1. Agnew (2000) Using the SPI to identify drought. Drought Network news, Vol. 12, No1, Winter 1999-Spring 2000
2. Allen R, Pereira LS, Raes D, Smith M (1998) Crop evapotranspiration: guidelines for computing crop water requirements. FAO Irrigation and Drainage, Paper No. 56, Rome, Italy, 300pp
3. Alley W (1984) The palmer drought severity index: limitations and assumptions. U.S. Geological Survey, Reston
4. Alston M, Kent J (2004) Social impacts of drought. A report to NSW Agriculture, Centre for Rural Social Research, Charles Stuart University, ISBN 1 86467 149 1
5. ARH-Alentejo (2012) Plano de Gestão de região hidrográfica do Guadiana (Water Resources Management Plan for the Portuguese area of Guadiana’s river basin). ARH Alentejo, MAMAOT, 2012