Distinguishing the Effects of Climate Change and Acid Rain Recovery on Water Chemistry Trends: A Challenging Task?

This study examines whether trends in climate variables—precipitation, runoff, temperature, and actual evapotranspiration (AET)—can help explain changes in water chemistry in 78 Norwegian lakes from 1990 to 2020. AET has increased significantly in nearly all catchments, though substantial discrepancies exist between modeled and calculated values. Temperature has risen at 79% of monitoring stations, whereas precipitation and runoff exhibit significant trends in only 15% and 19% of lakes, respectively. These patterns are reflected in the limited explanatory power of climate variables for water chemistry changes. Spatial and temporal correlations between climate trends and acid rain recovery further complicate distinguishing their individual effects in simple correlation analyses. Overall, climate variables show weak explanatory power for water chemistry trends. However, multivariate redundancy analysis (RDA) provides a non-significant indication that increases in precipitation and runoff may counteract the effects of rising temperatures on water chemistry.