The study documents a decades-long decline in the seasonal open-water area in Klamath Marsh using the Landsat imagery archive and a wetland classification algorithm. Between 2003 and 2021, the maximum annual open-water area of the marsh declined by about 50 percent. 

The decline in open-water area of the Klamath Marsh was determined to be due to declining streamflow into the marsh and declining groundwater level beneath and surrounding the marsh. The changes in streamflow and groundwater level could not be attributed to human water use and management, nor to changes in precipitation. Declines in the marsh open-water area, groundwater level, and streamflow were concurrent with an increase in the annual mean air temperature across the region and indicate that climate-related changes in evapotranspiration processes may be responsible.  

The study highlights the need to factor the impact of rising temperatures into decision making processes involving water management and forecasting in the Klamath Basin.