The Importance of the Ephemeral Kuiseb River as Linear Oasis. Its Ecosystem Services For Namibia

The importance of the ephemeral Kuiseb River as linear oa­sis and its provided ecosystem services (Namibia)

Philipp, Luca1

(1) Justus-Liebig-University GieBen, Germany

Abstract

Ephemeral rivers, such as the Kuiseb, are from tremendous importance for the dependent eco­systems, economies and people that rely on its water resources. It is part of aunique landscape, which has formed under extreme conditions. Highly specialized, often endemic species were able to emerge. The Topnaar (#Aonin) are an indigenous population living along the Kuiseb for centu­ries that has managed to practice agriculture in this very barren and hyper-aridlandscapemainly by cultivating native, endemic plants.To emphasize this, the Ecosystem services model (MA [Mil- lenium Ecosystem Assessment], 2005) was applied to identify and classify the ecosystem ser­vices offerd by the Kuiseb River. The study will also take a look at Namibias community-based natural resource management (CBNRM) which is one of the longest established payment for ecosystem services scheme of the world. Moreover, the Kuiseb Basin Management Committee (KBMC) will be considered which strives to provide efficient and equitable access to water and sustainable use of related resources in the Kuiseb River basin.

KEYWORDS: Africa, arid environmensts, conservation, desert, ecosystem services, ephemeral river,management, Namibia, riparian forest, water, vegetation

1. Introduction

A growing world population leads to a higher demand for food and water, more living space is needed and consumption is also increasing. Many people forget, or perhaps better said, displace the long-term problems that will be faced if we do not change our current habits. This myoptic behavior will lead to more problems in the future if no effective countermeasures are taken. Na­mibia was the first country to establish nature conservation as a constitutional goal. Not only in this area I see the country taking a pioneering role (example: communal nature conservation). We can also learn from Namibia in terms of sustainable management methods and the careful use of natural resources and their exploitation. The current forecasts of the Intergovernmental Panel on Climate Change (IPCC) clearly show the problems that can be expected in the future.

In adry-climate, often drought-stricken country like Namibia, the availability and access to water plays a major role for the persistence of natural ecosystems. Its water resources heavily rely on the rainfall. Precipitation shows a great variability, is unpredictable and only falls during the wet season creating temporary water pools, recharging the underground water and filling the rivers. The importance of water becomes clear, if you consider that the country has a water deficit. Meaning that the potential evaporation exceeds the precipitation which leads to very low moisture. Water supply and distribution to the coastal regions has always been a challenge. Perennial rivers only exist along the Northern and Southern border of the country. That's why ephemeral rivers, such as the Kuiseb, play an essential role in the supply of water and for the maintanence of ecosystems that rely on the accessability of water. The dynamics of riparian vegetation along the Kuiseb river is controlled by the cooperation of different influencing factors like the geology, sur­face hydrology, ecosystems and human use (Arnold et al., 2016; Benito et al., 2010). As an erratic flowing river plants and humans are susceptible to variations in the supply and use of water (Ar­nold et al., 2016).

The objective of this research is to highlight the importance of the ephemeral Kuiseb River with its natural resources and ecosystem services for the depending ecosystems, humans and econ- omies.Thus,an analysis referring to the ecosystem services model (MA [Millennium Ecosystem Assessment(Program)], 2005)was applied at the Kuiseb River. Furthermore, the significanceof community-based natural resource management and the role of a basin management committee were considered.

2. Study area

In the following, a description of the specific characteristics of the investigation area will be given for a better understanding of the landscape.

2.1 Location and Landscape

The Kuiseb river, located in west central Namibia, is a characteristic ephemeral river which can be described as endoreic because it rarely reaches the Atlantic Ocean at present (Ringrose et al., 2014). It is one of the 12 major westward flowing ephemeral rivers, and with a length of ap­proximately 560 km one of the longest in Namibia (Dahan et al., 2008). His origin lays in the Khomas Hochland (2347 m a.s.l.), passes down the Great Western Escarpment and flows through the Namib-Naukluft Park between the Namib Dunes in the south and the Central-western Plains in the north towards the Atlantic coast near Walvis Bay (Henschel, 2006). It represents a natural barrier for the sand dunes of the Namib to the South and divides it from the gravel plains in the North. His catchement covers 15.500 km2 and can be divided into upper, middle and lower catchment (Jacobsen et al., 1995) (Fig. 1).The vegetation ofthe upper basin is characterized by thorn treesavanna (Henschel, 2006). Along the middle reaches riparian vegetation and trees are most present. This part of the basin is located within the Namib-Naukluft National Park, where the focus lays on tourism, conservation, environmental work and research (ibid.). In the lower basin the river is divided into a couple of channels where it forms a delta and the Walvis Lagoon - a wetland of great importance for nature conservation and biodiversity belonging to the Ramsar sites (ibid.).

Abbildung in dieser Leseprobe nicht enthalten

Fig. 1: Location oft he Kuiseb River catchment, Botes et al. (2003).

