Model scope and structure

General

The model covers land use, energy and water systems, along water with selected impacts on and from climate change. The past years in the model domain show snapshots of these systems as per available historical data. For future years, investments in infrastructure and intra-annual operation of the supply chains are optimised such as to meet given demand projections at the minimum net present cost and constrained by resource availability. The final demands for which projections are included in the model are:

• Agriculture: demand for food crops and livestock heads;

• Water: demand for water for rural and urban domestic uses, for tourism and for mining;

• Energy: aggregated demand for electricity from all sectors (with load profile), and annual demand for fuels in agriculture, commercial & services, industrial, residential, transportation and other sectors (without profile).

A general representation of the boundaries of the model (i.e. the aspects / supply chains included) is given below. Note that also a number of links between the energy, land use and water systems are included. These links make so that, as the demands listed above are met in one system, additional resources from our systems are required, potentially creating conflicts in the use of resources. Including these links in the model makes it a nexus model, useful for looking at the cross-system impacts of sectoral decisions and reaching policy coherence across sectors.

figure upcoming

Discount rate

The model minimises the Net Present Value of all costs incurred according to the above representation. The costs are discounted using the following discount factor.

Discount factor	Source
4.30%	Technical Working Group

Time horizon

The model is solved for the period 2019-2040 in annual increments. Each year is subdivided into two seasons (from January to April and from May to December) and each of them further into two day parts (07:00-18:00 and 18:00-07.00).

Details of the systems represented

Below we give details of each of the represented systems.

Energy system

The energy system representation includes all the energy uses across Namibia’s economic sectors, divided by fuel and sector, according to UN stats balances. List of the fuels and sectors included is given below.

Fuels - Unit of demand: PJ

Designation of commodities	Description
ELC001	Electricity for transmission network
ELC002	Final electricity
NGS	natural gas
HFO	heavy fuel oil
BIO	Biomass
COA	Coal
HYD	Hydro energy
SOL	Solar energy
WND	Wind energy
DSL	Diesel
KER001	Kerosene
GSL	Gasoline/petrol
KER002	Aviation fuel
LNG	Liquified Natural Gas
LPG	Liquified Petroleum Gas

Sectors - Note: in the model, the designation of the sector always precedes the name of the fuel. Note also that the power sector is represented separately, in detail. It contains a detailed techno-economic representation of all the coversion processes from primary fuels to electricity.

Designation of sectors	Description
AGR	Agriculture
COM	Commercial and services
IND	Industry
OTH	Other
PWR	Power
RES	Residential
TRA	Transportation

Fuels - Unit of demand: PJ

The technologies included in the representation of the energy sector, that is, the processes that supply or convert the fuels listed above, are listed below.

Technologies

Designation of technologies	Description
IMPHFO	Import of heavy fuel oil
IMPCOA	Import of coal (from South Africa)
IMPKER001	Import of kerosene
IMPKER002	Import of aviation fuel
IMPLNG	Import of LNG
IMPLPG	Import of LPG
IMPDSL	Import of diesel
IMPGSL	Import of gasoline/petrol
MINNGS	Mining of natural gas
MINBIO	Production of biomass
MINHYD	Hydro resource
MINSOL	Solar resource
MINWND	Wind resource
PWRBST	Dummy technology generating electricity
PWRBIO001	Biomass power plant
PWRHFO001	Heavy fuel oil power plants
PWRCOA001	van Eck coal power plant
PWRCOA002	new coal power plants
PWRDSL001	Anixas & Paratus plants
PWRNUC001	new nuclear power
PWRSOL001	Grid-connected solar PV
PWRSOL002	Rooftop solar PV
PWRSOL003	Concentrating Solar Power (CSP) 4 hours
PWRSOL004	Concentrating Solar Power (CSP) 8 hours
PWRSOL005	Concentrating Solar Power (CSP) 12 hours
PWRTRN001	Transmission & Distribution network
PWRHYD001	Ruacana hydro power plant
PWRHYD002	Potential Baynes large hydro power plant
PWRWND001	Wind turbines
PWRNGS001	New natural gas combined cycle power plant
PWRNGS002	New LNG combined cycle power plant
PWRNGS003	New LNG gas turbine

The figure below gives a schematic representation of the power sector part of the model, since this is represented in particular detail, and investments therein are optimised.

Land system

The land and water system is represented in an integrated way where each unit of land has a water balance (i.e. precipitation = evapotranspiration + runoff + groundwater recharge). Competition for land in driven by the demands for crops, built up land and other drivers and allocated to different uses by the optimization process. Land use change may then lead to changes in water availability as the relative shares of evapotranspiration, runoff and groundwater recharge will differ for different land uses.

Land covers

The following land covers are included in the model. Agricultural land is not listed, as it is split in several more categories (see ‘Agricultural land representation’ below).

Designation of land use	Description
LNDBAR	Barren land and savanna
LNDBLT	Built-up land
LNDFOR	Forest and woody savanna
LNDGRS	Grassland
LNDOTH	Shrubland
LNDWAT	Water bodies and wtlands

Agricultural land representation

The agricultural land is further divided into uses for crops and uses for livestock. The following crops and livestock categories are included.

Designation of commodity	Description
CRPCAB	Cabbage
CRPDAT	Dates
CRPGRP	Grapes
CRPMAI	Maize
CRPMTP	Pearl millet
CRPONI	Onion
CRPPTW	White potato
CRPSOR	Sorghum
CRPWHE	Wheat
LVSCTL	Cattle
LVSGOT	Goats
LVSPIG	Pigs
LVSSHP	Sheep

The land use representation is based on the GAEZ methodology developed by the International Institute for Applied Systems Analysis (IIASA) and the Food and Agriculture Organization (FAO). The GAEZ database provide geospatial estimates of climate variables and land suitability for crop cultivation. Crop production can be either irrigated or rainfed and fall under one of 3 managements systems as depicted in the figure below. Allocation will be based on the relative cost-effectiveness of each production regime subject to constraints on investments and constraints on resources (e.g. water and land area).

Low level inputs Under a low level of inputs (traditional management assumption), the farming system is largely subsistence based. Production is based on the use of traditional cultivars (if improved cultivars are used, they are treated in the same way as local cultivars), labour intensive techniques, and no application of nutrients, no use of chemicals for pest and disease control and minimum conservation measures.

Intermediate level inputs Under an intermediate level of input (improved management assumption), the farming system is partly market oriented. Production for subsistence plus commercial sale is a management objective. Production is based on improved varieties, on manual labour with hand tools and/or animal traction and some mechanization, is medium labour intensive, uses some fertilizer application and chemical pest disease and weed control, adequate fallows and some conservation measures.

High level inputs Under a high level of input (advanced management assumption), the farming system is mainly market oriented. Commercial production is a management objective. Production is based on improved or high yielding varieties, is fully mechanized with low labour intensity and uses optimum applications of nutrients and chemical pest, disease and weed control.