Examining environmental stress changes in response to climate change and land use dynamics in the Colorado River Basin over the past two decades

• Forest degradation affected 5,340 km², highest in Arizona and New Mexico. • 28.9 % of the CRB showed a significant temperature upward trend, averaging 3.98° °C. • Areas with vegetation health and tree cover decline faster than improving regions. • Colorado state experienced the highest environmental stress across the CRB. • Unchanged forests highlight the need to preserve forest cover for sustainability. Climate-induced environmental stress and land use changes pose a growing threat to ecosystem stability, particularly in regions vital to human and ecological well-being. The Colorado River Basin (CRB) stands as a crucial resource for the Southwestern US, supplying water to 40 million people. As the region faces intensifying climate pressures and prolonged drought conditions, understanding these impacts is essential for environmental sustainability. However, comprehensive studies linking environmental stressors to climate change and land use dynamics remain scarce. This study investigated spatiotemporal changes in forest and percent tree cover (PTC) and generated 30 m resolution datasets for actual evapotranspiration (ETa), enhanced vegetation index (EVI), and land surface temperature (LST) using all available Landsat images from 2001 to 2021. The Mann-Kendall test was employed to identify the environmental changes over two decades. Results showed 5,340 km² (3.82 %) of forest degradation, while only 739 km² (0.56 %) reforested. The CRB experienced an average temperature increase of 2.04 °C over two decades, with 28.9 % of the area exhibiting a significant warming trend, on average 3.98 °C, indicating an intensification of heat stress. Furthermore, regions with declining vegetation health and tree cover are deteriorating at a faster rate than areas of improvement, with Colorado state experiencing the highest environmental deterioration. Unchanged forest serves as a baseline with minimal changes, highlighting the importance of preserving forest cover for stable environmental conditions. These findings put into perspective an urgent need for policymakers, planners, and managers to protect forests and rehabilitate degraded lands to sustain ecosystems and adapt to environmental changes.