DPSIR - Impact Indicators

While the scenario setup describes the pressures on the hydrological cycle in the Upper Drâa region for the coming decades, the model results are indicating the concluding state of the system. As foreseen by the DPSIR-framework, the impacts on the natural and socio-economic system should be quantified by using adequate state or impact indicators. Only then responses (according to the socio-economic scenarios) can be anticipated. Within the Upper Drâa Catchment three economically meaningful dimensions of water availability can be identified:

1. in the upstream oases

2. at the reservoir Mansour-Eddahbi 3. on the rangelands

16 Data available from the investors (available at http://www.ouarzazate-lake-city.com/ [last access 09.05.2009]).

Within the following sections appropriate indicators are chosen in order to describe the scenarios impacts on these domains.

5.6.3.1 Irrigation of Upstream Oases

Most oases in the Upper Drâa Valley are dependent on surface water for the irrigation of cropland and orchards. The use of the Standardized Runoff Index (SRI, see section 4.2.3) is discarded, since the procedure defines drought based on a probability distribution, independent from demand and supply. For example the upstream oasis of M’Semrir never experiences water scarcity, whereas the SRI indicates drought as soon as discharge falls below a certain threshold. Therefore an absolute indicator is preferred. The fraction of years in which 70 % of the irrigation demand calculated can be satisfied by surface water seems as an adequate indicator, since the irrigation demand is calculated based on the crop mix in a wet year. As the variability of the climate scenarios equals that of the baseline scenario (see section 5.6.1) no assessment of distribution and length of dry spells can be made.

5.6.3.2 Reservoir Inflow

Water released from the reservoir Mansour-Eddahbi is the main irrigation source for irrigated agriculture in the Middle Drâa Valley. Furthermore the drinking water for the city of Ouarzazate is abstracted from the reservoir. In the Upper Drâa Valley one of the most considered variables is the discharge to the reservoir. Due to the buffering function of the reservoir, the seasonal variation of the inflows does not inhibit the provision of irrigation water to the Middle Drâa catchment when needed; hence the assessment of annual discharge seems adequate.

In order to compare the changes in runoff to changes in water availability in other domains, the use of the annual SRI has been considered. But due to the normalization involved only little deviations were obtained and again the use of absolute metrics is favored.

An annual discharge to the reservoir of 300 Mm³ is required to sustain irrigation in the Middle Drâa valley and drinking water supply, furthermore it compensates for evaporation losses from the reservoir (see section 3.1). Therefore the exceedance probability of an annual discharge of 300 Mm³ is chosen as an essential impact indicator. Furthermore the average annual discharge is considered, as the reservoir can buffer short-term variations of annual discharge. Within the reservoirs water balance module a threshold of reservoir operation ability has been set, by comparing the reservoir storage capacity with the water demand of the Middle Drâa Valley plus the water demand of the city of Ouarzazate. This threshold is arbitrary, but can easily be replaced by more meaningful thresholds, e.g. considering

biological processes in the reservoir, such as eutrophication and algae growth (Douma et al.

2009; Sadani et al. 2004). Furthermore the water release, which includes water release when storage capacity is exceeded, is considered.

5.6.3.3 Rangelands

In the agropastoral system of the Upper Drâa Valley rangelands in different elevation zones sustain livestock throughout the year. On these pastures fodder availability is dependent on seasonal rainfalls. As pointed out in the model validation section (5.5.6), the imperfect modeling of soil water disallows the use of soil water data to assess rangeland condition.

Furthermore biomass development and yield have neither been calibrated nor validated and grazing pressure is not considered in the model. Since plant growth, especially that of brushes and grasses, in the Upper Drâa Catchment is highly dependent on precipitation (Baumann 2009; Roth 2009), the assessment of rangeland conditions in the scenarios is carried out by using the climate data and climate scenario data only. The hydrological model is not used for the assessment. Nevertheless the results are presented as a by-product to cover the whole sphere of agricultural activity in the research area. For a more detailed assessments of rangeland productivity in the Upper Drâa valley under the pressure of global change see Baumann (2009) and Roth (2009) as well as Fritzsche (2011)

Table 5-27: Spatiotemporal extent of rangelands in the Upper Drâa Catchment (see section 3.6)

Season Elevation Zone [masl]

Spatial Extent

[km²] Months

Spring 2000-2500 2496 March-May

Summer >2500 1353 June-August

Fall 2000-2500 2496 September-November

Winter <2000 10978 December-February

Due to the shallow soils in the research area and the exceedance of precipitation by potential evaporation throughout the year, no additional benefit of the PDSI compared to the SPI could be stated, as the soil storage is almost always empty. Therefore the SPI is considered as an appropriate proxy for rangeland condition. Precipitation data is aggregated spatially for the different season’s ranges and temporally for three month averages to reflect the spatiotemporal change in rangeland use (section 3.6 and Table 5-27).