Abstract
As the world population keeps increasing and cultivating more land, the extraction of vegetation conditions using remote sensing is important for monitoring land changes in areas with limited ground observations. Water supply in wetlands directly affects plant growth and biodiversity, which makes monitoring drought an important aspect in such areas. Vegetation Temperature Condition Index (VTCI) which depends on thermal stress and vegetation state, is widely used as an indicator for drought monitoring using satellite data. In this study, using clear-sky Landsat multispectral images, VTCI was derived from Land Surface Temperature (LST) and the Normalized Difference Vegetation Index (NDVI). Derived VTCI was used to observe the drought patterns of the wetlands in Lake Chad between 1999 and 2018. The proportion of vegetation from WorldView-3 images was later introduced to evaluate the methods used. With an overall accuracy exceeding 90% and a kappa coefficient greater than 0.8, these methods accurately acquired vegetation training samples and adaptive thresholds, allowing for accurate estimations of the spatially distributed VTCI. The results obtained present a coherent spatial distribution of VTCI values estimated using LST and NDVI. Most areas during the study period experienced mild drought conditions, though severe cases were often seen around the northern part of the lake. With limited in-situ data in this area, this study presents how VTCI estimations can be developed for drought monitoring using satellite observations. This further shows the usefulness of remote sensing to improve the information about areas that are difficult to access or with poor availability of conventional meteorological data.
Highlights
Marshes and vegetation close to inland water bodies are known to be sensitive to changes in hydrology within their natural habitat since they co-exist in transitional zones between aquatic and terrestrial systems
The averaged Overall Accuracy (OA) of vegetation proportions detected during our two test periods was greater than 90% mostly due to the relative ease of identifying vegetation feature within the area (Figures 5 and 6)
While policies for proper management of the lake are being put in place by the Lake Chad Basin Commission (LCBC) to ensure sustainable management of this water resource, we suggest that the influences of atmosphere and other additional channels on drought in this area should be investigated over a longer period
Summary
Marshes and vegetation close to inland water bodies are known to be sensitive to changes in hydrology within their natural habitat since they co-exist in transitional zones between aquatic and terrestrial systems. Given that marshes and vegetation close to inland water bodies are tied to the availability of water within their ecosystem, identification of drought patterns could be used as a tool for monitoring and sustainable management [6]. Drought monitoring becomes a hurdle in cases where the wetland and marshes are in hard-to-reach areas and with occasional unfavorable flooding conditions. This coupled with limited and low-quality ground observations hinders effective drought monitoring for a given area
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