El Niño, La Niña and rural livelihood
How does extreme climate variation due to events such as El Niño and La Niña impact rural livelihood in sub-Saharan Africa?
The two extreme phases of ENSO control climatic factors that regulate ecosystem net primary production (NPP). El Niño and La Niña impact rainfall in two ways; either by decreasing rainfall and extending dry seasons, or by increasing rainfall that causes floods and subsequent loss in agricultural productivity.
Hakim Abdi from the Department of Physical Geography and Ecosystem Science at Lund University and his colleagues published in the September issue of Climatic Change a study where they analyzed the impact of these climatic phenomena on NPP supply and demand during 2000 – 2013. They developed a methodology combining data from a NASA satellite sensor, socioeconomic data from the Food and Agriculture Organization of the United Nations, and climatic indices from NOAA to demonstrate the linkage between ecosystem productivity, human livelihood and climatic variability. NPP supply is the annual provision of crops, animal feed and pasture, and woody biomass, while demand is the human-driven consumption such as food, fuel and feed. The ratio of NPP supply and demand provides an approach of determining the social and ecological vulnerability of the continent.
The trend analysis of NPP supply shows it has been significantly changing in 32 % of sub-Saharan. Increases in NPP are concentrated to the western Sahel with an average NPP of 2 grams of carbon per meter square per year (g C m-2 yr-1) and central Africa (30 g C m-2 yr-1), while decreases in NPP were in parts of Zambia, Malawi and Mozambique (-25 g C m-2 yr-1). The changes in demand were significant over 48 % of sub-Saharan Africa, and calculated to be 3.5 grams of carbon per meter square per year on average. Increase in NPP demand has experienced a steep increase in twentieth century and is mainly concentrated to urban areas, where average demand was around 50 grams of carbon per meter square per year. For example, Addis Ababa’s population increased by 40 % between 2000 and 2010, and consequently the average trend in NPP demand there was one of the highest in the continent (153 g C m-2 yr-1).
The tradeoffs between NPP supply and demand trends (i.e. change in one quantity relative to another) are locally constrained and linked to the prevailing climate, population growth and net migration. It is also clear those favorable conditions, where supply exceeds that of demand, could be interpreted in various ways. Where the trend in NPP demand is low but the population is increasing could be an indication that the population is not consuming adequate amounts of food, feed and fuel. Also, it could point out that the crops cultured in the area are not used for nutrition nor for increasing the wealth of locals. In Sikasso in southern Mali, the NPP supply is 10 g C m-2 yr-1 while the demand is on average 1 g C m-2 yr-1. However, the main crop in the area is cotton, an important cash crop for the region, yet nutrition statistics show one fifth of the population suffers from chronic malnutrition.
Climatic Change, September 2016, Volume 138, Issue 1, pp 111–125