Analysis of Slope and Landuse Relationships in Eastern Luangwa Valley Dr. Conrad Heatwole Center for Watershed Studies Virginia Tech, Blacksburg

Study watersheds – Magodi Stream gage Weather station Rain gage Manual raingage

Paired Forest/Ag. Watersheds Khuyu school Forested watershed Chazovu school Kamwamphula Agricultural watershed Watersheds are similar size, similar slopes and landscape position, side-by-side, but with quite different land use. (although the “forested” watershed is quickly being cleared.) Luelo ZAWA gate

Cropland expansion 1989-2007 1989 Landsat We will look next at the change in clearing that has occurred in the past 18 years… Note that the Luelo watershed is largely cleared, Note that Kamwampula watershed (west) is almost completely forested.

Cropland expansion 1989-2007 2002 Landsat Notice the increased cleared areas in the forested watershed. 13 years of change – but next 5 years are more dramatic..

Cropland expansion 1989-2007 2007 Ikonos Continued clearing. Greater expansion 2002-2007 than from 1989-2002. (unfortunately some clouds in the way)

Cropland expansion 1989-2007 Cropland expansion 1989-2007 1989 Landsat Another way to look at the change from 1989 – 2007 directly using the ENSO Mosaic digitized parcels

Cropland expansion 1989-2007 1989 Landsat Polygons are cleared areas on May 2007 EnsoMosaic 1989 Landsat Toggle back and forth with previous slide

Slope map of area Slope (%) Paired watersheds Dambo watersheds 0-4 4-8 8-15 15-30 30-45 > 45 Note the difference in slopes for the plateau, forest/hill region, and valley floor NOTE the “paired watersheds” in the hill region – mostly 4-8% slopes and higher, compared to ‘Dambo watersheds’ which are almost completely under 4% slope. Dambo watersheds Paired watersheds Slope calculated from 30m elevation grid derived from SRTM data using cubic interpolation.

Relation of cleared areas to landscape position Maps of elevation and slope with the Enso cleared areas overlayed

Relationship between slope and cleared areas Cleared areas (digitized from 2007 Enso/Mosaic aerial imagery as seen in above slides) are overlaid on the slope map. Slope data is classified in 1% increments. Areas at different slope values are tabulated. Cumulative areas determined and graphed as a % of the area.

Comparing slopes of cleared land in hill and plateau regions Graph of cumulative percent area less than a certain slope Data is only for cleared area on the 2007 Enso/Mosaic Example – at 4% slope: 45% of hill area and 83% of plateau area is less than 4% Conversely, 55% of hill area is greater than 4% slope, but only 17% of the plateau area. Graph shows the distribution of slope for the cleared areas of the plateau and hill regions (in the 2007 Enso/Mosaic data). The curves show the % of area less than the indicated slope. Thus, we can start on the vertical axis and note that at 70% the ‘Plateau’ curve value is approximately 3% and the ‘Hill’ value is approximately 5.5%. Thus, 70% of the plateau cleared area is less than 3% slope while 70% of the cleared Hill area is less than 5.5% slope. We can also consider the inverse – noting that 30% of the cleared plateau area is GREATER than 3% slope, while 30% of the cleared hill area is greater than 5.5%. Beginning on the horizontal axis is perhaps more informative. Lets pick the 3% slope and look up to the ‘Hills’ curve which has a value of approx 30% meaning that 30% of the area is less than 3% slope, and conversely, that 70% of the cleared hill area is greater than 3%. Continuing up to the ‘Plateau’ curve, the value is approximately 70%, meaning that only 30% of the area is greater than 3% slope. Thus, the cleared area greater than 3% slope is 30% of the plateau and 70% of the hill regions. Cumulative distribution of cleared area based on slope

Comparing slopes of cleared land for three watersheds Observations: Kamwamphula is steeper than Luelo; both are much steeper than the plateau area While about 13% of the plateau watershed is greater than 4% slope, 45 to 60% of the hill area is Cleared areas tend to the lower slopes, but surprisingly represent the range of slopes in the watershed. cleared areas are not exclusively on the low slopes The curves for the more fully cleared Luelo are closest, indicating that over time, cleared land represents the whole watershed – not just flatter areas The curves for Kamwamphula are further apart, showing that initial clearing is on flatter areas. However, the trend seen in the Luelo is to be expected. Graph shows the distribution of slope for the Luelo and Kamwamphula watersheds, for the total watershed area and for the cleared area. and for the combined area of the two dambo watersheds (Kanyanga and Mphiri). The curves show the % of area less than the indicated slope. Cumulative distribution of area based on slope for a plateau watershed and two watersheds in the hill region