What is the difference between RDI (Reclamation Drought Index) and RDI (Reconnaissance Drought Index) in calculating drought

The RDI (Reclamation Drought Index) and developed by Weghorst (1996) and it is a hydrological index, but the RDI (Reconnaissance Drought Index) developed by Tsakiris and Vangelis (2005) as a meteorological drought index.

The Reconnaissance Drought Index (RDI) can be characterized as a general meteorological index for drought assessment.The RDI can be considered to provide a more realistic representation of the drought conditions as it incorporates the potential evapotranspiration along with the precipitation and can be effectively used to compare the drought conditions between areas with different climatic characteristics. This is the distinct advantage of RDI as it enables its universal applicability in contrast to other indices.

As an alternative meteorological drought index, the reconnaissance drought index (RDI) was proposed by Tsakiris and Vangelis (2005), utilizing the ratios of precipitation over reference crop evapotranspiration (ET0) for different time scales, to be representative of the region of interest. The reconnaissance drought index (RDI) is based on the precipitation to potential evapotranspiration ratio (P/PET).The RDI was further investigated by Tsakiris et al. (2007). One of the advantages of the RDI index is its sensitivity to drought events.

The SPI has been the popular drought index over the years, since it is based on only precipitation as the primary factor which controls drought conditions. The differences between SPI and RDI may be clearly illustrated when drought severity maps are produced. RDImay also be considered as amore suitable index than SPI for studying drought severity under climate change, since it incorporates both precipitation and potential evapotranspiration, which are directly affected by climate change. Also a strong advantage of RDI is that it offers a rational comparison of drought conditions between areas with different climatic characteristics.

However, possible role of ET0 in the detection of drought events has been instrumental in the development of a new reconnaissance drought identification and assessment index (Tsakiris 2004). Consequently, the reconnaissance drought index (RDI) was proposed by Tsakiris and Vangelis (2005), utilizing the ratios of precipitation over Reference Crop Evapotranspiration (ET0) for different time scales, to be representative of the region of interest. While different time scales can be used, the yearly expression is presented for illustrative purposes.

The Reclamation Drought Index (RDI) was recently developed as a tool for defining drought severity and duration, and for predicting the onset and end of periods of drought. The impetus to devise the RDI came from the Reclamation States Drought Assistance Act of 1988, which allows states to seek assistance from the Bureau of Reclamation to mitigate the effects of drought. The RDI is calculated at a river basin level, and it incorporates the supply components of precipitation, snowpack, streamflow, and reservoir levels. The RDI is adaptable to each particular region and its main strength is its ability to account for both climate and water supply factors.