On the relative role of climate change and management in the current desert locust outbreak in East Africa

HAL Id: hal-02747701

https://hal.inrae.fr/hal-02747701

Submitted on 3 Jun 2020

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Distributed under a Creative Commons Attribution - NonCommercial| 4.0 International

License

On the relative role of climate change and management

in the current desert locust outbreak in East Africa

Christine Meynard, Michel Lecoq, Marie-pierre Chapuis, Cyril Piou

To cite this version:

Christine Meynard, Michel Lecoq, Marie-pierre Chapuis, Cyril Piou. On the relative role of climate

change and management in the current desert locust outbreak in East Africa. Global Change Biology,

Wiley, In press, pp.1-3. �10.1111/gcb.15137�. �hal-02747701�

Glob Change Biol. 2020;00:1–3. wileyonlinelibrary.com/journal/gcb © 2020 John Wiley & Sons Ltd 

|

|

|

DOI: 10.1111/gcb.15137

L E T T E R T O T H E E D I T O R

On the relative role of climate change and management in the

current desert locust outbreak in East Africa

The current outbreak of the desert locust has affected much of eastern Africa and has reached as far as Pakistan and India in Asia, generating significant agricultural losses in a region that is already highly unstable economically, politically and in terms of food secu-rity for its human populations (FAO, 2020).

Desert locust outbreaks require a combination of weather, soil and vegetation conditions that favour the reproduction and aggregation of otherwise solitary individuals (Despland, Collett, & Simpson, 2000; Figure 1a). When those conditions appear, locusts aggregate, multiply in large numbers and migrate long distances, turning into a plague and devastating crops on their way. Solitary populations, which act as reservoirs for the gregarious forms, are likely to shrink their distribution under climate change because of a decrease in moisture and increased temperatures in much of the current recession range (Meynard et al., 2017). However, climate change could also expand part of this range at the margins, which includes some of the historical outbreak areas (Figure 1a; Meynard et al., 2017). Most importantly, outbreaks can start in very limited areas, from where swarms can travel thousands of kilometres. Therefore, a general shrinkage of the recession range does not nec-essarily translate into a decrease in the risk of outbreaks and plagues. As the waxing and waning of the monsoon rules the North African weather, rainfall, a major contributor to outbreaks, is erratic and difficult to forecast. Climate change scenarios include intensifi-cation of extreme weather events that could favour swarm forma-tion in some outbreak areas. For example, in spite of a significant long-term trend of increased incidence of drought in Africa (Thomas & Nigam, 2018), formation of swarms in 2018 was favoured by heavy rains caused by two tropical cyclones in the Arabian Peninsula. These extreme weather events allowed three generations of des-ert locusts to develop and go undetected until they spilled over into a much wider region (FAO, 2020). For these weather conditions to translate into agricultural risk, rainfall must be combined with fa-vourable vegetation and soil conditions, which may themselves re-sult from an interaction between climate and vegetation but also relates to human-induced change in land use (e.g. agriculture, wood extraction, urbanization), for which we do not have reliable fore-casts. Mechanistic models, which include the transition from soli-tary to gregarious forms in interaction with climate, vegetation and soil, are therefore urgently needed to accurately project the risk for desert locust outbreaks under climate change scenarios.

Beyond global change drivers, it is important to remember the long record of desert locust outbreaks, along with their management

success during the second half of the last century (Sword, Lecoq, & Simpson, 2010). Weather conditions that favour the development of swarms have been a constant threat to agriculture in the region for millennia (Waloff, 1966), and the climatic events observed since 2018 fall within the historical range (Abram et al., 2020). During the 20th century, research and international cooperation resulted, under the aegis of the Food and Agriculture Organization (Lecoq, 2003), in a concerted management effort based on identifying local hotspots where favourable conditions occur (e.g. Piou et al., 2019), to control potential swarm formation before they transform into a large-scale unmanageable threat (Figure 1a). This approach resulted in a consid-erable decrease in the number and intensity of locust outbreaks and plagues (Figure 1b). A key condition to the success of this manage-ment strategy, however, is the on-the-ground work that needs to be done in a sustained manner: active monitoring, information sharing between countries, preparation of the logistics for efficient control, maintenance of expertise over time, availability of emergency funds and crisis management plans. Detecting and controlling early stages of the swarm formation is therefore the most important step in this otherwise successful preventive strategy (Magor, Ceccato, Dobson, Pender, & Ritchie, 2005).

So, why did this particular outbreak wreak havoc and affect such a large area? We believe the answer lies mostly in socio-political instability. Since 2015, various countries in the Middle East and eastern Africa have been involved in armed conflicts or suffered from permanent insecurity. Some of the countries involved were therefore unable to sustain an expertise and monitoring effort that is perceived as only sporadically needed (Gay, Lecoq, & Piou, 2018). The early stages of swarm formation therefore went unchecked until the swarms had already turned into a plague (FAO, 2019).

