Chris Funk, Gideon Galu, Greg Husak, Will Turner, Juliet Way-Henthorne
An analysis of mid-season rainfall, WRSI simulations, and crop statistics indicate a high probability of a very poor Somali Deyr 2018 growing season. Rainfall deficits in Kenya also indicate poor growing conditions.
FEWS NET food security outlooks rely on a series of information products. Before the growing season, an analysis of climate modes and climate forecasts provides an evidence-based foundation for seasonal rainfall outlooks. By mid-season, however, rainfall observations, crop and hydrology models, and other forms of monitoring provide more detailed and accurate sources of information. These information sources can be especially powerful in areas with short growing seasons (such as Somalia), where arid conditions create a short window for successful harvests. FEWS NET science partners have been steadily improving our monitoring resources, and here, we use some of these products to assess likely agroclimatic outcomes for the Somali 2018 Deyr growing season. Crop statistics, provided by the FEWS NET data warehouse, allow us to further leverage these resources to provide quantitative projections of Maize/Sorghum crop production values. While not as accurate as post-harvest assessments, these preliminary rainfall-based projections suggest that a poor cropping season is very likely. Poor pasture conditions also seem probable for some regions.
Poor seasonal rainfall performance
Dry conditions appear extremely likely over southern Somalia and most of Kenya. Note the large discrepancy between the ARC2 (Fig. 1-left) and CHIRPS (Fig 1-right) results over Eastern Ethiopia. CHIRPS incorporates additional station data provided by the Ethiopian Meteorological Agency and is much more representative of the current situation in eastern Somalia. Rainfall estimates from CPC’s ARC2 archive and the USGS/CHC’s CHIRPS2 data sets converge on similar outlooks for a very dry October-December growing season for Somalia (Figure 1). The CPC provides Seasonal Rainfall Performance Probability (SPP) Analyses for October-December. These analyses use observed ARC2 data up to the present and then completes the remainder of the season with all previous historical ARC2 observations. This enables them to estimate the probable seasonal outcome (Figure 1, left). Based on the SPP analysis through mid-November, most of Somalia (including the main crop growing areas) are very likely (>75% chance) to receive below-normal rainfall. The USGS/CHC has also recently started producing an “Early Estimate” product that combines observed CHIRPS data with CHIRPS-compatible 10-day GEFS rainfall forecasts. The right panel of Figure 1 shows Early Estimate rainfall anomalies for October 1 through November 25th. Dry conditions appear extremely likely over southern Somalia and most of Kenya.
Figure 1. Left – CPC Seasonal Precipitation Performance predictions for October-December 2018. Right – CHC Early Estimate seasonal rainfall anomalies.
Somalia Deyr Rainfall and Crop Production Projections
Next, we examine in detail rainfall averaged across crop-growing zones in Bay, lower, and middle Shabelle districts (Figure 2). These rainfall estimates combine October and the 1st two dekads of November, with CHIRPS-GEFS forecasts used to fill in dekad 2 of November. For 2018, these seasonal totals look very low, almost identical with previous signature drought years: 1998, 1999, 2003, 2005, 2010, and 2016.
Figure 2. October 1-November 20 CHIRPS observations for the main Somali crop growing regions.
Using historical sorghum and sorghum+maize crop production data from the FEWS NET data warehouse, we can use logistic regression to relate these seasonal rainfall totals to 1995-2016 Deyr seasonal production estimates (Figure 3). We treat sorghum separately because we found that it had a very strong relationship with rainfall (R2~0.7). We also provide maize+sorghum total production projections to support food security analyses. It should be noted that these projections are not intended to replace careful post-harvest crop assessments, but, rather, as an advanced outlook on the general pattern such assessments are likely to indicate. We have excluded 1997 and 2011 from our estimation procedure, because 1997 was an exceptionally wet year with modest production (presumably due to flooding), while 2011 was a normal rainfall year with low crop production (presumably due to conflict).
One of the most notable features of Figure 3 is the non-linear relationship between rainfall and crop production. Below 100 mm of rainfall, crop production drops very quickly. A 2018 rainfall total of ~60 mm indicates poor crop production. Using take-one-away cross-validation and regression, we have estimated the 2018 Deyr Sorghum and Sorghum+Maize production totals as 45 and 81 thousand metrics tons. These estimates correspond to ~50% and 60% of the 2012-2016 average production (i.e. production about half of the recent average production). Eighty percent confidence intervals, based on the cross-validation results, indicate ranges of 43-46 and 77 to 83 thousand metric tons for Deyr Sorghum and Sorghum+Maize production. Note that the late November rainfall estimates are based on weather model forecasts, and there is still room for the season to improve; however, the overall outlook is very pessimistic.
