1. SEGURA PRB Water Exploitation Index+ (WEI+)
Monthly, three-monthly and seasonal calculations
Adolfo Mérida Abril
Javier Gras Treviño
19-20 December 2011, Prague

2. WEI+ Data 19-20 December 2011, Prague
* Annual WEI+ does not include Storage
19-20 December 2011, Prague

3. WEI+_monthly Calculation:
Data series used to calculate WEI+_monthly goes from jan.1989 to dec
The distribution of the irrigations demands are as follow:
Storage variation data is the difference between the volumes stored in two consecutive months. The released volume is added to monthly contributions resulting in Internal flow:
* If (Vtn-1 – Vtn)> 0; Stn = Vtn- Vtn-1
* If (Vtn-1 – Vtn) <=0; Stn = 0
19-20 December 2011, Prague

4. WEI+_monthly Desalination volume is included as a water resource.
Water requirements are calculated as 10% of the natural average Inflow, plus 2.33 hm3/month, knowing that 28 hm3 is the annual demand for natural ecosystem, according to the current Water Mangement Plan.
Returned volume is calculated as a percentage of urban and irrigation demand. These percentages are specified in the Segura River Basin Water Management Plan (1998):
Returned volume of irrigation : 8.5% of irrigation demand
returned volume of urban demand : 77% of urban supply
Water abstraction data for Urban supply are obtained from real data between 1989 and 2010.
Water abstractions values for irrigation are obtained accordin to real crops and their theoretical demands. Information based on current Water Management Plan from 1998
External demands are also included as a Water abstraction: water transfer for urban supply and irrigation to other basins.
19-20 December 2011, Prague

5. WEI+_monthly: including storage.
(*) The water abstraction (TWA) is represented over the water availability (RWA)
WEI+_monthly average is 163%.
19-20 December 2011, Prague

6. WEI+_three-monthly (WEI+_3)
To calculate WEI+_3 the same set of data used for calculating WEI+_monthly was used.
Monthly series were accumulated to obtain three-monthly accumulated data.
WEI+_3 average is 161%.
Dry periods are also identified by this indicator.
(*) The water abstraction (TWA) is represented over the water availability (RWA)
19-20 December 2011, Prague

7. WEI+_annual accumulated (WEI+_12)
Calculation:
WEI+_12 was calculated accumulating 12 consecutive months.
This WEI+_12 is compared with WEI+_monthly, WEI+_3 and Segura RB Drought Index (Ie).
19-20 December 2011, Prague

8. WEI+ annual (average year with desalinization)
Comparing WEI+ indexes
Results:
Conclusions:
For WEI+_1 y and WEI+_3 average values are almost equal, while average of WEI+_12 is a bit higher.
WEI+_ annual is the lowest one. To calculate this index total desalination volume of 2010 was used, which is the highest volume in the series, while for the other items average were calculated using the whole series. Therefore basin total current resources are higher than the average of the data series.
Both WEI+_monthly and WEI+_3 have a great annual variability but WEI+_3 is smoother and less intense than WEI+_monthly.
These index detects quite well the dry periods that occurred during the period study at any of the three scales used. This dry periods are the same ones detected by Segura RB Drought Index (Ie basin): 1993 to 1995 and 2005 to 2008.
WEI+ 1 average
163 %
WEI+ 3 average
161 %
WEI+ 12 average
174 %
WEI+ annual (average year with desalinization)
139 %
19-20 December 2011, Prague

9. Comparing WEI+ indexes
Conclusions:
Calculating monthly, three-monthly WEI+ and WEI+_12 some scarcity problems can be detected: months with high demands or lower precipitation.
Calculating only annual WEI+ some of this scarcity periods can be masked: annual resources can be enough to meet annual demands even though some months demands can not be met and some months demands are over-covered.
In Segura RB months in which Demands > Resources, these demands are met using storage water.
Monthly WEI+
181%
Monthly WEI+ with storage
163%
19-20 December 2011, Prague

10. Calculation: WEI+_seasonal
This indicator was calculated obtaining the average value of every season of all the calculation items in the period of study.
WEI+_seasonal average is 158%, which is very close to the indicators mentioned above.
This indicator also detects very well the dry periods that occurred during the period study.
19-20 December 2011, Prague

11. WEI+_seasonal Conclusions:
WEI+_winter
126%
WEI+_spring
183%
WEI+_summer
199%
WEI+_autumn
124%
Conclusions:
During autumn and winter there are not scarcity problems except for a few years.
Is during spring and summer where scarcity problems are really important and frequent at Segura RB due to irrigation demands are very high in this basin.
WEI+ is a useful tool to detect not only resource problems but also demand problems that can be controlled through policy tools.
19-20 December 2011, Prague