Abstract
Abstract. Drought in East Africa is a recurring phenomenon with significant humanitarian impacts. Given the steep climatic gradients, topographic contrasts, general data scarcity, and, in places, political instability that characterize the region, there is a need for spatially distributed, remotely derived monitoring systems to inform national and international drought response. At the same time, the very diversity and data scarcity that necessitate remote monitoring also make it difficult to evaluate the reliability of these systems. Here we apply a suite of remote monitoring techniques to characterize the temporal and spatial evolution of the 2010–2011 Horn of Africa drought. Diverse satellite observations allow for evaluation of meteorological, agricultural, and hydrological aspects of drought, each of which is of interest to different stakeholders. Focusing on soil moisture, we apply triple collocation analysis (TCA) to three independent methods for estimating soil moisture anomalies to characterize relative error between products and to provide a basis for objective data merging. The three soil moisture methods evaluated include microwave remote sensing using the Advanced Microwave Scanning Radiometer – Earth Observing System (AMSR-E) sensor, thermal remote sensing using the Atmosphere-Land Exchange Inverse (ALEXI) surface energy balance algorithm, and physically based land surface modeling using the Noah land surface model. It was found that the three soil moisture monitoring methods yield similar drought anomaly estimates in areas characterized by extremely low or by moderate vegetation cover, particularly during the below-average 2011 long rainy season. Systematic discrepancies were found, however, in regions of moderately low vegetation cover and high vegetation cover, especially during the failed 2010 short rains. The merged, TCA-weighted soil moisture composite product takes advantage of the relative strengths of each method, as judged by the consistency of anomaly estimates across independent methods. This approach holds potential as a remote soil moisture-based drought monitoring system that is robust across the diverse climatic and ecological zones of East Africa.
Highlights
The 2010–2011 Horn of Africa drought affected over 13 million people (Ledwith, 2011)
We examine the 2010–2011 Horn of Africa drought using remotely sensed estimates of soil moisture, evapotranspiration, precipitation, and terrestrial water storage
FEWS NET determined that the total anomaly in precipitation during the 2010–2011 rainy seasons was the most severe in the last 50 yr for parts of Kenya and Ethiopia (USAID FEWS NET, 2011)
Summary
The 2010–2011 Horn of Africa drought affected over 13 million people (Ledwith, 2011). The failure of the October to December 2010 “short” rains and delayed arrival of the April to June 2011 “long” rains caused crop failures across Somalia, Ethiopia and Kenya. On 7 June 2011, the Famine Early Warning System Network (FEWS NET) issued a statement declaring the crisis to be “the most severe food security emergency in the world today”. Over the course of the two months, the crises worsened and the United Nations declared famine in five regions of Somalia (United Nations, 2011). The emerging La Nina event in summer 2010, occurring on top of steady Indian Ocean warming that has been associated with reduced precipitation in the Horn of Africa, and combined with weakened social
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