Rome Peace Accord, and anticipating an end to a devastating regionwide drought, the first wave of Mozambican refugees returned from Malawi between October 1992 and January 1993. Some of the returnees planted, cultivated, and harvested crops during this first postwar agricultural season. In 1993, the U.S. Agency for International Development (USAID) began a program to rehabilitate transportation infrastructure through land mine removal and road and bridge repair. In addition, USAID continued a program to provide necessary inputs to agriculture, such as seeds and tools, as well as food and other urgent assistance needed by returnees and others affected by war and drought. Between 1992 and 1995, peace was restored, more than 1.8 million refugees and nearly 4 million internally displaced persons returned to their homes and farms, peaceful multiparty elections were held, and economic activity-- particularly agriculture related-- increased.
In 1995, USAID contacted the U.S. Geological Survey (USGS) to do a pilot study to evaluate the usefulness of interpreting satellite imagery to document the return of Mozambicans to the countryside around the towns of Mutarara and Sena near the Zambezi River. Cropland Use Intensity (CUI) can be interpreted from satellite imagery as an estimate of the percentage of land area used for cropping (Table 1). It has been used successfully in Africa for a number of applications. Estimates of CUI have been employed as a surrogate for rural population density by USAID's Famine Early Warning System (FEWS) project. In Mozambique, the FAO in 1985 prepared a Land Use Inventory of Mozambique, including CUI categories, that showed high correlations between CUI and population density. The USGS has used CUI in the Sahel to support interpretation of Normalized Difference Vegetation Index (NDVI) images derived from Advanced Very High Resolution Radiometry (AVHRR) satellite imagery and to spatially disaggregate agricultural statistics.
Table 1: Characteristics of Cropland Use Intensity (CUI)
-----------------------------------------------------------------------------
How is CUI expressed? Class Interval Middle value
1 70-100% 80%
2 50- 70% 60%
3 30- 50% 40%
4 5- 30% 20%
5 0- 5% 1%
Estimated Area Cultivated: Product of polygon area and middle value.
Ideal Date of Satellite Image: Early dry season, after harvest and before burning.
Key Indicator: Contrast between cut fields and surrounding vegetation.
Modifiers: Alluvial, upland, and surface water.
Scales: 1:100,000 (1 cm = 1000 m, or 1 inch = 1.6 miles)
1: 50,000 (1 cm = 500 m, or 1 inch = 0.8 miles)
Selection of Satellite Scenes
The area of the pilot study includes the towns of Mutarara and Sena in central Mozambique and portions of the Zambezi and Chire Rivers. It is roughly centered on the town of Sena (across the Zambezi River from the town of Mutarara) and encompasses agricultural areas of interest to the east of Sena, between the Zambezi and Chire Rivers and along the south side of the Zambezi River along the road to Caia.
Figure
1
A sequence of several steps was followed in carrying out the pilot study. First, cloud-free images were selected from archived satellite images. The ideal time of year for each of the images is early in the dry season, after harvest and before burning. In Mozambique, this period falls in April and May, when there is good contrast between the cut fields and still-standing adjacent, noncrop vegetation. Five time periods were targeted, corresponding to contrasting biophysical and socioeconomic conditions in the study area (Table 2).
Table 2: Target time periods
----------------------------------------------------------------------------
April/May 1975 Cultivation patterns before independence on July 25, 1975.
April/May 1985 Following departure of colonial companies, creation of state-owned farms, "villagization" program, and other postindependence agriculture policies; but before widespread war-related destruction and depopulation, which began in 1986.
April/May 1992 Near-maximal population displacements due to civil war and drought, preceding the October 1992 Peace Accord.
April/May 1994 Postwar land use patterns affected by cessation of hostilities, influx of refugees, greater rainfall, and removal of land mines from roads. Second harvest since Peace Accord and USAID rehabilitation activities.
April/May 1995 Most recent harvest following end of major return migrations of refugees and displaced persons. USAID-sponsored land mine removal and rehabilitation support continue.
Catalogs of archived, satellite imagery acquired by Multispectral Scanner (MSS) and Thematic Mapper (TM) sensors on Landsat satellites, and by Multispectral (SX) sensors on the Systeme Probatoire d'Observation de la Terre (SPOT) satellites, were searched for cloud-free scenes. Images that were cloud free or nearly cloud free were located for 1973, 1985, 1992, 1994, and 1995 for the area of interest (see Figure 1) for the dates shown in Table 3. It was not possible to obtain a cloud-free scene for the April/May period for 1973 and 1992.
