Projection analysis of future drought characteristics in Upper Draa Catchment (Southern Morocco)

. The consequences of global warming will aggravate the impacts of droughts. Future drought patterns are important for planning and policy formulation to mitigate the adverse effect of climate change. Consequently, this study aims at examining the projected the drought characteristics in seven meteorological stations in the Upper Draa Catchment (UDC) during the period from 1980 to 2016 using standardized precipitation index. The future climate scenarios were predicted by the model CNRM-ALADIN63 for three periods (2025–2049, 2050–2074, and 2075–2099). The changes were examined based on two Representative Concentration Pathways scenarios, namely: RCP4.5and RCP8.5. The findings indicated that increasingly extreme droughts are anticipated to occur during (2050-2074) followed by (2025-2049) than (2075-2099) under both scenarios. The results reveal a contrast in drought event frequency between historical data and projections with a noticeable variation of patterns of droughts characteristics across stations and time periods. This accentuates how urgent it is for the Upper Draa Catchment to implement proactive water resource management and adaptive strategies.


Introduction
Climate change has led to changes in the intensity and frequency of drought putting pressures on water resources in many countries [1].This risk is poised to amplify due to the shift towards increasingly warmer and drier conditions.Conversely, there is an expected rise in demand for water, driven by the expanding needs of the growing population, industrial, agricultural and energy sectors [2,3].The rise in both drought intensities and frequencies has been observed, particularly in South Europe and in the Mediterranean region [4,5].Considering the diverse trends in precipitation, particularly in Morocco [6], drought characterization and monitoring are essential in arid and semi-arid regions in the climate change context [5,7].To accurately quantify and monitor droughts, several indices have been developed.A commonly adopted drought indicator is the Standardized Precipitation Index (SPI) [8], as advised by the World Meteorological Organization (WMO) [1,9].This index gauges the intensity and duration of droughts, besides providing insight into their severity.This research's goal is to evaluate future temporal fluctuations in drought occurrences in Upper Draa Catchment, using SPI-3 and SPI-12.To achieve this, we apply the CNRM-ALADIN63 model for three periods (2025-2049, 2050-2074, and 2075-2099), based on two distinct representative concentration pathways: RCP 4.5 and RCP 8.5.Through this comprehensive analysis, we aim to provide insights to support environmental sustainability management.
Fig. 1.Geographical location, river system, and elevation of the Upper Draa Catchment.

Data
Observed monthly rainfall data over the period 1980-2016, were collected from the Water Basin Agency of Ouarzazate and the Regional Office for Agricultural Development of Ouarzazate.Twelve meteorological stations (Fig. 1) served to calculate Standardized Precipitation Index (SPI-3 and SPI-12).The CNRM-ALADIN63 regional climate model, obtained from the CMIP6 project [14,15], was chosen to predict future precipitation data for the Upper Draa catchment area.This model has been selected for its reliability and prior application in evaluating climate change in Morocco [8,14].The data is derived from the EUR-11i simulations of the EURO-CORDEX domain at a spatial resolution of about 12.5 km × 12.5 km [13].We considered projection from two concentration pathways (RCP) scenarios namely RCP 4.5 and RCP 8.5, for the period 2025 to 2099.The data were further bias corrected has undergone bias correction [15].

Drought analysis using the SPI index
In the context of the research area, drought analysis was performed by applying the short term (SPI-3) and long term (SPI-12) projected meteorological droughts, considering RCP 4.5 and RCP 8.5 scenarios.Additionally, assessment of drought severity, drought intensity, and drought duration were calculated for the meaningful evaluation of drought conditions in the research area.

Results and discussions 3.1 Extreme Drought Events
To analyse the droughts characteristics, we computed occurrences defined by an SPI lower than − 2 in the historical and future projections under both RCP 4.5 and RCP 8.For 2025-2049 and 2075-2099 periods, findings revealed a higher number of anticipated drought events under RCP4.5 in comparison to RCP 8.5, both for SPI -3 and SPI-12.
Nevertheless, for 2050-2075 drought events are more detected for RCP 8.5 in SPI-3 than in RCP 4.5, while fewer were found for RCP 8.5 in SPI-12 than in RCP4.5.
The analysis reveals that the frequency of drought events in historical data is higher than the projected data.The differences can be attributed to natural climatic variability or other influential factors, such as the cyclic patterns of El Niño and La Niña, which could have contributed to the increased severity of drought events in the past, when compared to the CNRM-ALADIN63 model's projections for the future.
3.2 Future SPI projections (2025-2099) Finally, 5 moderates to extreme droughts with an extreme drought (-3.45) detected from February to July 2093.These predictions highlight the vulnerability of the area to recurrent and intense droughts across different time periods.The presence of extreme droughts among each time period of 21 st century underlines the importance of durable water resource management, adaptive strategies, and the integration of climate resilience measures to mitigate the potential impacts on agriculture, water supply, ecosystems, and overall societal well-being.Additionally, long-term planning and policy formulation should consider the likelihood of such drought events and their potential cascading effects on various sectors.

Conclusion
Anticipating future drought patterns is vital for efficient water resource management, especially in semi-arid and arid regions.This research examined historical data (1980-2016) and projected future drought scenarios using SPI-3 and SPI-12 indices, estimated via the CNRM-ALADIN63 model in the Upper Draa Catchment.The future analysis covers three periods (2025-2049, 2050-2074, and 2075-2099) under RCP 4.5, and RCP 8.5 scenarios.The findings reveal a notable difference in the frequency of drought events between historical records and projected data.In addition, the study displays varying fluctuations in drought duration, intensity, and severity levels across the seven observed stations and different periods.This highlights the importance of proactive water resource management and adaptive strategies in the Upper Draa Catchment.
5 scenarios.As indicated in Fig 2 the average count of SPI values below -2, indicating extreme drought events, exhibits a noticeable pattern.Notably, this pattern reveals that as the time scale expands to an annual assessment (SPI-12), the frequency of SPI values falling below -2 increases significantly.

Fig. 2 .
Fig. 2. Average number of extreme droughts for the historical and the future under RCP4.5 and RCP 8.5 scenarios.

Table 1
illustrates the drought characteristics under RCP 4.5 and RCP 8.5 scenarios

table 1 ,
Agouilal's predictions highlighted 12, 10 and 6 moderate to severe drought events with varying drought severity levels, respectively for the three periods.These events were observed during September to November 2025, September to December 2068, and Projections of SPI-3 under RCP 4.5 for the three periods highlight how both Agouilal and El Mansour Eddahbi Dam are projected to experience mild and severe droughts, especially during the designated months.Severity and duration of droughts are detected for same periods but more intense compared to Mansour Eddahbi Dam.3.2.2 SPI-3 Under RCP 8.5 for the three periodsResult shows that Agouilal is projected to experience 7 moderates to severe droughts with a severe drought (-2.04) occuring from October to December 2048.Additionally, 12 moderates to severe drought with a severe drought (-2.04) detected from October to December 2054 and finally, 6 moderates to extreme droughts with an extreme drought (-2.99) detected from August to November 2092.Mansour Eddahbi Dam, is projected to experience 6 moderates to severe droughts with a severe drought ( -0.64) moderate to severe drought from September to November 2036.Furthermore, 9 moderates to severe droughts with a severe drought (-0.64) detected from September to November 2070 and finally, 4 moderates to severe drought (-0.64) from September to November 2092.
Additionally, 10 moderates to extreme drought with an extreme drought (-11.43)detected from December 2060 to August 2061.