Very poor pasture conditions likely to persist through early spring

Chris Funk

This is yet another post about the low short/Deyr rains in East Africa, but today’s focus is on the very poor pastoral conditions in southeastern Ethiopia, northeastern Kenya, and Somalia. This blog is motivated by the extremely low NDVI values, discussed in a recent alert by FEWS NET as well as an email from my friend John McGrath at OXFAM who forwarded me an email from his colleague James Firebrace, who is reporting some severe outbreaks of acute malnutrition and water shortages in eastern Somaliland. After analyzing the available remote sensing data, I find such reports plausible, given the cumulative January-November NDVI record, and would suggest we pay very close attention to food security conditions in this area.

I was already planning to write this post when I arrived at work this morning, before I read John’s email. My concerns were motivated by the very large observed NDVI anomalies combined with the fact that the full impact of the October/November dryness may not be fully registered by the current vegetation.  There is a large degree of persistence and predictability in the NDVI record, and we wrote a paper on this back in 2006 that included a target application on exactly the region under stress now. NDVI tends to lag behind rainfall, so the current poor rainfall could lead to further drying. Even without more drying, it is unlikely (but possible) that the region will see much relief until spring 2017.

Figure 1 shows the most recent MODIS land surface temperature and NDVI anomalies. Many pastoral areas are very warm, which may indicate low levels of soil moisture, and satellite-observed vegetation levels are near or below historic lows in many areas.

 

Figure 1. MODIS Land Surface Temperature and NDVI anomalies for the 1st dekad of November 2016.
Figure 1. MODIS Land Surface Temperature and NDVI anomalies for the 1st dekad of November 2016.

These conditions appear related to long term persistent dryness in the region, as indicated by Standardized Precipitation Index values for the last dekad, month, 2 months, 3 months and 6 months (Figure 2).

Figure 2. Standardized Precipitation Index values calculated from the 1st dekad of November 2016. From earlywarning.usgs.gov.
Figure 2. Standardized Precipitation Index values calculated from the 1st dekad of November 2016. From earlywarning.usgs.gov.

Convergent evidence for water stress and poor water availability for cattle, goats and camels is provided by the FEWS NET waterpoint viewer. Figure 3 shows the current assessment – much of northeastern Kenya and southeastern Ethiopia is under alert or near-dry conditions.

Figure 3. USGS Waterpoint conditions as of early November 2016.

Figure 3. USGS Waterpoint conditions as of early November 2016.

We can look at stressed regions using time series of MODIS Normalized Difference Vegetation Index (NDVI) data. MODIS NDVI measures vegetative health at very high resolution (250m). Figure 4 shows time series of NDVI from far eastern Ethiopia. One year, 2003, was less green. Two recent very poor years 2009/2010 and 2010/2011 were actually greener. By early November, most years have already reached or passed the maximum NDVI value. Typical behavior is for the vegetation to senesce and dry from this point forward.

Figure 4. Somaliland NDVI time series.
Figure 4. Somaliland NDVI time series.

Figures 4, 3, 2 and 1 provide convergent evidence support John McGrath’s concern about very dry conditions in far eastern Ethiopia. This year looks way drier than most recent years.  In terms of long term moisture stress and poor pastoral conditions, it is very concerning that both January-to-early November NOAA CPC RFE2 rainfall totals and January-to-early November NDVI averages indicate very poor conditions (Figure 5). I am not an expert on pastoral early warning, but I believe this kind of repeated aridity can weaken herds and reduce their milk production.

Figure 5. Scatterplot showing 2003-2016 Jan-Nov RFE2 rainfall totals and average eMODIS NDVI for Somaliland.
Figure 5. Scatterplot showing 2003-2016 Jan-Nov RFE2 rainfall totals and average eMODIS NDVI for Somaliland.

Focusing on the same type of target – the anticipated average NDVI conditions between the second dekad of November and the last dekad of March, we find that simple regressions between the Jan-Nov1 NDVI (as shown in Figure 5) and Nov2-March NDVI have a reasonable R2 (~0.4). We can use this simple regression to project a plausible ‘what-if’ scenario for the rest of the dry season. This result is shown in Figure 6.

Figure 6. Somaliland NDVI projections.
Figure 6. Somaliland NDVI projections.

What this figure is telling us is that its quite likely that unless an unseasonal storm drops a lot of water in Somaliland, further browning of the vegetation is likely, as we saw in 2009/2010 and 2010/11. These seasons also appear to be the closest analogs, based on our projected Nov 2016-March 2017 ‘forecast’.

We next carry out a similar analysis for the Mandera region of NE Kenya (Figure 7). Once again, we see historically low levels of NDVI, drier than in 2010. Here, we do seem to be earlier in the season, and there seem to be more years that had a late December recovery.

Figure 7. NDVI time series for the Mandera region of NE Kenya.
Figure 7. NDVI time series for the Mandera region of NE Kenya.

