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- Agriculture 25
- Irrigation 22
- Groundwater 14
- Watersheds 12
- Politics and government 10
- Climate 8
- Precipitation (Meteorology) 8
- Bureaucracy 7
- Demography 7
- Economic development 7
- Economics 7
- Dams 6
- Water-supply 6
- Industries 5
- Hydrology 4
- Reclamation of land 4
- Soils 4
- Soviet Union 4
- Water quality 4
- Finance 3