Physical Predictand Drivers and Characteristics of Aridity Across East Africa

ABSTRACT Climate change is increasingly altering global dryland ecosystems, which support nearly 38% of the world's population. East Africa (EA), where approximately 75% of the land is classified as arid or semi‐arid, is particularly vulnerable to these shifts. This study investigates whether aridity in EA is expanding or contracting in response to global warming and identifies the dominant climatic drivers of these trends. Using the De Martonne Aridity Index (), we assess aridity changes over the past 34 years and classify climate types based on aridity duration. Our findings reveal that EA predominantly experiences arid and semi‐arid conditions, with values ranging between 10% and 30%. Wet years (1981, 1982, 1986, 2006 and 2013) exhibit persistent arid conditions ( < 10) in eastern Kenya and central Tanzania, whereas the Lake Victoria Basin and Uganda experience humid conditions (28 ≤ < 35%). Conversely, dry years (1984, 2000, 2005, 2009 and 2014) intensify arid and semi‐arid conditions across Kenya and Tanzania. Empirical Orthogonal Function (EOF) analysis indicates that temperature fluctuations exert a stronger influence on aridity patterns than precipitation, explaining 82.2% of the total variance in the leading mode (EOF1) compared to 40.2% for rainfall. Further analysis establishes a significant correlation between regional aridity and major climate indices, particularly the South Asian Summer Dipole (SASD) showing the strongest positive correlation ( r = 0.44), followed by the IOD ( r = 0.32) and Nino3.4 ( r = 0.16). These findings underscore the growing role of temperature‐driven evaporative demand in shaping EA's aridity patterns, highlighting the urgent need for adaptive strategies to mitigate its impacts on agriculture, water resources, and regional livelihoods.