Assaf Anyamba

Oak Ridge National Laboratory

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Compton J. Tucker

Goddard Space Flight Center

Jennifer Small

Goddard Space Flight Center

Kenneth J. Linthicum

Center for Medical, Agricultural and Veterinary Entomology

Seth C. Britch

United States Department of Agriculture

Ed Pak

Goddard Space Flight Center

William B. Karesh

EcoHealth Alliance

Rasmus Fensholt

University of Copenhagen

Jean-Paul Chrétien

Smithsonian Conservation Biology Institute

Inge Sandholt

Technical University of Denmark

Brett M. Forshey

Armed Forces Health Surveillance Center

Cooperative Institutions

Goddard Space Flight Center

Kenya Medical Research Institute

University of Maryland, College Park

United States Department of Agriculture

Uniformed Services University of the Health Sciences

Stanford University

Walter Reed Army Institute of Research

University of Copenhagen

University of Florida

National Aeronautics and Space Administration

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Seasonal to interannual variability of vegetation and fires at SAFARI 2000 sites inferred from advanced very high resolution radiometer time series data

Journal of Geophysical Research Atmospheres (2003)

Assaf Anyamba C. O. Justice Compton J. Tucker Robert Mahoney

NOAA advanced very high resolution radiometer data are used to place the SAFARI 2000 and SAFARI 1992 intensive campaigns in the context of the interannual variability of vegetation conditions in southern Africa. Normalized difference vegetation index (NDVI) measurements and sea surface temperature (SST) indices of El Niño/Southern Oscillation (ENSO) are compared and the connections explained. The paper shows the vegetation evolution for the 2000 growing season, with unprecedented high and persistent NDVI anomalies associated with a cold phase of ENSO (La Niña) and above average rainfall between November and May, south of 15°S. In contrast, the 1992 season showed marked negative NDVI anomalies associated with an extreme drought in the southern part of the region, associated with the warm phase of ENSO (El Niño). These differences in NDVI patterns resulted in different patterns of fire distribution. More satellite detections of active fires were observed in 2000 than in 1992, especially for Botswana, Namibia, southern Zimbabwe, and southern Mozambique. Comparisons between in situ airborne measurements collected in 2000 and 1992 require an understanding of the extremely different vegetation and fire conditions associated with those years. Generalizations from results of the two SAFARI campaigns should be made with careful consideration of the extreme differences in conditions and the large interannual variability encountered in southern Africa, as depicted by the long‐term record of satellite vegetation measurements.

Advanced very-high-resolution radiometer

10.1029/2002jd002464

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Evaluation of Extreme Soil Moisture Conditions During the 2020 Sahel Floods and Implications for Disease Outbreaks

Geophysical Research Letters (2022)

N. Thomas Assaf Anyamba Heidi Tubbs Bhaskar Bishnoi

Abstract The June‐October 2020 growing season was characterized by sustained and extreme flooding across the African Sahel. One consequence of flooding events such as this is outbreaks of vector borne diseases (VBDs) which are often associated with climate anomalies. In this study, data from the soil moisture active passive (SMAP) mission is used with other soil moisture and precipitation data to show that the 2020 Sahelian growing season was the most extreme over the past four decades, ranking first in seasonally accumulated precipitation, which on average exceeded the climatology by around 300 mm. VBD outbreaks of Rift Valley fever and Chikungunya followed in Mauritania/Senegal and Chad, respectively. In some cases, soil moisture is a better indicator of VBD outbreak risk than precipitation, which has so far been more commonly used in studies of VBD outbreaks. It is expected that this finding will inform future monitoring and prediction efforts for VBD risk.

10.1029/2022gl099872

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NDVI anomaly patterns over Africa during the 1997/98 ENSO warm event

International Journal of Remote Sensing (2001)

Assaf Anyamba Compton J. Tucker J. Ronald Eastman

Normalized Difference Vegetation Index (NDVI) departure patterns for Africa during the 1997/98 El Niño/Southern Oscillation (ENSO) warm event show two dominant patterns. Over equatorial Eastern Africa, above normal NDVI anomalies persisted from October 1997 through the normal dry season (December-February) and into the long rains season in March-May. Over Southern Africa the spatial NDVI anomaly shows a dry western half and a relatively greener than normal eastern half. Correlations between the temporal NDVI anomalies with ENSO indices shows that the anomalous conditions over Eastern Africa were a direct result of anomalous warming of sea surface temperatures (∼+3°C) in the western equatorial Indian Ocean (WIO) and a lagged response to the warming in the eastern Pacific Ocean (+4°C). We suggest that this anomalous warming of the WIO and the equatorial eastern Atlantic Ocean basin dampened the normal severe drought response pattern over Southern Africa where mild drought conditions were experienced. The overall continental response pattern shows a meridional dipole pattern, with above normal NDVI straddling the equator between 10° N and 10° S and normal to slightly below normal NDVI south of 15° S, predominantly over south-western Africa.