The conditions that allowed this outbreak to expand as a plague and acquire such dangerous proportions can be compared to the cur-rent COVID-19 pandemic crisis. These have a synergistic effect with growing human densities and climate change effects on productive systems and human health. They both require a concerted moni-toring and on-the-ground control effort across borders, along with resources, expertise and infrastructure to support those actions. Moreover, these efforts must be kept in place over the long term to build resilience, despite the apparent lack of imminent threats (Gay et al., 2018). The lack of such a coordinated and sustained effort is likely to put human populations in many developing nations at dangerously higher risk. However, this also gives us hope in that the scientific knowledge that is required to manage those outbreaks at

2 

|

the onset has already shown its worth. Reinforcing early detection systems to prevent large-scale outbreaks is made even more critical by climate change, which may lead to more common propitious con-ditions in some of the outbreak areas. Our highest priorities should therefore be (a) to ensure that the political and socio-economic con-ditions are in place so that vulnerable human populations can adapt to new large-scale threats and (b) to maintain a culture of long-term risk assessment with constant necessary means.

Christine N. Meynard1

Michel Lecoq1,2

Marie-Pierre Chapuis1,2

Cyril Piou1,2

1_{CBGP, Univ Montpellier, CIRAD, INRAE, Institut Agro, IRD,}

Montpellier, France

2_{CIRAD, UMR CBGP, Montpellier, France}

Correspondence

Christine N. Meynard, CBGP, 755 Avenue du Campus Agropolis, CS 30016, 34988 Montferrier-sur-Lez cedex, France.

Email: christine.meynard@inrae.fr

F I G U R E 1   Possible states of desert locust populations with their transition drivers and distribution (a) and the historical occurrence

of plagues and recession periods (b). (a) Grey rectangles indicate management actions at each state; blue text indicates conditions for the transition from one state to the next. Global change, including land use and climate change, is most likely to affect conditions that promote the transition from solitary to gregarious populations (1)→(2). For example, although climate change scenarios point to an increase in aridity and further desertification in vast areas of Africa, some regions that have been at the origin of past outbreaks are likely to see a reversed trend (i.e. increase in frequency and intensity of rains). Vegetation is likely to respond to these changes, although the interaction between climate change, soil conditions, vegetation and human-driven land use change might be complex. Further studies are needed to anticipate the potential result of these interactions with respect to desert locust outbreak risk in the future. (b) Recent history of the desert locust situation (updated from Sword et al. (2010) with the most recent data from FAO until March 2020). The figure shows the number of countries reporting swarms for the period 1910–2020. Between 1910 and 1963, there was an onset or full plague event in 41 out of 53 years, whereas between 1964 and 2020 there have only been 8 years (out of 56 years) with smaller plague events. In 2019, and up to 1 April 2020, there were 15 and 18 countries, respectively, that had reported swarms

|

ORCID

Christine N. Meynard https://orcid.org/0000-0002-5983-6289

Michel Lecoq https://orcid.org/0000-0003-4515-3505

Marie-Pierre Chapuis https://orcid.org/0000-0003-4405-7722

Cyril Piou https://orcid.org/0000-0002-9378-9404

REFERENCES

Abram, N. J., Wright, N. M., Ellis, B., Dixon, B. C., Wurtzel, J. B., England, M. H., … Heslop, D. (2020). Coupling of Indo-Pacific climate variabil-ity over the last millennium. Nature, 579(7799), 385–392. https://doi. org/10.1038/s4158 6-020-2084-4

Despland, E., Collett, M., & Simpson, S. J. (2000). Small-scale pro-cesses in desert locust swarm formation: How vegetation pat-terns influence gregarization. Oikos, 88(3), 652–662. https://doi. org/10.1034/j.1600-0706.2000.880322.x

FAO. (2019). Locust watch, Food and Agricultural Organization of the United Nations. Desert Locust Bulletin, 483, 1–8.

FAO. (2020). Desert locust. Rome: Author. Retrieved from http://www. fao.org/locus ts/en/

Gay, P.-E., Lecoq, M., & Piou, C. (2018). Improving preventive locust management: Insights from a multi-agent model. Pest Management Science, 74(1), 46–58. https://doi.org/10.1002/ps.4648

Lecoq, M. (2003). Desert locust threat to agricultural development and food security and FAO/International role in its control. Arab Journal of Plant Protection, 21, 188–193.

Magor, J. I., Ceccato, P., Dobson, H. M., Pender, J., & Ritchie, L. (2005). Preparedness to prevent desert locust plagues in the Central region, an historical review. Report no. AGP/DL/DS/35; Desert Locust Technical Series. Food and Agriculture Organisation.

Meynard, C. N., Gay, P.-E., Lecoq, M., Foucart, A., Piou, C., & Chapuis, M.-P. (2017). Climate-driven geographic distribution of the desert locust during periods: Subspecies’ niche differentiation and relative risks under scenarios of climate change. Global Change Biology, 23(11), 4739–4749. https://doi.org/10.1111/gcb.13739

Piou, C., Gay, P.-E., Benahi, A. S., Ebbe, M. A. O. B., Chihrane, J., Ghaout, S., … Escorihuela, M.-J. (2019). Soil moisture from remote sensing to forecast desert locust presence. Journal of Applied Ecology, 56(4), 966–975. https://doi.org/10.1111/1365-2664.13323

Sword, G. A., Lecoq, M., & Simpson, S. J. (2010). Phase polyphenism and preventative locust management. Journal of Insect Physiology, 56, 949–957. https://doi.org/10.1016/j.jinsp hys.2010.05.005

Thomas, N., & Nigam, S. (2018). Twentieth-century climate change over Africa: Seasonal hydroclimate trends and Sahara desert expansion. Journal of Climate, 31(9), 3349–3370. https://doi.org/10.1175/JCLI-D-17-0187.1 Waloff, Z. (1966). The upsurges and recessions of the desert locust