## 3 Results and Discussion
### Evaluation of CHIRPS-Based SPEI  
The correlation coefficients demonstrate a statistically significant relationship between the CHIRPS precipitation estimates and the observed data for calculating the SPEI across various timescales. Most stations show moderate-to-strong correlations, with coefficients ranging from 0.5 to 0.92. Notably, stations like Bouchane (\(r\) = 0.89 for SPEI-12 and \(r\) = 0.87 for SPEI-6) and Dyke of Safi (\(r\) = 0.92 for SPEI-12) have exceptionally high coefficients,  
Figure 3: Scatter plots comparing CHIRPS data with observed rainfall data for multiple stations on monthly scale.  
suggesting excellent agreement between the two datasets (Figure S1 and Table S1). All the stations with \(p\)-values < 0.05 confirm the reliability of these correlations.  
Regarding the BIAS, most stations show values close to zero in the CHIRPS estimates, reflecting good alignment with observed precipitation. However, a few stations, including Benguerir (BIAS = 0.04 for SPEI-3 and SPEI-12, and BIAS = 0.05 for SPEI-6), Bouchane (BIAS = 0.02 for SPEI-1), Chichaoua (BIAS = 0.03 for SPEI-3), and Skhor Rehamna (BIAS = 0.06 for SPEI-12, and BIAS = 0.05 for SPEI-6), show slightly higher BIAS values. Nevertheless, these values remain acceptable, particularly for the extended timescales (Figure S1 and Table S1).  
The RMSE values mostly range from 0.4 to 0.9 across the stations. We observe lower RMSEs (\(\leq\)0.6) in the coastal zone (RMSE = 0.39 mm/month for SPEI-12, RMSE = 0.54 mm/month for SPEI-6), Essaouira-Chichaoua Basin (Adamna: RMSE = 0.57 mm/month for SPEI-12, Talmest: RMSE = 0.51 mm/month for SPEI-12), the Rehamna Plateaus (Skhor Rehamna: RMSE = 0.53 mm/month for SPEI-12, RMSE = 0.58 mm/month for SPEI-6), and Rehamna Plain (Bouchane: RMSE = 0.45 mm/month for SPEI-12, RMSE = 0.5 mm/month for SPEI-6), particularly for the longer timescales. In contrast, higher RMSEs (>0.9) are found at the stations in the High Atlas foothills, such as Iloudjane (RMSE = 0.97 mm/month for SPEI-6) and Sidi Bou-Othman (RMSE = 0.96 mm/month for SPEI-12), likely due to the region's complex topography (Figure S1 and Table S1).  
The comparative analysis of SPEI-12 between the observed station data and the CHIRPS satellite rainfall estimates at four stations (Adamna, El Massira Dam, Iloudjane, and Nkouris) reveals localized differences in assessing drought intensity (Figure 4). While these differences are apparent, the overall statistical metrics, particularly correlation and the BIAS, indicate highly acceptable results (Figure 4). For example, at the Adamna station in Essaouira-Chichaoua Basin, the CHIRPS data consistently underestimates drought intensity during specific periods (1983, 1992, 1995, 1999-2000, 2007-2008, 2012-2013, and 2016-2017) and overestimate it during others (1985, 1990 and 2009-2010) (Figure 4). Similar patterns occur at the El Massira Dam station in the Rehamna Plateaus, Iloudjane station in the High Atlas foothills, and the Nkouris stations in mountainous regions (Figure 4). These discrepancies likely arise from inherent data errors, such as measurement inaccuracies, missing data, and the complexity of regional topographies (67; 68).  
In summary, the CHIRPS-based SPEI is consistent with the observations, making it a reliable tool for drought characterization in Morocco, especially outside mountainous regions. This approach is widely used globally for assessing drought conditions (67; 69; 70).