Anomaly (physics)

10.1080/01431160010029156

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Linkages between GRACE water storage, hydrologic extremes, and climate teleconnections in major African aquifers

Environmental Research Letters (2021)

Bridget R. Scanlon Ashraf Rateb Assaf Anyamba Seifu Kebede Alan MacDonald

Abstract Water resources management is a critical issue in Africa where many regions are subjected to sequential droughts and floods. The objective of our work was to assess spatiotemporal variability in water storage and related controls (climate, human intervention) in major African aquifers and consider approaches toward more sustainable development. Different approaches were used to track water storage, including GRACE/GRACE Follow On satellites for Total Water Storage (TWS); satellite altimetry for reservoir storage, MODIS satellites for vegetation indices, and limited ground-based monitoring. Results show that declining trends in TWS (60–73 km 3 over the 18 yr GRACE record) were restricted to aquifers in northern Africa, controlled primarily by irrigation water use in the Nubian and NW Saharan aquifers. Rising TWS trends were found in aquifers in western Africa (23–49 km 3 ), attributed to increased recharge from land use change and cropland expansion. Interannual variability dominated TWS variability in eastern and southern Africa, controlled primarily by climate extremes. Climate teleconnections, particularly El Nino Southern Oscillation and Indian Ocean Dipole, strongly controlled droughts and floods in eastern and southern Africa. Huge aquifer storage in northern Africa suggests that the recent decadal storage declines should not impact the regional aquifers but may affect local conditions. Increasing groundwater levels in western Africa will need to be managed because of locally rising groundwater flooding. More climate resilient water management can be accomplished in eastern and southern Africa by storing water from wet to dry climate cycles. Accessing the natural water storage provided by aquifers in Africa is the obvious way to manage the variability between droughts and floods.

Teleconnection

Water storage

10.1088/1748-9326/ac3bfc

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Selected wetland soil properties correlate to Rift Valley fever livestock mortalities reported in 2009-10 in central South Africa

PLoS ONE (2020)

Anna M. Verster Janice E. Liang Melinda K. Rostal Alan C. Kemp Robert F. Brand

Outbreaks of Rift Valley fever have devastating impacts on ruminants, humans, as well as on regional and national economies. Although numerous studies on the impact and outbreak of Rift Valley fever exist, relatively little is known about the role of environmental factors, especially soil, on the aestivation of the virus. This study thus selected 22 sites for study in central South Africa, known to be the recurrent epicenter of widespread Rift Valley fever outbreaks in Southern Africa. Soils were described, sampled and analyzed in detail at each site. Of all the soil variables analyzed for, only eight (cation exchange capacity, exchangeable Ca2+, exchangeable K+, exchangeable Mg2+, soluble Ca2+, medium sand, As, and Br) were statistically identified to be potential indicators of sites with reported Rift Valley fever mortalities, as reported for the 2009–2010 Rift Valley fever outbreak. Four soil characteristics (exchangeable K+, exchangeable Mg2+, medium sand, and Br) were subsequently included in a discriminant function that could potentially be used to predict sites that had reported Rift Valley fever-associated mortalities in livestock. This study therefore constitutes an initial attempt to predict sites prone to Rift Valley fever livestock mortality from soil properties and thus serves as a basis for broader research on the interaction between soil, mosquitoes and Rift Valley fever virus. Future research should include other environmental components such as vegetation, climate, and water properties as well as correlating soil properties with floodwater Aedes spp. abundance and Rift Valley fever virus prevalence.