Table 3:
Available Satellite Imagery
Date Sensor Res. Extent, km Conditions
--------------------------------------------------------------
15 Aug 1973 MSS 80 m 180 x 180 Preindependence
11 May 1985 MSS 80 m 180 x 180 Postindependence
24 Feb 1992 TM 30 m 180 X 180 Peak Displacement
28 May 1994 TM 30 m 180 X 180 Returnees
20 Apr 1995 Xs 20 m 60 x 60 Most Recent
MSS = Landsat Multispectral Scanner
TM = Landsat Thematic Mapper
XS = SPOT Multispectral
The digital data for these five scenes were geocorrected and then printed at
scales of 1:100,000 for MSS and TM, and 1:50,000 for SPOT on 40" x 40" (102 cm x
102 cm) paper. False color (red) was used to indicate response in near infrared
wavelengths, which is especially useful for discriminating different vegetative
cover types.
Cropland Use Intensity (CUI) Estimation
An experienced satellite image interpreter delineated zones of CUI with ink on mylar overlays for the satellite image prints. Cues including color, texture, and context were used to define the zones of relatively homogeneous level of cultivation. The landscape was also divided into major regions-- alluvial, upland, and surface water. The mylar manuscripts were then digitized to create the information "layers" used in a geographic information system.
Geographic Information System (GIS) Analysis
The analyst and GIS Data Management Specialist created data layers to indicate the location of towns, roads, and hydrographic features in the area of interest. An information layer for the roadway network was used to provide context to the CUI findings, and information of December 1994 was used to indicate road rehabilitation activities that have taken place. Techniques of GIS overlay analysis were employed to quantify the differences in CUI over the five dates chosen for the pilot study.
Figure
2
Results: Study Area CUI -- Four Maps
The study area includes 1,078,031 hectares, or 10,780 sq km (Figure 2). The Mozambique Cropland Use Intensity map of August 15, 1973, indicates 30-50 percent CUI in most of the area in an approximately triangular zone defined by Sena, Tembe-Tembe, and Caia, and in an area south of the Zambezi River between Sena and Caia. With few exceptions on that date, CUI is 30 percent or less in the remaining portions of the study area. Overall, about 16 percent of the study area was cultivated on August 15, 1973, a time during which there were still large colonial agricultural activities operational but during which there may have been some guerilla activity in the area.
In May 1985, the amount of cropped area is estimated to have been 43 percent of the area cropped in 1973. Ten years after independence, collective farms had been established and guerilla warfare was being conducted by RENAMO in the study zone. Cropland Use Intensity was generally reduced to between 5 and 30 percent in areas where CUI had been in the range of 30-50 percent before independence (August 15, 1973). On May 11, 1985, large areas that in 1973 were cultivated between 5 and 30 percent were apparently uncultivated. It is notable that there was a substantial amount of open water along the Chire River just south of Malawi on May 11, 1985, in contrast to the smaller lakes in the same area on February 24, 1992, and even less standing water on the study dates in 1973, 1994, and 1995. Although there was apparently abundant water during the 19841985 cropping season, the civil war had continued since 1979, and it is possible that both postindependence agricultural practices and conflict in the area contributed to the reduced area cropped as of May 11, 1985.
By February 24, 1992, the Mozambican civil war had been waged for about 15 years. There had been major displacement and isolation of the population of the study area due to armed conflict, mining of roads, and sabotage of other infrastructure within the study area. The area was also hard hit by the 1991-1992 drought, which drove many people from their homes in search of food and water and seriously reduced crop production even for those who remained. The CUI interpreted from the TM scene of that date indicates only between 4 and 5 percent of the study area being cultivated, with very few, small areas 30 percent or more cultivated.
Following the signing of the Peace Accord in October 1992, refugees and displaced persons moved back into the study area, removal of mines began, inputs to agriculture (e.g., seeds and tools) began to be supplied to local people, and the normal agricultural rains arrived. The CUI interpretation of the May 28, 1994, TM scene indicates that the percentage of the study area under cultivation increased to about 10 percent. Most of the areas cropped between 30 and 50 percent on May 28, 1994, were west of the Zambezi River.
Analysis of the Mozambique Main Study Area shows a trend of decreasing crop production there from 1973 through 1992, the year in which the civil war ended. In comparison to CUI in the study area on February 24, 1992, 9 months before the Peace Accord was signed, CUI interpretation indicates that crop production had doubled 19 months after the Peace Accord was signed. Key factors in the increase in cropland use intensity are that the drought had ended, farmers had reentered the country, land mines were being removed, and inputs to agriculture were being contributed by donors.