Figure 3. Scatterplots of Rainfall and Somali Deyr Crop Production
Per Capita Sorghum+Maize Production
According to United Nation estimates, Somalia’s population has doubled since 1995, while Deyr crop production totals have not increased. Figure 4 shows per capita Deyr Maize+Sorghum production estimates (i.e. crop production per person). In the last 10-12 years, approximately half of the Deyr seasons were associated with very low per capita crop production outcomes. 2018 appears likely to be another such season, with per capita maize+sorghum production of around 5.4 kg per person.
Figure 4. Deyr Per Capita Sorghum+Maize Production
Concerns About Pasture Conditions
Next, we turn to an assessment of pastoral conditions, focusing on the same three regions (Bay, Lower Shabelle and Middle Shabelle). This analysis is not meant to be an exhaustive assessment of rangeland conditions for the entire country. Furthermore, rangeland conditions may be more variable than crop outcomes, since grasses can respond quickly to late-season rains. However, through the first dekad of November (Figure 5) vegetation conditions (as represented by the USGS eMODIS NDVI) appear quite low. Vegetation greenness in these regions typically peaks in the last dekad of November.
Vegetation conditions exhibit persistence, and robust lagged relationships with prior rainfall totals. Hence, the end-of-November values can be predicted very accurately based on 1st dekad of November values and October 1-November 20 rainfall estimates (R2 values of ~0.8). Times series of the observed and predicted regional NDVI are shown in Figure 6. According to these estimates, peak NDVI in these regions appears substantially below normal and similar to previous severe drought years. Note also the sequence of repeated low Deyr NDVI values. The 2016, 2017, and 2018 values are all quite low – indicating repetitive shocks. The 2017 season March-May Gu season was poor, while the 2018 Gu season was normal-to-above normal. So, four out of the last five seasons seem to have been associated with poor growing conditions: Deyr 2016, Gu 2017, Deyr 2017, and Deyr 2018.
Figure 5. Regional eMODIS NDVI time series. The red lines depict the median values for the 2003-2017 period. The blue line shows 2018 conditions.
Figure 6. Time series of November dekad 3 eMODIS NDVI, along with predictions based on dekad 1 NDVI and October-November rainfall
Conclusions and Context
The most effective drought early warnings systems rely on multiple indicators, transitioning from climate forecasts and analogs before the onset of a rainy season, to mid-season projections of likely food system disruptions. Here, we have used FEWS NET monitoring tools to focus on mid-season projections for Somalia. While these projections should not be mistaken for assessments, our analysis has shown that for Somalia, a high level of predictability can be obtained in mid-November. This skill rests on the short duration of the Deyr growing season, the general aridity of the region, and the persistent nature of vegetation, soil moisture, and crop conditions. Unfortunately, the results presented also suggest another poor crop-growing season for Somalia. For the Bay and Shabelle regions analyzed, poor vegetation conditions also appear likely – conditions which could quite likely persist until the March-May Gu rains of 2019. While not examined in great detail here, precipitation totals and WRSI (Figure 1 and 2) also appear quite poor over Kenya, and poor Kenyan short rainy season harvest could be problematic, ultimately contributing to regional food and price stresses. Please note that it is probable that the marginal agricultural areas of the southeastern lowlands are likely to be more adversely affected by the current delayed onset, the quality of the seasonal rains, and the substantially reduced growing period.
The results concerning the Deyr harvest expressed here should be placed in the context of a good 2018 Gu harvest. Figure 7 below, taken from the 2018 post-Gu FSNAU-FEWS NET joint assessment (here), shows that the 2018 Sorghum+Millet Gu harvest was estimated to be about 147 thousand metric tons, the best harvest since 2010. On average, the Gu and Deyr harvests similar in magnitude, about 90 thousand metric tons, so the good Gu harvest will certainly help partially offset the poor 2018 cropping season. Current maize and sorghum prices are much lower than their peak in 2017, but historically prices also typically increase between December and April-May. It should also be noted, however, that the 2016 and 2017 Gu harvests were below normal, as were the 2016 and 2017 Deyr season harvests.
- Rainfall-based early assessments of the 2018 Deyr harvest indicate substantial (40-50%) deficits with little chance of recovery.
- Vegetation conditions in some areas are also quite poor, and predicted to remain so unless unseasonal rains arrive.
- While the 2018 Gu season was very good, Somalia also faces the stress of repetitive shocks in four of the past five rainy seasons, compounded by increasing population stress.
Figure 7. Gu Season Cereal Production – figure taken from the 2018 post-Gu FSNAU-FEWS NET joint assessment