Long-term drought assessment of Northern Central African continent using Normalized

Difference Vegetation Index (NDVI) and Land Surface Temperature (LST)

Course: CSI-655Date: 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

RNIR

RNIRNDVI

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 12/18/99First 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);Leszek Bledzki (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.

Backup Slides

Results (NDVI)

Results (LST)

Results (NDVI-LST : Slope)

Results (NDVI-LST : Y-crossing point)