Figure
3
Results: Substudy Area CUI -- Five Maps
Figure 3 focuses on a portion of the larger study area, the "substudy area," as defined by the smaller SPOT scene. The substudy area encompasses 253,756 hectares (about 50 km x 50 km, or one quarter of the 1,078,031-hectare study area). Twenty-two percent of the substudy area was cultivated in 1973, whereas only about 9 percent of the substudy area was estimated to have been cultivated as of May 11, 1985. During the 1991-1992 drought, and during one of the last months of the civil war, only 4 percent of the substudy area was estimated to have been cultivated. CUI interpretation of the February 24, 1992, subset of the TM scene covering the same area as the SPOT scene reveals that the conditions of warfare, mined roads, and drought resulted in very little crop production. As of May 28, 1994, hostilities had ceased, many of the roads in the substudy area had been cleared of land mines, refugees and displaced persons had returned, and development assistance and food aid were being provided by USAID and other donors. Agricultural production had increased to include 10 percent of the substudy area.
The CUI interpretation of the SPOT scene of April 20, 1995, shows about 17 percent of the substudy area under cultivation. The trend is clearly one of increase in crop production following the signing of the Peace Accord of October 1992. In April 1995, relatively intense cultivation (50-70 percent) is evident in some portions of the substudy area, south of the road between Sena and Tembe-Tembe.
Figure
4
Figure 4 depicts a decrease in cropped area within the study area subset, which includes an area approximately 50 km x 50 km, followed by an increase. Using the CUI interpretations of the five satellite images makes it possible to determine a general pattern of decreasing crop production, followed by increasing crop production. It is clear that crop production was severely decreased as a result of drought and effects of war, such as migration out of the area. Following the signing of the Peace Accord, it appears that crop production in the study area subset is increasing rapidly. This should result in improved nutrition of local people and increased demands for inputs to agriculture and transportation infrastructure (roads and vehicles) to ship agricultural products to markets outside the area.
Figure
5
Results: Change in Agricultural Intensity -- Two Maps
Between August 15, 1973, and February 24, 1992, crop production decreased in most of the study area subset, but there were increases in cropland use intensity in some areas west of the Zambezi River. Between February 24, 1992, and April 20, 1995, increases in cropland use intensity are evident along the Zambezi River and in alluvial soils associated with watercourses in the area. Decreases in cropland use intensity between 1992 and 1995 are seen in few, small, and scattered areas throughout the study area subset.
The changes in the intensity of cropping between February 24, 1992, and April 20, 1995, are, for most of the study area subset, increases. There are during that period, however, some portions of the study area subset for which cropland use intensity decreased. The reasons for decreases in CUI in some parts of the study area subset, in which overall there is a net increase in CUI, are not clear. It could be that marginal lands that had been cultivated were abandoned upon the cessation of hostilities in favor of more productive lands, or that as the peace holds over time, production areas shift from more isolated to more market-accessible locations.
The detailed map of the study area subset showing change in agricultural intensity between August 15, 1973, and February 24, 1992, also shows road status as of December 1994. It is assumed that all roads in the study area, which were indicated as Mined, De-Mining in progress, or De-Mining completed, were mined on February 24, 1992, 8 months before the Peace Accord was signed. Most of the area, and particularly the portions adjacent to mined roads, shows a substantial reduction in the use of the land for agriculture. There are notable exceptions in the westernmost parts of the scene. These areas, which historically did not contain any medium or large population centers, may have been more secure from land mines and isolated from hostilities than other parts of the study area.
In contrast, the scene representing change in agricultural intensity in the study area subset between February 24, 1992, and April 20, 1995, shows increases almost everywhere in the substudy area. Relatively large increases in cropland use intensity are evident in the area bounded by Charre, Sena, Tembe-Tembe, and the confluence of the Zambezi and Chire Rivers. The roads cleared of land mines as of December 1994 are also indicated, suggesting that removal of mines has been a major factor in enabling the inhabitants of the area to recommence crop production.
Conclusion
The use of cropland use intensity interpretation of satellite imagery of a portion of the Zambezi River Valley at different times over a period of 22 years shows dramatic differences in utilization of the land for agriculture. The devastating effects of war in virtually eliminating crop production in the study area are evident in maps derived from the interpretation of satellite imagery. On a brighter note, results of the October 1992 Peace Accord and subsequent assistance by USAID and other donors are evident in increased cultivation of land, the basis for economic activity in the study area. Periodic analysis of satellite images in the future can yield information about location of agricultural production and, with appropriate ancillary information, location of population.
