Physical Characteristics of Sub-Saharan Africa

Hello all!

Previously, I spoke about Sub-Saharan Africa and how it has been met with ecosystem degradation due to an undervaluation of ecosystem services. In this post, I will touch on the general physical characteristics of Sub-Saharan Africa, which will subsequently help us to understand the distribution of water as an ecosystem function within the region.

Physical Characteristics

Sub-Saharan Africa, as a whole, encompasses a massive land area of about 24 million km² (Hammond and Antwi, 2010); the SPUs including lakes, wetlands, rivers and reservoirs span 6% of the continental area of Sub-Saharan Africa with an overall area of 1,448,771 km² (Rebelo et al. 2010). This area is marked by large spatial heterogeneity: 66% of the land area is characterised by arid and desert conditions, and only 26.9% of the total land area is viable arable land for livestock cultivation and food production (Cotula et al. 2009). The disparity in natural conditions is largely explained by the large variability in climatic conditions, which is controlled by global patterns of atmospheric circulation (Taylor, 2004).

Quintessentially, the Hadley cell controls most of Africa's atmospheric circulation. Around the world, a low pressure belt forms where insolation is concentrated at the equator, rises and flows towards the polar regions. As this air flows poleward, it cools and descends at latitudes of approximately 30°N and 30°S forming a high-pressure belt with stable air conditions and little moisture. Subsequently, the subsiding air at these latitudes either head poleward or equatorward to complete the Hadley cell. Due to the Earth's rotation, the Coriolis force comes into play and these equatorward air movements are deflected clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere to form the northeasterly and southeasterly trade winds respectively. They converge to form the Inter-tropical Convergence Zone (ITCZ), where the convective and convergent uplift bring a large amount of rainfall to the region within the ITCZ as seen in Figure 2.

Figure 2. a) January and b) August. The migration of the ITCZ (red band) over the course of the year creates great seasonality over the African continent, bringing most rainfall to Central Africa in August and most rainfall to South Africa in January. Picture from Ziegler et al. (2013)

Due to Africa spanning across equatorial and subtropical latitudes and the movement of the ITCZ, the mean annual rainfall is characterised by marked spatial variability, ranging between 100mm at the Sahel regions and 1500mm at the coast of West Africa (Eltahir and Gong, 1996). Concomitantly, such diverse climatic conditions deliver different distributions of Ecosystem Service Providing Units (SPU) throughout Sub-Saharan Africa, and within countries their dependency on types of ecosystem services varies as physical conditions change (Egoh et al. 2012). In the wetter regions of western and central Africa, agricultural produce of food and benefits from raw materials are more important ecosystem services; in the arid and semi-arid countries of southern and northern Africa, tourism, grazing and water are of greater priorities.

The important role of water resources delivering ecosystem services within Sub-Saharan Africa will be elaborated more in the next post, where I will be looking at the water bodies in greater specificity.

See you next week!

State of Sub-Saharan Africa

Hello all!

In my previous post, I have briefly talked about what ecosystem services are, and the role of water in ecosystem functions. In this post, I will talk further about the relationship between water and ecosystem services contextualised in Sub-Saharan Africa, and why we should use an ecosystem services framework for decision-making in the pursuit of development.

Sub-Saharan Africa

In the literature, Sub-Saharan Africa has been facing a high incidence of ecosystem degradation in from urbanisation, comparable to that of the 19th century industrial revolution in Europe (Wangai et al. 2016).  Demand on ecosystem functions (eg. water for consumption, wood for timber) have exceeded that of supply, and this has diminished the supplies of ecosystem services through the overexploitation and fragmentation of ecosystems (Cumming et al. 2014). Current population growth of Sub-Saharan Africa at 2.7% is likely to continue inducing pressure on water resources and initiate large-scale water resource schemes in response to human needs, which may further threaten water availability (World Bank, 2017) - within urban East Africa, the 30 years elapsed between 1967 and 1997 have already seen a dramatic decline in mean per capita water use in all urban households from 98.7L to 54.9L per day (Thompson et al. 2000). There was also a tripling of average time spent collecting water for households without piped supplies, resulting from reasons such as over-strain on municipal water supplies due to urban overpopulation.

A continued desire to exploit the scarce resources for use may result in: a) resource conflicts, such as for countries along the River Nile and Okavango Delta (Hobbs, 2004) and b) continued degradation and losses of vulnerable water bodies such as wetlands. Climate change has been predicted to cause further desertification within Sub-Saharan Africa (Wangai et al. 2013), and hence it is essential to to ensure for a continued supply of ecosystem services to sustain livelihoods and safeguard agricultural productivity in our pursuit of development.

