Relationship between meteorological and hydrological drought

Drought forecasting plays an important role in the planning and managing water resources as well as developing associated mitigation measures. A meteorological drought is defined by low rainfall and is the most commonly studied drought type locally and globally. However, the extent of meteorological drought doesn't necessarily explain the impact of the drought on the hydrology and the water availability. The aim of this study is to explore the relationship between the commonly studied meteorological drought and the hydrological drought in order to use the latter in drought preparedness plans. In this study, the rainfall based Standardized Precipitation Index (SPI) and the streamflow based Standardized Hydrological Drought Index (SHDI) were used to assess the relationships between meteorological and hydrological drought characteristics. SPI and SHDI were applied to 30 catchments in the Murray Darling Basin in Australia. Both indices identified landmark historical drought events over the 1970-2010 period, with significant perturbation in the drought characteristics defining the two drought types. However, SHDI identified fewer drought events compared to SPI, confirming the fact that a low rainfall condition doesn't necessarily lead to a low stream flow condition. The correlations between SPI and SHDI were poor when the entire 30 stations were considered although reasonably good correlations existed for individual catchments. This confirms that there could be homogenous regions or catchment based differences between the two indices. Relationship between two drought types can be explained by catchment and climatic conditions