Standardized Precipitation Index (SPI) Jürgen Vogt Land Management and Natural Hazards Unit Institute for Environment and Sustainability http://desert.jrc.ec.europa.eu/ http://edo.jrc.ec.europa.eu/

Major Comments Add a clear definition Added to Section 1 (Key Message) It is a very good indicator. However one standard deviation represents different drought conditions based on the inherent variability of the climate of each place. SPI is standardized to zero mean and a variance of one. Therefore comparable across different climate conditions. More clearly explained in Sections 1 and 2 (Key Message and Relevance) It would be very interesting to complement SPI categories (defined by standard deviations) with aspects of their ecological-hydrological significance, or in terms of water management. Difficult to add a general statement as impacts will depend on both the natural and socio-economic environment. Add reference to methods for fitting Gamma Distribution Reference to Website of Colorado State University offers first entry point. Pointe dfurther to references at the end of the Fact Sheet. Section 4 (Methodology)

Major Comments How to handle gaps in the time series? WMO: in 30 years maximum 5 years missing and maximum 3 years in a row. Added to Section 5 (Data Source and Frequency of Data Collection) Minimum time period is 1 month Explicitly said in Section 3 (Temporal Scale) It is important to highlight the statement (Section 6b): Care needs to be taken in arid areas with generally low precipitation, where the distribution of rainfall data is significantly deviating from a normal distribution. Reinforced the statement in Section 6b A range of temporal scales need to be available to allow droughts to be characterised for different river basins (shorter periods may be more critical in impermeable upland catchments than permeable lowland catchments (Comment on example shown under Specific Assessment) Tried to make this more explicit in the section.

3-month SPI for 10-12/2008 aggregated to regional level EDO Map Server Products: Precipitation Indicators Modelled Soil Moisture Remote Sensing Indicators SPI: Standardized Precipitation Index 3-month SPI for 10-12/2008 aggregated to regional level http://edo.jrc.ec.europa.eu/

EDO: SPI Regional Time Series Drought events Wet period Como, IT