Rift Valley Fever

Rift valley

10.1371/journal.pone.0232481

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Citations (6)

Recent trends in vegetation dynamics in the African Sahel and their relationship to climate

Global Environmental Change (2005)

Stefanie Herrmann Assaf Anyamba Compton J. Tucker

Desertification

10.1016/j.gloenvcha.2005.08.004

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Citations (828)

Global Trends in Seasonality of Normalized Difference Vegetation Index (NDVI), 1982–2011

Remote Sensing (2013)

J. Ronald Eastman Florencia Sangermano Elia Machado de Oliveira John Rogan Assaf Anyamba

A 30-year series of global monthly Normalized Difference Vegetation Index (NDVI) imagery derived from the Global Inventory Modeling and Mapping Studies (GIMMS) NDVI3g archive was analyzed for the presence of trends in changing seasonality. Using the Seasonal Trend Analysis (STA) procedure, over half (56.30%) of land surfaces were found to exhibit significant trends. Almost half (46.10%) of the significant trends belonged to three classes of seasonal trends (or changes). Class 1 consisted of areas that experienced a uniform increase in NDVI throughout the year, and was primarily associated with forested areas, particularly broadleaf forests. Class 2 consisted of areas experiencing an increase in the amplitude of the annual seasonal signal whereby increases in NDVI in the green season were balanced by decreases in the brown season. These areas were found primarily in grassland and shrubland regions. Class 3 was found primarily in the Taiga and Tundra biomes and exhibited increases in the annual summer peak in NDVI. While no single attribution of cause could be determined for each of these classes, it was evident that they are primarily found in natural areas (as opposed to anthropogenic land cover conversions) and that they are consistent with climate-related ameliorations of growing conditions during the study period.

Seasonality

Shrubland

Biome

Growing season

10.3390/rs5104799

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Citations (239)

Prediction of a Rift Valley fever outbreak

Proceedings of the National Academy of Sciences (2009)

Assaf Anyamba Jean-Paul Chrétien Jennifer Small Compton J. Tucker Pierre Formenty

El Niño/Southern Oscillation related climate anomalies were analyzed by using a combination of satellite measurements of elevated sea-surface temperatures and subsequent elevated rainfall and satellite-derived normalized difference vegetation index data. A Rift Valley fever (RVF) risk mapping model using these climate data predicted areas where outbreaks of RVF in humans and animals were expected and occurred in the Horn of Africa from December 2006 to May 2007. The predictions were subsequently confirmed by entomological and epidemiological field investigations of virus activity in the areas identified as at risk. Accurate spatial and temporal predictions of disease activity, as it occurred first in southern Somalia and then through much of Kenya before affecting northern Tanzania, provided a 2 to 6 week period of warning for the Horn of Africa that facilitated disease outbreak response and mitigation activities. To our knowledge, this is the first prospective prediction of a RVF outbreak.

Rift Valley Fever

10.1073/pnas.0806490106

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Citations (336)

Midwest agriculture and ENSO: A comparison of AVHRR NDVI3g data and crop yields in the United States Corn Belt from 1982 to 2014

International Journal of Applied Earth Observation and Geoinformation (2018)

Erin Glennie Assaf Anyamba

A time series of Advanced Very High Resolution Radiometer (AVHRR) derived normalized difference vegetation index (NDVI) data were compared to National Agricultural Statistics Service (NASS) corn yield data in the United States Corn Belt from 1982 to 2014. The main objectives of the comparison were to assess 1) the consistency of regional Corn Belt responses to El Niño/Southern Oscillation (ENSO) teleconnection signals, and 2) the reliability of using NDVI as an indicator of crop yield. Regional NDVI values were used to model a seasonal curve and to define the growing season — May to October. Seasonal conditions in each county were represented by NDVI and land surface temperature (LST) composites, and corn yield was represented by average annual bushels produced per acre. Correlation analysis between the NDVI, LST, corn yield, and equatorial Pacific sea surface temperature anomalies revealed patterns in land surface dynamics and corn yield, as well as typical impacts of ENSO episodes. It was observed from the study that growing seasons coincident with La Niña events were consistently warmer, but El Niño events did not consistently impact NDVI, temperature, or corn yield data. Moreover, the El Niño and La Niña composite images suggest that impacts vary spatially across the Corn Belt. While corn is the dominant crop in the region, some inconsistencies between corn yield and NDVI may be attributed to soy crops and other background interference. The overall correlation between the total growing season NDVI anomaly and detrended corn yield was 0.61(p = 0.00013), though the strength of the relationship varies across the Corn Belt.

10.1016/j.jag.2017.12.011

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Analysing the advantages of high temporal resolution geostationary MSG SEVIRI data compared to Polar Operational Environmental Satellite data for land surface monitoring in Africa

International Journal of Applied Earth Observation and Geoinformation (2011)

Rasmus Fensholt Assaf Anyamba S. Huber Simon Proud Compton J. Tucker

Polar orbit

Earth observation

Temporal resolution

Environmental Monitoring

10.1016/j.jag.2011.05.009

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Citations (47)