1. PROPOSAL AND RECOMMENDATIONS FROM
THE TWG TO THE WS&D EG
ON THE WEI+ INDICATOR

2. Context
As states the Mandate “The aim of the Expert Group is to provide pragmatic and simple indicators for both water scarcity and drought in order to provide a clear picture throughout the EU”.
Aim of the TWG
The Technical Working Group (TWG) was established in order to solve the identified open issues in relation to the Water Scarcity Indicator WEI+.
The goal of the TWG was to assist to the WS&D EG with WEI+ pending issues, propose and test relevant solutions and come up with concrete suggestions for the whole EG to be discussed and adopted.

3. THE BIG CHALLENGE From the WEI…..
The original water exploitation index (WEI), was defined as the mean annual total abstraction of fresh water divided by the long-term average freshwater resources.
Traditionally has been applied at country scale and long term average
…to the WEI+
Improve spatial scale (River Basin District, river basin or sub-basin)
Improve time scale (Annual-Monthly scale)
New variables to better reflect water scarcity situations (returns, eflows, …)

4. MODUS OPERANDI OF THE TWG
What we have done…..
- Three technical meetings (Prague, Brussels (I), Brussels (II)
- Two testing exercises
- A lot of discussions via , phone calls, etcetera.
We have been reviewing three different aspects of the WEI+
- Conceptual aspects
- Potential variables to be included in the WEI+
Formulation
Thresholds

5. POTENTIAL PARAMETERS TO BE INCLUDED
“AVAILABILITY”related parameters
“DEMAND”related parameters
Precipitation (P)
Water Abstraction (ABS)
Actual Evapotranspiration (Eta)
Water Demand (DEM)
Internal Flow (D = P-Eta)
Water Use (USE)
External Inflow (ExIn)
Outflow (Out)
Water Requirements (WR)*
of which: Environmental Flows (EF)
Returned Water (R)**
Storage (S) – Change in Storage (ΔS)
Natural Runoff (Qnat)

6. WATER ABSTRACTION / WATER DEMAND / WATER USE
RECOMMENDATIONS:
The TWG recommends using preferably the water abstraction parameter since this parameter directly measures how much pressure we are putting into the natural system.
In cases where water demand is significantly higher than water abstractions, the TWG recommends the use of a parallel index that shows the relationships between them. The supplementary indicator would depict the imbalance in the cases where this is a fact.

7. WATER RETURN RECOMMENDATIONS:
The TWG believes that water return is a relevant parameter to characterize actual pressures on natural systems. In this regard recommends this factor be included in the formula to better represent the real problems of water scarcity in the basins.
Given the observed effects on the indicator values​​, the TWG recommends considering the returns in the nominator, as a decrease of the water abstraction, and not in the denominator.

8. ENVIRONEMTAL FLOWS RECOMMENDATIONS:
Environmental Flows should be conceptually considered in the WEI+. At the moment, due to the absence of a harmonized and comparable method of calculation, Eflows should be left out of the WEI+ formula itself at the moment, and be considered instead in the definition of the relevant thresholds.
In order to better reflect hydrological pressures on the natural systems, the TWG recommends to use in parallel a complementary sub-indicator as a relation of observed streamflow with respect to the natural streamflows.

9. RENEWABLE WATER RESOURCES (I)
ESTIMATING RWR
Traditionally Water Resources were estimated as:
Water Availability = P – Eta + ExtIn
However, when trying to apply the WEI+ at monthly scale was observed that many months produced negative results.
Actually, these results showed an over-simplification in the hydrologic balance equation.

10. RENEWABLE WATER RESOURCES (II)
TWO OPTIONS FOR ESTIMATING NWR
Starting from the hydrologic balance equation:
P- Eta + ExIn - Abstractions + Returns - Outflow = ΔSnat + ΔSart
Renewable water resources can be obtained from two different ways:
Option 1. RWR = P- ETa + ExIn - ΔSnat
Option 2. RWR = Outflow + Abstractions – Returns + ΔSart

11. RENEWABLE WATER RESOURCES (III)
RECOMMENDATIONS
Water Resources can be calculated using 2 different options, depending on data availability and the specific conditions in each case.
When estimating natural water resources the TWG recommends using the best option based on available information and certainty

12. WATER RESOURCES FROM ARTIFICIAL RESERVOIRS
RECOMMENDATIONS
Artificial reservoirs provide water resources used specifically to minimize water scarcity situations. If the goal of the WEI+ is to reflect real situations of water scarcity then water resources of artificial reservoirs should be included in the formula.

13. TIME SCALE THRESHOLDS RECOMMENDATIONS
The TWG recognizes that monthly WEI+ best represents water scarcity situations. If acquisition data is not a concern, the TWG recommends applying the WEI+ at monthly scale.
THRESHOLDS
RECOMMENDATIONS
The TWG considers defining thresholds for the WEI+ is challenging and requires further in-depth investigation. Preliminary thresholds could be use considering the environmental and socio-economical relevance of them.

14. SUMMARY
Based on the recommendations adopted by the TWG and results obtained after testing relevant options, the proposed formula of the WEI+ would be:
       
                                                 
In order to better reflect real situations of water scarcity in the basins this formula would be apply preferably at monthly scale, including water resources provided by artificial reservoirs.

15. Regarding how to estimate natural water resources, two different options can be considered in the TWG
Option 1. NWR = P- ETa + ExIn - ΔSnat
Option 2. NWR = Outflow + Abstractions – Returns + ΔSart
However, when estimating natural water resources the TWG recommends using the best option based on available information and certainty”.
To better reflect water scarcity situations, the TWG recommends the use two parallel indexes
Water Demand Index WDI = water demand / water abstraction
RoONS = observed streamflows / natural streamflows