National watershed health diagnosis: A pressure-state-response assessment of Iran's 3rd-order watersheds

Watershed health has yet to be considered across scales, particularly at the national level, for effective resource management. However, such an important endeavor is lacking for degrading environments worldwide at high resolution. This study, therefore, addresses the research gap in national-scale watershed health (WH) and ecological security (ES) assessments for 640 3rd-order watersheds (approximately 253,521.4 ± 226,998.4 ha) in Iran. Following the Pressure-State-Response (PSR) framework, 527 nationwide, up-to-date, and accessible variables were initially selected. These were subsequently reduced to 111 non-collinear predictors using the Variance Inflation Factor (VIF) method. The methodology integrated geospatial, climatic, hydrological, and anthropogenic data across Iran's watersheds. The results of compiling different determinants and performing time-consuming, tedious calculations reported means of 0.47 ± 0.02 and 0.25 ± 0.05 for WH and ES across Iran, respectively. Crucially, WH disproportionately depends on institutional responses (64.36 %), overshadowing entrenched pressures (20.32 %) and critically fragile ecological states (15.32 %). The findings indicate that most watersheds in Iran exhibit moderate WH but are trending toward degradation, reflecting increasing environmental pressure and declining ES. The analysis highlights that climatic and anthropogenic factors, particularly rising temperatures, land-use changes, and hydrological disturbances, are the primary drivers of this decline. Widespread degradation underscores the urgent need for integrated watershed management, nature-based measures, climate-adaptive strategies, and transformative governance to mitigate the decline in WH and ES in Iran. • Some 87 % of Iran's watersheds are in moderate condition, with a negative trend. • Response (64.36 %) outweighs pressure (20.32 %) and state (15.32 %) effects. • Thermal extremes and terrain instability drive the watershed pressure index (P). • Atmospheric pollution is the top stressor in the watershed state index (S). • About 87 % of watersheds show low resilience capacity in response index (R).