2.2 Geology

On its way to the Atlantic Ocean the Kuiseb passes through different geological units. The whole catchment lays within the Damara Supergroup and Gariop Complex which mainly consits of schists. Belonging to the Precambrian and Cambrian formations these rocks deposited 850 to 500 million years ago. In the middle and lower catchment Damara granite intrusions (~570 mio. years) can be found as well as younger rocks from the Karoo sequence (~320 mio. to 200 mio. Years) (Jacobsen et al., 1995). The bordering Namib Dunes in the south are underlayed by the Kalahari Group (Fig. 2). In the last 4 to 2 million years the Kuiseb was able to cut into the under- layinng rocks and forming a deep canyon, which enables us to have a close look at the stratigra­phy today (Jacobsen et al., 1995).

Abbildung in dieser Leseprobe nicht enthalten

Fig.2: Geology of Namibia,Uni Koeln (2002).

2.3 Climate

Namibias climate is characterized by semi-arid to arid conditions with very limited water re­sources, providing a serious challenge in terms of water supply. According to Henschel (2006) it is the driest country in Sub-Saharan Africa.

Originating in the Khomas Hochland, the Kuiseb receives in his Upper catchment up to 350 mm of rainfall per year. On his way to the coast it flows through very arid regions (rainfall < 100 mm/a) and by reaching the coast the rainfall drops to almost zero. (Fig. 5) Rainfall within the catchment is decreasing towards the coast but the variability is increasing (Jacobsen et. al, 1995). The av­erage annual temperature within the Kuiseb catchment is quite variable due to various different landscapes and their topography. Close to the coast the temperatures can be less than 16 °C, caused by cold south-westerly winds, fogs and clouds as a result of the cold Benguela current (Mendelsohn et al., 2002). Temperatures increase to more than 22 °C towards the inland in the Namib-Naukluft Park and the Central-western plains and decrease again when reaching the Khomas Hochland in the upper reaches of the Kuiseb (ibid.) (Fig. 3). The evaporation shows the same pattern, which ranges between 1700-2300 mm/annum in the Kuiseb catchment (ibid.).

Abbildung in dieser Leseprobe nicht enthalten

2.4 Hydrology

Abbildung in dieser Leseprobe nicht enthalten

Fig. 4: Flowing Kuiseb River, Bethune (2020).

Due to Namibias‘ arid climate ephemeral rivers play an essential role in supporting Namibias people. As surface water is very limited they only flow for a short period after good rains in their catchments (Fig. 4). The runoff events in the Kuiseb are directly related to the precipitation events in the catchment area. Here, the intensity of pre­cipitation and the location of the precipitation fields are decisive. The precipitation can trigger flash floods. Runoff events are mainly formed in the eastern part of the catchment area and contribute to the replenishment of the groundwater reserves.

The Kuisebs‘ alluvial aquifer (~240 Mm3) gets recharged from erratic floods which have their source in the upper catchment.

Depending on the catchment the occurence of recharge is different:

- 11 out of 13 years in the middle catchment
- 11 out of 28 years in the middle-lower reaches(Benito et al., 2010).

Apart from the aquifer, another water source are various boreholes along the Kuiseb, especially in the lower and mid-lower catchment (Swartbank & Rooibank aquifer). In addion to that water abstraction facilities in Walvis Bay are necessary to meet the water demands in situations of high request, e.g. accommodation for tourists in the holiday season. The groundwaters are extremely important for the coastal region in the middle of Namibia, as the two large cities Walvis Bay and Swakopmund are supplied with water. Besides, the water supply of the Rossing Mine (one of the largest uranium mines of the world), the associated town of Arandis and other settlements in the region, aresupplied from the Kuiseb area.

Abbildung in dieser Leseprobe nicht enthalten

Fig.5 : Kuiseb river basin with its alluvial aquifers and precipitation isohytes, Benito et al. (2010) .

3. Methods, classification, valuation and management

In the field of ecological economy the dealing with the assessment of ecosystem services, func­tions and goods has gained increasing importance and attention in the last decades (de Groot et al., 2002). Various different schemes to classify ecosystem services were developed. In a period of ten years (1997-2007) Feld et al. (2009) analysed 531 indicators published in 617 peer-re­viewed articles, that should monitor the biodiversity loss and provided ecosystem services. As you can see a “jungle” of different indicator approaches developed in a short period of time re­sulting in classification schemes that are not comparable with each other.That's why I will focus on the most favoured classification worked out by the Millenium Ecosystem Assesment which differs the following four classes: provisioning, regulating, supporting and cultural services (Nai- doo et al., 2011) (Fig. 6). Other concepts like for example the one from De Groot et al. (2002) follow an approach which is based on four main ecosystem functions: regulation, habitat, produc­tion and information. From these functions, ecosystem goods and services are generated that result in three categories of values: ecological, socio-cultural and economic values.

Abbildung in dieser Leseprobe nicht enthalten

Fig. 6: Categories of ecosystem services (Adapted from MA, 2005).

3.1 Payments for ecosystem services (PES)

Considering a sustainable development, “Payments for ecosystem services (PES) programmes are widely recognized as novel and innovative mechanisms that seek to promote the conservation of biodiversity while simultaneously improving human livlihoods” (Naidoo et al., 2011: 445).

Wunder (2005) defines PES by using five criteria to describe its principle:

[...]