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- Arid regions 31
- Agriculture 18
- Precipitation (Meteorology) 12
- Groundwater 10
- Irrigation 10
- Technology 8
- Watersheds 8
- Climate 7
- Rain and rainfall 6
- Hydrology 5
- Demography 4
- Aquifers 3
- Brackish waters 3
- Deserts 3
- Droughts 3
- Economics 3
- Livestock 3
- Water quality 3
- Dry farming 2
- Finance 2
