Drought Bulletin for the Greater Horn of Africa: Situation in June 2011

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1 Drought Bulletin for the Greater Horn of Africa: Situation in June 2011 Preliminary Analysis of data from the African Drought Observatory (ADO) SUMMARY The analyses of different meteorological and remote sensing indicators show that the territories currently most affected by drought are located between southern Somalia, southern Ethiopia, eastern Kenya, and north-eastern Tanzania (Fig. 1). This area was delimited considering the failure of the 2 previous rainy seasons (October-December 2010 and March-May 2011), which was reflected in severe anomalies in both meteorological and remote sensing indicators, implying a significant drought impact on vegetation, including crops. These indicators also highlighted a large area under threat between South Sudan, southern Sudan and western Ethiopia (Figure 1) where the peak of rainfall normally occurs in July but were already showing evidence of an impact on vegetation in recent months. The persistence of this situation could eventually lead to further drought related problems in these areas in the near future. Monitoring will continue to be undertaken in order to assess the situation in the months to come. Figure 1: Map of the drought most affected areas and areas under threat. Page 1 of 11

2 The severe impact of the drought affecting the Horn of Africa is not only due to the shortage of rain that has occurred since October 2010, but also to an unfavorable combination of different elements: poor crop harvests linked to rain seasonality, a second consecutive anomalously dry rainy season in southern Somalia, high population densities concentrated around the main cropping affected areas (Fig. 2), fighting and an unstable political situation forcing the suspension of humanitarian aid in some areas ( and an increase in food commodity prices ( As a result of this, the United Nations Office for the Coordination of Humanitarian Affairs has declared that a famine exists in two regions of southern Somalia, and has warned that the famine could soon spread to the rest of southern Somalia. Figure 2: Gridded Population of the World (adapted from SEDAC, 2009). Over the south-east of the Horn of Africa, roughly coinciding with the area most affected by the drought so far, the annual rainfalls are almost totally concentrated in two main rainy periods (Regions 2 and 3, Fig. 3): between September and November and between mid- March and mid-may. No irrigation is available in this area and therefore local food production is completely dependent on the rainfall. Due to the relatively short rainy periods the cultivated crops are mainly cereals characterized by fast growth (maize, millets, sorghum, etc.). The shortage of rain during the last two crop growing seasons contributed to the complete failure of the seasonal food production. The analysis of the SPI (Standardized Precipitation Index) over the last 25 years shows that although the rainfall shortage for the most recent rainy season (SPI-3, Fig. 5) was comparable to many previous events, it is the sustained rainfall shortage over the last 12 months that has made this event comparable only to droughts in 1992, 1994 and 2000/2001 (SPI-12, Fig. 9). Page 2 of 11

3 The effect of drought on the vegetation, including agricultural areas, is clearly shown on the analysis of the anomalies of two vegetation indicators (Figs 10 and 11), the fapar (fraction of Active Photosynthetic Active Radiation) and the NDWI (Normalized Difference Water Index). In this case, the analyses of the vegetation indicators show the highest impact on vegetation ever recorded since 1998 (Fig. 12). Figure 3: Rainfall regimes in the Greater Horn of Africa. [Left] Regions identified by rainfall based clustering; [Right] Long-term average monthly precipitations for each region (Period ). The integrated use of two different sources of information, meteorological and remote sensing data, shows great potential to synergistically monitor drought events in the Horn of Africa. The following sections present a more detailed overview of rainfall and of vegetation conditions, as registered by meteorological and remote sensing drought monitoring products. Overview of rainfall Short description of the rainfall index. Rainfall conditions are assessed using the Standardized Precipitation Index (SPI). The SPI provides a measure of the deviation of observed rainfall for a given location and accumulation period from normal conditions for that location and accumulation period. SPI values lower than -1.5 are indicative of severe drought, and values lower than -2 are indicative of extreme drought. For our analysis we use rainfall data from the Global Precipitation Climatology Centre (GPCC) [ reanalysis product for the years to define normal conditions and rainfall data from the GPCC monitoring (up to April 2011) and first guess (May June 2011) products for the observed rainfall. Page 3 of 11

4 Evolution of precipitation anomalies. The evolution of the SPI for 3-month rainfall accumulations (SPI-3) is shown in Figure 4. Severe drought conditions in terms of the SPI-3 began in eastern Kenya in October 2010 and spread eastwards to southern Somalia into the beginning of In April 2011 extreme drought conditions were evident in the Kenya-Somalia border region becoming more extreme by June A time series of the spatial average of SPI-3 for the most affected area from Figure 1, which corresponds to the rainfall region with peak rainfall in March, April, May (MAM) (Regions 2 and 3, Fig. 3), is shown in Figure 5. For the SPI-3 a more severe rainfall deficit was observed for MAM in 2000 than in 2011, although with more spatial variation, as shown by the error bars. This means that although some parts of the region experienced more severe rainfall deficits in MAM 2000, such severe rainfall deficits were not as widespread throughout the region compared to MAM The evolution of the SPI for 6-month (SPI-6) rainfall accumulations is shown in Figure 6. Severe drought conditions were evident in southern Ethiopia from September 2010 and continued to June 2011 becoming more widespread, with the most extreme conditions observed in the Somalia- Kenya border area and Uganda. The time series of the mean SPI-6 for the most affected area from Figure 1 shows that current conditions are comparable to previous 6-month rainfall deficits (Fig. 7), although a more extreme SPI-6 was observed in mid-2000, corresponding to the extreme SPI-3 value that was observed around the same time. The SPI-12 shows a similar evolution (Fig. 8). In July 2010, extreme 12-month drought conditions were already evident in Sudan and western parts of Ethiopia. Severe 12-month drought conditions began in southern Ethiopia around December 2010 January 2011 and spread throughout much of the Greater Horn of Africa by April The time series for mean SPI-12 for the most affected region from Figure 1 shows that current conditions are only comparable with the long-term rainfall deficit observed in 1992, 1994 and 2000/2001 (Fig. 9). Whilst rainfall deficits at seasonal timescales show that current conditions in the Greater Horn of Africa are comparable with recent short-term drought events, it is the sustained rainfall deficit evident from the SPI-12 that is causing the most concern for the region, and if such a deficit persists into the wet season for western Ethiopia and Sudan the situation could become much more severe for the Greater Horn of Africa region as a whole. Page 4 of 11

