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Topic
- Deserts 21
- Agriculture 11
- Irrigation 6
- Reclamation of land 6
- Bureaucracy 5
- Technology 5
- Watersheds 4
- Building 3
- Climate 3
- Groundwater 3
- Arid regions 2
- Canals 2
- Dams 2
- Demography 2
- Food 2
- Hydrology 2
- Imports 2
- International regimes 2
- Livestock 2
- Politics and government 2