So far, ecosystem functions have been considered a "public good" where there is no excludability or rivalry from accessing an ecosystem good (Wangai et al. 2016: 227), and the abovementioned incidences of ecosystem degradation in Sub-Saharan Africa arguably stems from this undervaluation of ecosystem services in conventional policy-making (Potschin et al. 2016). Valuation of water as an ecosystem service is therefore an appealing approach to the management of water resources and establish conservation strategies for the future. In particular, the ecosystem services approach encompasses identifying, measuring, modelling the stocks and flows of ecosystems, and the synergies or trade-offs that occur from decision-making. Although this may sound unclear at present, I will elaborate more on these ideas in the following posts through the following themes:

1. Identification of ecosystem service functions and delivery in Sub-Saharan Africa, and the differences within.

2. Application of ecosystem services approach and valuation of water in Sub-Saharan Africa through measurement of ecosystem services.
3. Modelling ecosystem services for the future (eg. threat of climate change, how to include them in conservation strategies).

4. Limitations of the ecosystem services approach in the current literature, and trade-offs that may occur in decisions.

These area of interests are likely to change as I progress in my knowledge around this topic. Having also read through the past year examples (1, 2, 3), I will try my best to minimise content overlap, and ideally further my seniors’ ideas and frameworks for a more comprehensive understanding of this topic.

See you next week!

Ecosystem Services: Why and What

Hello all!

Having enrolled in the ‘Water and Development in Africa’ module, I have chosen to examine the relationship between water resources and the provision of ecosystem services. My choice stemmed from my module preferences in the previous academic year: a) Ecological Patterns and Processes, b) Surface and Groundwater Hydrology, and c) Development Geography. The premise of water being considered an ecosystem service therefore stood out to me as an effective way to consolidate my knowledge from these three different subject areas of Geography. In this post, I will briefly talk about  the role of water within ecosystem functions, and provide a framework which may help for future posts.

Water: The Heart of Life

Figure 1. Basic ecosystem services/functions arising from water (Van Leeuwen et al. 2012).

Ecosystem services can briefly be defined as “the benefits human populations derive, directly or indirectly, from ecosystem functions" (Costanza et al. 1997). Water lies at the heart of many of these ecosystem functions, evident from Figure 1 - water is a necessity to the survival needs of human population, to the maintenance of biodiversity (eg. habitat for fish, for human consumption and livelihoods), and to the maintenance of forests for timbre and wood. Water has therefore also been cited as an "umbrella service" within the field of ecosystem functions, and that efforts to better manage and conserve water in watersheds indirectly help to preserve other ecosystem functions as explained earlier (Turpie et al. 2008: 789) .

The Common International Classification of Ecosystem Services has emerged as a framework to represent ecosystem services in the form of a hierarchy, classifying ecosystems services at the most general level in the familiar categories used in the Millenium Ecosystem Assesment (2005): provisioning, regulating, and cultural services. I have chosen the CICES as a framework in preference to the MEA due to the explicit quantification of benefits to human populations within the sub-categories; the CICES is also broader in its functions, including abiotic energy sources such as tidal energy (Turpie et al. 2017). I have extracted examples from the CICES Version 4.3 in relation to water resources in Table 1 as shown below (BISE, 2017)

Table 1. Selected sections of the Version 4.3 Common International Classification of Ecosystem Services (BISE, 2017).

Section	Division	Group	Class	Class Type
Provisioning	Nutrition	Water	Surface water for drinking	Eg. 100mm of surface water from rivers for drinking
			Groundwater for drinking	Eg. 240mm of freshwater from groundwater for drinking
	Materials	Water	Surface water for non-drinking purposes	Eg. 100mm of abstracted surface water from rivers for washing and cleaning.
			Groundwater for non-drinking purposes	Eg. 240mm of freshwater from groundwater for irrigation and livestock consumption.
Regulation and Maintenance	Mediation of waste, toxics and other nuisances	Mediation by ecosystems	Dilution by atmosphere, freshwater and marine ecosystems	Eg. Dilution of fluids and solid waste in lakes.
	Mediation of flows	Liquid flows	Hydrological cycle and water flow maintenance	Eg. Rainfall recharge into a 200m^3 river.
	Maintenance of physical, chemical and biological conditions	Water conditions	Chemical composition of freshwaters	Eg. Buffering of chemical composition of freshwater column by re-mineralisation of phosphorus.
			Chemical composition of salt waters	Eg. Buffering of chemical composition of seawater column and sediment for favourable living conditions (eg. denitrification).
Cultural	Physical and intellectual interactions with biota, ecosystems and landscapes.	Physical and experiential interactions	Experiential use of plants, animals and landscapes in different environments.	Eg. Snorkelling, diving.

In my next post, I will elaborate more on the academic motivations for studying the relationship between water and ecosystem functions, and hopefully contextualise within my regional area of interest: Sub-Saharan Africa.

See you next week!