I am helping some students with their environmental projects.
How is the streamflow drought index (SDI) calculated?
I see there are many methods online but which one is the best for the Europe? What are the differences in these methods? Which one is the most precise and which one gives the best approximation?
Are there any good softwares to calculate the SDI?
Streamflow levels are a useful indicator for drought as well as floods, but they must be used with considerable caution. For streams that are regulated, the stream flow may reflect management decisions at upstream reservoirs which will not reflect true drought conditions. Streams that are unregulated are better for drought monitoring. A hydrograph is used to show stream discharge (water level) over time.
The already given answerts are pretty good, nevertheless, if you still have doubts perhaps you should go to following reference in which the use of SPI is clearly explained:
Tallaksen, L. M., & Van Lanen, H. A. (2004). Hydrological drought: processes and estimation methods for streamflow and groundwater (Vol. 48). Elsevier.
Best regards
Published
by Jorge Jódar, Senior Hydrogeologist en Hydromodel Host, S.L.
Streamflow levels are a useful indicator for drought as well as floods, but they must be used with considerable caution. For streams that are regulated, the streamflow may reflect management decisions at upstream reservoirs which will not reflect true drought conditions. Streams that are unregulated are better for drought monitoring. A hydrograph is used to show stream discharge (water level) over time. You can checak these site http://www.ewra.net/ew/pdf/EW_2008_23-24_06.pdf Here SDI calculations are given. Hope this work. Best luck with your work. And National Tech University of Athens has some software dev - http://www.ewra.net/drinc/ must be free to download. (its called DrinC software)
One way we look at the issue of below normal or above normal streamflow is to prepare a cumulative departure hydrograph in the SW USA. First determine the long-term mean. Subtract this from each years flow and then accumulate the difference. The result is a graph the ascends then descends. This will show periods od draught and fluvial periods. It will also indicate what period would be appropriate for determining the mean. This is important since the wrong period will mislead, and this has happened with the Colorado River.
Origins: Developed by Nalbantis and Tsakiris using the methodology and calculations of SPI as the basis for their work.
Characteristics: Uses monthly streamflow values and the methods of normalization associated with SPI for developing a drought index based upon streamflow data. With an output similar to that of SPI, both wet and dry periods can be investigated, as well as the severity of these occurrences.
Input parameters: Monthly streamflow values and a historical time series for the streamflow gauge.
Applications: Used to monitor and identify drought events with reference to a particular gauge, which may or may not represent larger basins.
Strengths: The program is widely available and easy to use. Missing data are allowed, and the longer the streamflow record, the more accurate the results. As with SPI, various timescales can be examined.