Monitoring Live Vegetation in Semiarid Rangelands of Kenya

Submitted by atripp on Wed, 04/01/2020 - 14:50

As part of the U.S. Department of the Interior’s (DOI) commitment to provide technical assistance to the Kenyan Northern Rangelands Trust (NRT), the USGS created a high spatial and time-sensitive live vegetation monitoring system in collaboration with the DOI International Technical Assistance Program and the U.S. Agency for International Development’s (USAID’s) regional mission in East Africa. The NRT works to protect iconic species such as elephants, rhinos, and cheetahs while supporting a pastoral population dependent on access to grazing areas for livestock. The developed mapping system provides temporal and spatial variability of live grassland cover that is key information to support proactive management to maximize livestock and wildlife grazing use and avoid conflict.

Sentinel-2 satellite data were selected for mapping the dynamics of grassland live fractional cover (LFC) because they have a 10-meter spatial resolution and a 5- to 7-day repeat collection cycle. The grassland LFC mapping protocol proceeded in steps. First, specialized field technologies collected field-modified, soil-adjusted vegetation index-2 (field-MSAVI2) data and coincident field measurements of grassland LFC.  Field-MSAVI2 data were correlated to LFC data using linear regression, resulting in a ±10% prediction accuracy. Next, satellite-based Sentinel-2 MSAVI2 data (calculated from the Sentinel-2 image data) were calibrated to the field-MSAVI2 data at a 92% confidence. Finally, the calibrated Sentinel-2 MSAVI2 data were used to create LFC maps.

The resulting LFC maps representing times of severe drought, average rainfall, and seasonally dry periods depict the expected region-wide status and changes while reproducing the high spatial diversity of the rangeland grassland landscape. Map interpretability was enhanced by representing LFC as a fraction between 0 and 100 as well as creating a tree mask overlay. An important objective was to provide a framework conducive for transfer of all components of the mapping to NRT. To provide that framework, mapping is based on free satellite image data that can be processed with free software downloaded to a personal workstation. The maps are produced in a format directly compatible with standard geographic information system software. Transfer of that mapping technology to NRT is underway.

(Top Left) The core-Northern Rangelands Trust mapped region that includes 17 Conservancies and Reserves in northern Kenya. (Bottom) A map product example (centered approximately at 37° 14’ 16.8178” E, 0° 50’ 15.0359” N) depicting June 2018 Live Fractional Cover (LFC) status (A) without and (B) with the tree mask overlay (dark green). (C) September 2017 to June 2018 LFC change with tree mask overlay (dark green), and (D) Google Earth image on May 2011. Arrows locate small-scale pastoral settlements identified on figure D that are highlighted by the tree mask in figures B and C.

Author Name
Amina Rangoonwala
Author Email