Traditional Biomass involves wood fuels, agricultural by-products and dung which are burned for cooking and heating purposes. This source of energy is therefore easily available and covers a crucial role in accommodating energy demand of over two billion people living in developing countries. (IEA 1998) indicates that the share of biomass in the global energy consumption has remained roughly the same over the last 30 years ranging from 14 to 15% of the global final energy consumption, while accounting for more than 90% of household energy consumption in some developing countries. Only recently this trend has shown a decreasing pattern thanks to the adoption of new environmental policies. According to the (IEA 2006), in 2004, almost 10% of world primary energy demand came from traditional biomass.

As pointed out by (IEA 2006) about 1.3 million people - mostly women and children - have died prematurely due to causes directly linked to the exposure to indoor air pollution from biomass. Therefore forecasting the future pattern of traditional biomass consumption is crucial to the understanding of the consequences linked to the use of traditional biomass.

The inclusion of traditional biomass module in WITCH model is performed by modelling the correlation between economic growth and use of traditional biomass as source of energy and projecting the share of traditional biomass of total energy demand across regions.

In WITCH, the quantity of primary energy supply of traditional biomass at time $$t$$ and for each witch region $$n$$ is defined as follow:

$Q_{trbiomass, t, n} = TPES_{t,n} \cdot \frac{\phi_n \cdot (1- r)}{1+ \phi_n \cdot (1- r)}$

where $$phi$$, the share of traditional biomass on total primary energy supply, is given by:

$\phi_{n} = \left(\frac{Q_{trbiomass_{t_{0}}}}{TPES_{t_{0}}}\right) \cdot \left( \frac{1}{r}\right)$

where $$Q_{trbiomass_{t_{0}}}$$ and $$TPES_{t_{0}}$$ are the supply quantity of traditional biomass and the total primary energy supply at time $$t_0$$, respectively.

What is $$r$$? Scientific literature has dealt with the relationship between economic growth and consumption of biomass energy. (Kammen, Bailis, and Herzog 2001) and (Berndes, Hoogwijk, and Broek 2003) find an inverse relationship between gross domestic product and the use of traditional biomass. Hence, we relationship between economic growth and demand for traditional biomass as follows:

$r = min \left(1, \quad \alpha + \beta \cdot \ln \left( GDP_{PPP} \right) \right)$

### References

IEA. 1998. World Energy Outlook. OECD/IEA.

IEA. 2006. World Energy Outlook. OECD/IEA.

Kammen, Daniel M, Robert Bailis, and Antonia V Herzog. 2001. Clean Energy for Development and Economic Growth: Biomass and Other Renewable Energy Options to Meet Energy and Development Needs in Poor Nations. UNDP New York.

Berndes, Göran, Monique Hoogwijk, and Richard van den Broek. 2003. “The Contribution of Biomass in the Future Global Energy Supply: A Review of 17 Studies.” Biomass and Bioenergy 25 (1). Elsevier: 1–28.