Applying our same ‘forecast’ strategy, i.e. predicting Nov 2016-March 2017 NDVI based on January-November 2016 NDVI (R2=0.4), gives us the results shown in Figure 8. Here the forecast is more modest – a simple continuance of current historic low levels. The analog years based on this analysis might be 2005/2006 and 2010/2011. The USGS waterpoint analysis (Figure 3) provides a strong level of convergence on dryness in this area, and barring an unseasonal upturn in the rains, which has happened before, poor pastoral conditions seem likely to continue, based on the data analyzed here.

Figure 8. Projection of Nov 2016-March 2017 NDVI for Mandera.
Figure 8. Projection of Nov 2016-March 2017 NDVI for Mandera.

We conclude by presenting a new experimental Potential EvapoTranspiration (PET)  forecast, produced by Daniel McEvoy (DRI) and Shrad Shukla (CHG). This forecast (Figure 9) shows the median CFSv2 ensemble forecast over East Africa. The CFSv2 is a sophisticated coupled ocean-atmosphere model used for seasonal forecasts. The total number of ensemble members is 28. They were initialized at an interval of 5 days starting October 8th, 2016 through November 7, 2016.  According to this figure the PET outlook appears to be mostly within normal range (standardized anomaly of -0.44 to 0.44) over the drought regions (Kenya and Somalia).

Figure 9. PET forecasts for Eastern Africa. Kindly provided by Daniel McEvoy (DRI) and Shrad Shukla (CHG).
Figure 9. PET forecasts for Eastern Africa. Kindly provided by Daniel McEvoy (DRI) and Shrad Shukla (CHG).

Putting this all together, we can say that there is lots of evidence that pastoral areas in eastern Ethiopia, NE Kenya, and Somalia appear to have experienced very low rainfall, and that this has resulted in very low NDVI values, both at present and over the January-November time frame (Fig. 6, 8). The poor pasture conditions associated with these low NDVI values appears associated with very warm air temperatures (Figure 1) and water point estimates that appear to be almost dry in many places (Figure 3). The cumulative low NDVI values of the current Jan-Nov season appear to be very low, likely to persist, and similar to seasons like 2009/2010 and 2010/2011.  PET forecasts appear normal, but normal behavior for this region is associated with senescence and NDVI declines in most cases.

Setting aside the outlook for spring 2017 rains, we can look at FEWS NET assessments from January of 2010 and 2011 as possible indicators of where we might be in a few months (a, b, c). We at the CHG are not qualified to do food security assessments, but it does seem safe to say that the current pastoral conditions are very poor in many places, and unlikely to improve until spring. This may mean continued reductions in herd health and pastoral livelihoods. Close monitoring and assessment seems warranted.

 

 

A very poor East African short rains seems almost certain

Chris Funk

 

Last month on this blog we predicted a poor short rainy season for Eastern Kenya and Southern Somalia. Unfortunately that forecast verified. Strong cool-warm-cool sea surface temperature contrasts across the cool Western Indian Ocean, warm Eastern Indian/Western Pacific, and cool Eastern Indian oceans conspire to produce a very strong precipitation dipole (Figure 1) contrasting very heavy precipitation over the Indo-Pacific Warm Pool to the east and the Western Indian Ocean and East Africa to the west. USGS crop and rangeland models indicate ‘no start’ to the growing season almost everywhere.

Figure 1. October 2016 CHIRP rainfall anomalies
Figure 1. October 2016 CHIRP rainfall anomalies

This is very concerning given that the short rains typically end in November for most places in Eastern Kenya and Southern Somalia in November. There is also a great deal of persistence in the climate system between October and November-December. Thus the correlation between October and October-November-December (OND) E. Kenya/S. Somalia rains (please see last post for the specific region) is extremely high: 0.91. Despite that, the mean of the OND rains (224 mm) is much greater than the mean for October (64 mm) (Figure 2).

Figure 2. Scatterplot showing the strong relationship between October and OND E. Kenya/S. Somalia rains.
Figure 2. Scatterplot showing the strong relationship between October and OND E. Kenya/S. Somalia rains.

This is really a quite stunning predictive relationship. November-December E. Kenya/S. Somalia rains also have a strong correlation with October sea surface temperatures (Figure 3). These correlations are really high, with a negative relationship to the Indo-Pacific Warm Pool of -0.9, and positive relationships to the Western Indian and Eastern Pacific of +0.5 and +0.7.

Figure 3. Correlation between November-December E E Kenya/S Somalia rainfall and November-December sea surface temperatures.
Figure 3. Correlation between November-December E E Kenya/S Somalia rainfall and November-December sea surface temperatures. Based on data from 1996-2015.

Unfortunately, the current (October) Ocean looks very much like the opposite of Figure 3 – warm in the Indo-Pacific Warm Pool and cool in the Eastern Pacific (Figure 4). The warmth in the West Pacific is quite exceptional >+2.5 standardized anomalies, which is equivalent to a very warm 30.3 Celsius.

Figure 4. Observed October 2016 sea surface temperatures expressed as standardized anomalies. Based on a 1981-2010 baseline and NOAA Extended Reconstruction v4 data.
Figure 4. Observed October 2016 sea surface temperatures expressed as standardized anomalies. Based on a 1981-2010 baseline and NOAA Extended Reconstruction v4 data.

