Assessment of Vapour Pressure Deficit Trends and Their Connections to Climate Variability in the Nile Delta

ABSTRACT Vapour pressure deficit (VPD) is a crucial determinant of land‐atmosphere interactions; however, its long‐term dynamics in intensively irrigated deltaic regions are not well comprehended. This study analyzes three decades (1990–2020) of VPD variability in Egypt's Nile Delta, a transitional area affected by both Mediterranean humidity and Saharan aridity, utilising MERRA‐2, GLDAS and ERA5 reanalysis datasets, which have been validated against data from 16 ground stations ( r > 0.95; Willmott's d > 0.94). Trend analyses utilising the Modified Mann–Kendall test indicate a statistically significant increase in atmospheric aridity (+0.08 to +0.09 kPa decade −1 , p < 0.01), with the most substantial increases observed in summer (+0.114 kPa decade −1 ). Spatial heterogeneity is apparent, with consistently high VPD in the southern and eastern regions of the Delta, whereas coastal areas experience some moderation due to maritime influence. Partial correlation analyses reveal that increasing air temperatures and decreasing relative humidity are the principal factors driving these changes, further exacerbated by soil moisture depletion, which collectively hastens the shift towards enhanced atmospheric aridity. This study highlights the importance of explicitly integrating VPD into climate diagnostics, irrigation management and adaptation planning by characterising the Nile Delta as a representative agroecosystem under deltaic conditions. The changing trajectory of the Delta serves as a regional warning and a globally pertinent case study on how a warming climate intensifies atmospheric water demand and alters agricultural resilience in intensively irrigated deltaic regions.