they use this information to estimate the average value of infrastructure stock (calculated at 70% of GDP). This average value is used to extrapolate results for the rest of the countries until 2030. Thirdly, they use the independent estimates of future needs approach that aggregate the estimates from three different sources: (i) Global Water Intelligence for the water sector; IEA (2011) for the power sector and OECD (2012) for the remaining infrastructure sectors. Based on these three approaches, they estimate that global infrastructure investment requirements for 2013-2030 range from US$57 trillion to US$67 trillion, or about US$3.2 trillion to US$3.7 trillion annually on average.

The OECD (2006) report concluded that global infrastructure investment requirements across the transport (road, rail), telecom, electricity and water sectors would amount to around US$53 trillion over 2010-30, or about US$ 2.7 trillion annually average. Annual investment requirements for these sectors amount to some 2.5% of world GDP, which would rise to 3.5% of GDP; if electricity generation and other energy-related infrastructure investments in oil, gas and coal are included. The methodology used built on existing estimates, and extrapolates those to 2030. For the transport sector, they apply the estimated regional level elasticity (the ratio of paved road capital stock in USD billion to GDP) from Fay and Yepes (2003) assuming a fixed convergence rate. Asset replacement is calculated by assuming the economic life provision of 30 years without controlling by the current quality level. For the water sector, they extrapolate the proportion of GDP allocated to water services, varying from 0.3% to 2% based on different levels of income. For telecoms, they identify the underlying trends and drivers, and extrapolate the percentage of GDP invested in telecoms from Fay and Yepes (2003. Lastly, for the energy sector, they adopt estimates from IEA’s World Energy Outlook, which uses a scenario approach to analyze the possible evolution of energy markets to 2030.

There are other estimations in the literature, however, they are based on Fay and Yepes (2003), McKinsey (2013), and OECD (2006). For example, Kennedy and CorfeeMorlot (2013), based on OECD work, are in the high part of the range, with annual investment requirements estimated at US$ 6.6-7.2 trillion when buildings and vehicles included at low carbon (2°C) scenario, and US$ 2.7-3.2 trillion when those are excluded. Using McKinsey’s (2013) estimates of infrastructure investment requirements, KPMG (2014) and Standard & Poor's Ratings Services present the annual investment requirements of $3.2 trillion by 2030. The World Economic Forum’s (2013) estimation of annual infrastructure spending need for 2020 is calculated by taking the Fay et al (2010) estimate of US$ 1.25-1.5 trillion annually in 2013 and assuming a 4% annual growth rate from 2013-20, and an additional US$ 200-300 billion annual requirement to make the infrastructure sustainable (by providing for climate change mitigation and adaptation).

There have been previous efforts to calculate regional estimates, but some of them are outdated and do not account for changes in infrastructure stock or have significant 4