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Topic
- Deserts 44
- Agriculture 21
- Groundwater 14
- Technology 11
- Hydrology 10
- Irrigation 10
- Reclamation of land 9
- Water quality 9
- Watersheds 8
- Aquifers 7
- Building 7
- Climate 6
- Bureaucracy 5
- Economics 5
- Politics and government 5
- Demography 4
- Pipelines 4
- Precipitation (Meteorology) 4
- Water-supply 4
- Arid regions 3
