Abstract
Drought is one of the major challenges affecting water resources, agriculture, and ecosystem resilience in the sub-Saharan region. This study analyzed the spatial and temporal variation of surface water and drought conditions in the Kagera sub-basin using remote sensing indices: the Normalized Difference Water Index (NDWI), Normalized Difference Vegetation Index (NDVI), Soil Adjusted Vegetation Index (SAVI), and Normalized Difference Moisture Index (NDMI). The analysis covered the period from 1985 to 2020 at 5-year intervals. The Standardized Precipitation Index (SPI) was utilized to assess rainfall anomalies, which were then compared with surface water variability and drought intensity indicated by remote-sensing indices. The SPI revealed multiple instances of extreme and severe drought, with higher frequencies observed in the 3-month and 6-month SPI compared to the 12-month SPI. The NDWI revealed significant spatial and temporal variations in surface water area in the Kagera sub-basin. In general, surface water area showed a mixed trend, decreasing from 660 km2 in 1985 to 632 km2 in 2000, and then gradually increasing to 698 km2 in 2020. Additionally, the NDWI exhibited a strong correlation with 3-month and 6-month SPI but a weaker correlation with 12-month SPI. On the other hand, the NDVI indicated significant variations in drought conditions, with areas experiencing severe drought ranging between 446 km2 and 1892 km2. These severe drought events were prevalent from 1990 to 2000. The results also indicated a strong correlation between drought extent and intensity extracted from NDVI and rainfall anomalies, with SPI-3 and SPI-6 showing stronger correlations compared to SPI-12. Moreover, the SAVI results were consistent with those of NDVI, suggesting that the soil brightness effect on the NDVI is not significant in the sub-basin. In contrast, NDMI indicated that severe drought areas generally increased over the analyzed years and exhibited a weak correlation with SPI for all time scales. These findings contribute valuable insights that are important for decision-makers in managing surface water resources and implementing proactive and targeted environmental conservation measures to enhance ecosystem resilience in the Kagera sub-basin.
Published Version
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