These strong SST gradients and warm Western Pacific sea surface temperatures contributed to the strong Precipitation dipole (Figure 1) and dry East African conditions in October. At this point, as shown in a recent Africa Hazards Briefing by Nick Novella at NOAA’s Climate Prediction Center (Figure 5), rainfall is very low and recovery is very unlikely. Nick’s awesome Seasonal Performance Probability Tool uses the long historical record of the ARC2 dataset to explore the potential future outcome of a season at a given time and place. It is not looking good for Eastern Africa.

Figure 5. Past rainfall performance and potential future rainfall performance at Baidoa, Somalia. Each grey line represents a projection based on a previous year of the ARC2 data set.
Figure 5. Past rainfall performance and potential future rainfall performance at Baidoa, Somalia. Each grey line represents a projection based on a previous year of the ARC2 data set.

We next explore this issue using two separate approaches: analog seasons and formal (but simple) cross-validated forecasts of OND rainfall. Our composites are based on similar dry Octobers (Figure 6)  1996, 1998, 2005, and 2010 exhibited similar very low October rains.

Figure 6. 1981-2016 CHIRPS E Kenya/S. Somalia rainfall and analog years.
Figure 6. 1981-2016 CHIRPS E Kenya/S. Somalia rainfall and analog years.

What is interesting about these years is that they also tended to exhibit a strong gradient between the Indo-Pacific Warm Pool and Eastern Pacific Ocean (Figure 7). The Western Indian Ocean and the associated Indian Ocean dipole likely played a role as well, but is not explored here, since recent correlations with E Kenya/S Somali rains seems quite low (Figure 3).

Fig. 7. Indo-Pacific warm pool and Eastern Pacific sea surface temperatures from the boxes identified in Figure 5. Dry October analogs are shown with filled black circles.
Figure 7. Indo-Pacific warm pool and Eastern Pacific sea surface temperatures from the boxes identified in Figure 5. Dry October analogs are shown with filled black circles.

Note that the selection of analog years was based on just dry Octobers, so finding our analogs clustered in Figure 7 helps reinforce the strong sea surface temperature forcing indicated in Figure 3, which in turn helps explain the strong Oct-OND relationship indicated in Figure 2. When I used the excellent GeoCLIM tool to plot rainfall anomalies for these analog seasons (Figure 8) I found that these analogs would indicate very poor rainfall performance in Kenya and Somalia, and a poor performance of the Deyr rains in Ethiopia. The 2016 March-April-May rains were very poor in Kenya and Ethiopia. Southeastern-Central Ethiopia is extremely food insecure, having experienced substantial droughts or dryness in the past two Belg and past two Kiremt rainy seasons.

Figure 8. Analog CHIRPS anomalies, expressed as percentages.
Figure 8. Analog CHIRPS anomalies, expressed as percentages.

The prospect of a poor E. Kenya/S. Somalia season can be quantified formally via a simple cross-validated regression using October CHIRPS observations (Figure 2) and Indo-Pacific and East Pacific sea surface temperatures (Figure 7). I first predicted November-December precipitation and then added in the observed October values. The forecast (Figure 8) predicted 1996-2015 OND rains very well (cross-validated R2 of 0.8) and projects an expected OND total of 83 mm, with a standard error of +/- 53 mm. So it seems very likely that the season will be very poor.

This poor season will follow a very poor 2016 MAM rainy season. I made a MAM+OND ‘forecast’ by combining the observed MAM and October E. Kenya/S. Somalia values with our November-December forecasts (Figure 9). The story that emerges is that this region may experience the worst MAM+OND rains in the past 20 years. Since we can be almost certain that short rains outcomes are going to be poor, especially for farmers in Eastern Kenya and Southern Somalia, it may be possible to engage in proactive response planning. While pasture conditions can change more rapidly if anomalous late season rains arrive, current  estimates of vegetation health look quite low.

Figure 9. Cross-validated forecasts of E Kenya/S Somalia MAM+OND 2016 rains.
Figure 9. Cross-validated forecasts of E Kenya/S Somalia MAM+OND 2016 rains.

FEWS NET continues to develop new tools for monitoring and modeling drought.  For example, support from NASA SERVIR is enabling us to provide CHIRPS-compatible Global Ensemble Forecast Systems (GEFS) forecasts, which can be viewed on our Early Warning eXplorer.  Collaboration with the Desert Research Institute has created the FEWS Engine which leverages the incredible processing power of the Google Earth Engine (GEE). We can use the GEE to produce NDVI composites for our analog years (Figure 10) reinforcing our concerns.

Figure 10. Google Earth Engine composites of OND MODIS NDVI for 2005 and 2010.
Figure 10. Google Earth Engine composites of OND MODIS NDVI for 2005 and 2010.

All indicators converge on a very high probability of a very poor short rains. Looming on the horizon is the potential of La Nina-like conditions in the spring. While current NOAA CPC assessments indicate that this is unlikely, if a La Nina did arrive, and the West Pacific continued to be very warm, we might see another poor season in the spring of 2017. If so, providing an adequate response to a 2016 short rains drought would help increase East African resilience in 2017.