5 Figure 4: Evolution of the SPI for 3-month rainfall accumulations (SPI-3). Figure 5: Time series of the spatial average of SPI-3 for the most affected area (the vertical lines represent ± 1 standard deviation). Page 5 of 11

6 Figure 6: Evolution of the SPI for 6-month rainfall accumulations (SPI-6). Figure 7: Time series of the spatial average of SPI-6 for the most affected area (the vertical lines represent ± 1 standard deviation). Page 6 of 11

7 Figure 8: Evolution of the SPI for 12-month rainfall accumulations (SPI-12). Figure 9: Time series of the spatial average of SPI-12 for the most affected area (the vertical lines represent ± 1 standard deviation). Page 7 of 11

8 Overview of vegetation status Short description of the vegetation indices. Vegetation conditions in the Greater Horn of Africa were evaluated using two remote sensing derived indices: the fraction of Absorbed Photosynthetic Active Radiation, fapar, and the Normalized Difference Water Index, NDWI. fapar provides information related to the green biomass, while the NDWI is more related to the water content of the canopy. For both indices, anomalies were calculated for 10-day periods using the available data archives (fapar since 06/2002; NDWI since 04/1998). Anomalies lower than -1.0 are indicative of a moderate to severe vegetation stress. The NDWI dataset is derived from SPOT-VEGETATION instrument. Original images are provided in the frame of Geoland 2 and DevCoCast projects. Available archive starts in April The fapar dataset is derived from ENVISAT-MERIS instrument. Level 3 products are produced using the algorithm developed by JRC (Gobron et al., 2004) and distributed by European Space Agency, ESA. Available archive starts in June Monitoring of the vegetation conditions since October At the beginning of October 2010, the vegetation conditions as depicted by the fapar anomalies in the Horn of Africa were close to normal (Figure 10). In Mid-October and November, negative fapar anomalies began to be recorded in Somalia (central and southern parts), Ethiopia (mainly the south-eastern part) and in Kenya (northern and eastern parts). In December, the spatial extension of the drought as recorded by the fapar anomalies remained relatively constant, with a very spatially coherent negative signal registered for South Somalia. From January until the beginning of May 2011, fapar anomalies became more negative in the above mentioned regions. In terms of extent and intensity, the peak of the drought was observed between end of April and beginning of May. Additionally, negative fapar anomalies also began to be recorded in northern Tanzania (Figs 10 and 11). From May onwards, an improvement of the vegetation conditions was observed in Ethiopia while the fapar anomalies remained negative in Somalia and Kenya (Fig. 11). The particularly poor vegetation conditions in Somalia and northern Kenya can be seen to be a result of the shortage of rainfall during the rainy season of March to May (Regions 2 and 3, Fig. 3). Time series of spatially averaged fapar and NDWI anomalies were extracted for the most affected area, comprising Somalia, Ethiopia and Kenya (Fig. 12). For both vegetation indices, the current drought is the most severe recorded during the available time series (largest negative anomalies). Although the archives of the vegetation indexes are relatively short (NDWI, from 04/ /2011 ; fapar, from 06/ /2011), it can be seen that the current drought is quite exceptional in terms of impact on the vegetation in this area. Reference: Gobron N., Aussedat O., Pinty B., Taberner M., and Verstraete M. M Medium Resolution Imaging Spectrometer (MERIS) - An optimized FAPAR Algorithm - Theoretical Basis Document. Revision 3.0. Institute for Environment and Sustainability, EUR Report No EN, 20p. Page 8 of 11

9 Figure 10: fapar 10-day anomaly from October 2010 to January Green corresponds to positive anomalies (vegetation greener than normal), white to near-normal vegetation conditions and yellow and red to negative anomalies (vegetation less green than normal). Grey corresponds to no data. The image of the 3 rd 10-day period of October 2010 is missing. Page 9 of 11

10 Figure 11: fapar 10-day anomaly from March 2011 to June Green corresponds to positive anomalies (vegetation greener than normal), white to near-normal vegetation conditions and yellow and red to negative anomalies (vegetation less green than normal). Grey corresponds to no data. The images of February and of the 3 rd 10-day period of October 2010 are missing. Page 10 of 11

11 Figure 12: Time series of the spatial average of fapar and NDWI anomalies for the most affected area (the vertical lines represent ± 1 standard deviation). European Communities, 2011 JRC Produced by: European Commission (EC) Joint Research Centre (JRC) - IES Institute Land Management and Natural Hazards Unit, DESERT Action,TP280, Ispra (VA), Italy Contact: Jürgen Vogt (Action Leader) juergen.vogt@jrc.ec.europa.eu Bulletin authors: Paulo Barbosa, Stéphanie Horion, Fabio Micale and Andrew Singleton. Disclaimer: The geographic borders are purely a graphical representation and are only intended to be indicative. These boundaries do not necessarily reflect the official EC position. Legal Notice: Neither the European Commission nor any person acting on behalf of the Commission is responsible for the use, which might be made of this publication. Reproduction is authorized provided the source is acknowledged. Page 11 of 11