Spatial Distribution of Meteorological Droughts in the Maduru Oya Basin in the Dry Zone of Sri Lanka: Implications of Climate Change

Assessing meteorological drought occurrences is crucial due to their potential to lead to hydrological droughts and serve as early indicators for preparing against future hydrological drought events. On the other hand, climate change escalates the risk of droughts in the future. Therefore, this study focuses on the spatial distribution of meteorological droughts in the Maduru Oya basin of Sri Lanka, considering potential climate change impacts. The CNRM-CM6-1-HR climate model was selected from the six chosen Coupled Model Inter-comparison Project (CMIP) Global Climate Models (GCMs) based on comparative plots and objective function values obtained during bias correction. GCMs were bias-corrected using the mean-based method and the variance-based method, with the mean-based method being chosen based on the objective function values. To generate maps illustrating the future drought status of the basin, gridded rainfall datasets were developed using CHIRP satellite data for future scenarios, SSP1-2.6 and SSP5-8.5, with bias correction through non-linear power transformation. Drought conditions were assessed using the Standardized Precipitation Index over a three-month time scale to monitor the occurrence of meteorological droughts. Results indicate increased vulnerability to moderate droughts under the SSP1-2.6 scenario during 2015-2100, particularly in the upstream Maduru Oya basin, with moderate drought occurrences ranging from 8 to 10%. In the context of the SSP1-2.6 scenario, extreme, severe, and moderate droughts demonstrate percentage increments of 18, 16, and −6%, respectively, compared to the historical period. Notably, there is a substantial rise in moderate droughts in the downstream. Conversely, under the SSP5-8.5 scenario, extreme droughts increase by 31%, severe droughts by 2%, and moderate droughts decrease by 4%. These findings highlight the basin's heightened vulnerability to future droughts, emphasizing the necessity for proactive water resource management.