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Long-term drought assessment of Northern Central African continent using Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST). Course: CSI-655 Date: May 16, 2011 Taeyoung (Jason) Choi. Outline. Motivation Introduction Drought and indices
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Long-term drought assessment of Northern Central African continent using Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) Course: CSI-655 Date: May 16, 2011 Taeyoung (Jason) Choi
Outline • Motivation • Introduction • Drought and indices • LST-NDVI combined index • Data sets and Methodology • About MODIS • LST product • NDVI product • Methodology • Characteristics of Regions of Interest (ROI) • Results • NDVI Responses • LST Responses • LST-NDVI Responses • Summary
Motivation • Africa continent is facing climate changes. • Drought is the main problem. • Drought condition could be detected by remotely sensed data especially from MODIS. • This study is focused on drought conditions from Terra MODIS collections over a decade. • In selected locations in Northern Central Africa • Near ‘Sahel’ region
Introduction • Drought • prolonged insufficient in reasonable water supply beyond the range of normal human activities. • Drought monitored by metrological precipitation record. • Data sets were not uniformly distributed in time and space. • Remotely sensed data sets became a promising source.
Introduction • Remotely Sensed data sets as a drought index. • Normalize Difference Vegetation Index (NDVI) • Land Surface Temperature (LST) • from the thermal infrared signature received by satellite sensors • widely implemented as a proxy for vegetation condition and combined with NDVI
Introduction • Remotely Sensed data sets as a drought index. • NDVI-LST combined relationship • ‘Universal triangle’ relationship
Data sets and Methodology • About Moderate Resolution Imaging Spectroradiometer (MODIS) Terra (EOS-AM): Launched on 12/18/99 First light on 02/24/00
Data sets and Methodology • MODIS Land Products • Vegetation indices product MOD13 (130 scenes) • LST measures land surface temperature and emissivity (MOD11 130 scenes)
Data sets and Methodology • Methodology • NDVI monitoring • LST monitoring • NDVI-LST relationship monitoring • Slopes and y-crossing points.
Regions of Interest (ROI) • ROIs are located around the border between Chad and Central Africa Republic • Size of 2 degrees by 2 degrees • Latitudes of 8 degrees, 10 degrees and 12 degrees with a fixed longitude of 20 degrees
Regions of Interest (ROI) • These ROIs are perpendicular to the direction of ‘Sahel’ region. • Between Sahara desert from the north and humid forest region. • Environmentally very sensitive. [11] World Resources Institute (Lead Author);LeszekBledzki (Topic Editor) "Ecosystems and Human Well-being: Desertification Synthesis: Key Questions on Desertification in the Millennium Ecosystem Assessment". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland, Retrieved April 28, 2011
Results • NDVI and LST from 2000 to 2010
Results • NVDI-LST responses
Maximum temperature drop in May from LST. • Dry season: decreasing slope & stable Temp. • Wet season: increasing slope & decreasing Temp.
Summary • 11 years of monthly MODIS NDVI and LST data sets were used to detect central Africa drought condition. • Dry Season • Decreasing slope with stable temperature • Getting drier • Wet Season • Increasing slope with temperature drop • Getting more humid • More extreme events are expected in the future. • The NDVI-LST relationship provided much stable and comprehensive information on drought conditions.
