Influence of climate change on water partitioning in agricultural watersheds: Examples from Sweden

Future climate change is predicted to increase precipitation volume in Sweden, and also to modify precipitation patterns and produce more intense rainfall events. This study examined the impact of such changes in three small Swedish watersheds dominated by agricultural land. The Soil and Water Assessment Tool (SWAT) was used to investigate the relationship between changes in precipitation (monthly and daily) and monthly water partitioning between runoff, soil water content, and evapotranspiration. A climate ensemble produced from Representative Concentration Pathway (RCP) scenarios 4.5 and 8.5 and five different global climate models, regionalized by the Swedish regional climate model RCA4, was used to feed the SWAT model. The results showed similar outcomes for the three sites, with an increase in total monthly precipitation often associated with an increase in high daily rainfall events. Increased intensity of rainfall, particularly events > 15 mm/day, was associated with an increase in runoff, but not in soil water content. In the few cases where monthly precipitation decreased, soil water content also decreased. The main impact on all hydrological components of the system appeared to be more significant during the middle of the cropping season (May?August) than at the beginning (April) or end (September). These conclusions emerge despite the climate model ensemble underestimating the heaviest daily rainfall events. Overall, this study showed that the projected increasing trend in seasonal rainfall in southern Sweden would not result in more soil water being available for crop production.