Sharp Increase in June to August Minimum Temperature in 2013 over Rwanda: Assessment of Possible Potential Causes and Related Changes in Atmospheric Circulation Patterns
Rwanda, a landlocked agricultural country, experienced escalating climate risks since 2013 due to rising June to August (JJA) minimum temperatures (Tmin), harming farming zones, lowering yields, risking health, and threatening economy. This study examined drivers of Rwanda’s 2013 warming anomaly that severely affected eastern/central lowlands, analyzing circulation changes (1983-2021) using multiple datasets including Enhancing National Climate Services for Rwanda (ENACTS-Rwanda), European Centre for Medium-Range Weather Forecasts Reanalysis 5th Generation (ERA5), and National Oceanic and Atmospheric Administration (NOAA) observations. Methodologies included Empirical Orthogonal Function (EOF) decomposition, Mann-Kendall trend tests, Sen’s slope estimator, and composite analysis to quantify trends and atmospheric linkages. Results showed a significant post-2013 Tmin increase (+0.4？C to +2.1？C) exceeding maximum temperature (Tmax) trends. EOF analysis identified a dominant warming mode (72% variance, loadings to +0.872) linked to coupled processes such as increased vertical descending, increased 850-hPa specific humidity, increased low-level cloud cover, but reduced precipitation, which collectively promoted nighttime warming through warm advection. The anomaly was amplified by El Ni？o-Southern Oscillation (ENSO)-induced Pacific warming and enhanced East African moisture transport. These findings demonstrated how local thermodynamic processes interacted with global climate, forcing them to produce extreme Tmin conditions. The results suggested adaptive strategies, including heat-resistant crop cultivation and optimized water management, could mitigate agricultural impacts. Future research should incorporate these mechanisms into regional climate models while quantifying non-meteorological contributions to observed warming trends, providing critical insights for climate resilience planning in Rwanda and similar regions.
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