Case studies from many countries indicate that even when rainfall is high drought can still occur. Droughts have been recorded in Bangladesh, where the rainfall is 2,300mm per year, and in Luang Prabang, Laos, where the annual rainfall is 3,200mm. Similarly, the highest Standardized Precipitation Index (SPI) value of 2.78 indicates a possibility of floods in Cambodia. Identification of a threshold SPI value is necessary to pinpoint impending drought. Since SPI values reflect only the rainfall situation and not the existing water availability in reservoirs and canal systems, such a detailed impact-assessment study should also compare the duration of a negative SPI value with that of reduction in the available water from various sources, including groundwater, reservoirs, and canal irrigation systems. So drought occurs not only because of lack of rainfall but also because of bad practices of water usage and water management.
Shaw, R., Nguyen, H., Habiba, U. and Takeuchi, Y. (2011), "Chapter 9 Proactive Drought Risk Reduction Approaches in the Asian Monsoon Region", Shaw, R. and Nguyen, H. (Ed.) Droughts in Asian Monsoon Region (Community, Environment and Disaster Risk Management, Vol. 8), Emerald Group Publishing Limited, Bingley, pp. 163-186. https://doi.org/10.1108/S2040-7262(2011)0000008015
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