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WSI - Water Scarcity Index

The WSI was developed by ARPA Veneto for the Piave River basin (North-Eastern Italy) using a methodology based on the analysis of the main hydro-meteorological parameters measured within 9 sub-catchments: discharge, rainfall, snow water equivalent and temperature. This early warning system is a multi-criteria method based on a statistical analysis starting from the hydrological year 1990-1991 (starting date 1 October 1990); the index can be calculated every day during the year by comparing the current situation with past statistics (e.g., quantiles). The WSI was further developed and improved in the Brenta river basin (Trentino Alto-Adige and Veneto Regions, Italy) within the Alpine Space Project C3-Alps, by Veneto Region, University of Padua (Department Tesaf) and ARPA Veneto.


  • Discharge: the minimum mean discharge (sliding window of 10 days) since the hydrological year beginning (1 October), minimum discharges (10 days)) from the 1st of October and the cumulative outflow volumes since the 1st of January
  • Precipitation: cumulative rainfall from the 1st of October and the 1st of December
  • Temperature: the quantiles of air temperature are calculated considering both the mean temperature since the 1st of October and the 1st of March
  • Snow cover height: mean snow cover height (10 days) from the 1st of October and cumulative of fresh snow from the 1st of October
  • Total radiation: further parameter that can be included in the calculation process (discretionary)
Finally the WSI is calculated as the weighted mean of the 9 quantiles above mentioned; the weight is established by experts of hydrology and climatology in order to get more relevance to some parameters depending on weather trend and previous hydrological years.


The WSI is a number ranging from 0 to 1
The WSI standard threshold is acutally fixed at 0,5 (empirically): if the WSI is under this value a potential drought period is coming. WSI that are above the standard threshold but at the same time below the mean historical values deserve particular attention because they may be a sign of forthcoming water scarcity.

WSI is automatically calculated every 15 day during the hydrological year in order to alert the Veneto Region about potential incoming drought periods (WSI under a fixed threshold value).


WSI is a calculation performed using several spreadsheets

Hardware: no special requirements
Software: EXCEL


WSI is a methodology and actually there is not a tool that automatically calculate the index.

Successful experiences in the ASP

Pilot case study at the Brenta river.
» Application and validation of Water Scarcity Index to the Brenta River Basin.pdf

For further information about WSI:

Regional Agency for Environmental Prevention and Protection of Veneto
Regional Department for Land Safety
Hydrological Service
via Tomea, 5 - 32100 Belluno (Italy)
tel. +39 0437 935 600
fax +39 0437 935 601
e-mail: dst@arpa.veneto.it

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