As I'm writing this delegates from the four competing cities that are vying to host the 2020 World Expo are preparing to pitch to the judges behind closed doors in Paris. The winner will be revealed tonight. What's not clear exactly how sustainable any of the winning bids would be. 

The favourite is Dubai, whose theme is connectivity. If it wins, it will be the first time that a Middle Eastern city has hosted a World Exposition. The other contenders are Yekaterinburg in Russia, whose theme is globalisation, ?zmir in Turkey, whose theme is health, and São Paulo in Brazil, whose themes are diversity and harmony. Each have very strong cases to make.

Dubai

The title for the United Arab Emirates' showcase is "Connecting Minds, Creating the Future". It seeks to use the event to present and explore a renewed vision of progress and development based on shared purpose and commitment. Three subthemes have been identified as key drivers of global development: Sustainability, Mobility and Opportunity.

It expects to spend Dh25 billion on the event and generate 277,000 new job opportunities over the next seven years. Development will occur on a 438-hectare site on the southwestern edge of Dubai next to the new Al Maktoum International Airport, which will be able to carry 160 million passengers a year.

The site itself would be divided in three areas dedicated to each sub theme. These thematic zones would lead up to Al Wasl, the main plaza. Countries would be able to set up their pavilion in the area that corresponds best to their development strategy. UAE claims that sustainability is at the heart of the project, though this is difficult to see at this stage.

The site is based on a modular design: an important part of the Expo will be dismantled and rebuilt to create appropriate infrastructures for the development of the region: the Dubai Trade Center, an Expo museum, a university, apartment buildings etc. Some of these facilities are permanent and will be utilised for other purposes after Expo 2020.

It aims to generate half of the power for the site sustainably.

Ekaterinburg

Home to more than 1.3 million citizens, the city is a centre of education, research, culture and industry where tourist attractions include seven wooden churches built without a single nail. The proposed theme of the city's Expo bid is 'The Global Mind', which is an attempt to explore globalisation, its consequences, threats and challenges.

The prospective site is 500 hectares wide and just 5km from the city center. 180 ha of the site would be dedicated to the Expo and the rest of the area would host permanent accommodation, commercial centers and leisure space along with parks and parking lots. "We want to create a real smart city that everyone can benefit from," said Russia's Deputy-Prime Minister Arkady Dvorkovich.

?zmir

Turkey lost out to Milan for the 2015 Expo, and is offering Izmir instead of Ankara for the 2020 bid, with the theme 'New Routes to a Better World: Health for All'. With a population of about four million, it is by far the oldest city competing, as it has seen the influence of numerous civilisations, from the Hittites to the Romans, Mongolians and the Ottomans. The city says it wants to be the place to solve medical mysteries and dangerous diseases while hosting the world fair.

It is focusing its bid in accordance with the Millenium Development Goals and the UN's post 2015 agenda, conceiving health as a basic human right that has to be promoted through international cooperation and public policies. The bid identifies four challenges that should be tackled during the Expo: Education and Public Health, Innovation, Care and Collaboration and Healthy living.

The Expo would cover about 205 ha and would be located around a natural lagoon bisected by a road. Nature conservation would have to play an important part in the design of the site since many trees surround the natural lagoon and numerous bird species like flamingos live in the area.

The bidders hope that solar and geothermal energy would feed the energy requirements of the site. After the Expo, the site would become a public park, to offer a relaxation space to the health centre.

São Paulo

With over 70 nationalities living together in a city of 11 billion, Sao Paulo's economic and cultural power stems from diversity. The city's bid aims at fostering the notion that diversity is an ally to development.

Diversity of thought, of cultures, of skills enables innovation, creative economy and new possibilities for human progress. However, as diversity can be a source of conflict and discrimination for some, the Expo bid also intends to tackle this issue by analyzing the role of public policies, the notion of prosperity and the importance of cross-cultural dialogue.

The 500 ha site is in the region of Pirituba, in the north-east of the city, an area currently covered by rainforest, lakes and rivers, much of which would be destroyed. "It was important to take into account the geography and the typography of the area, the local culture, the social dimension of the Expo, as well as the objective to welcome 30 million visitors" shared Ralf Amann, architect and Director of GMP Brazil.

The area is badly connected and contains very few job opportunities so there are plans to build a new metro line connecting it to the city center and construct a huge new hub for business, tourism and education with research and learning centers, convention centers and so on.

Possibly by the time you're reading this the winner will be known. You will have to visit www.bie-paris.org to find out, or follow #expo2020 on Twitter. Good luck to everyone!