Hydroclimatic Variability and Its Implications for Drought and Runoff in the Kävlingeån Basin, Southern Sweden (1970–2020)

Understanding the drivers of hydrological change is essential for sustainable water governance. This study examines long-term hydroclimatic variability and drought evolution in the Kävlingeån Basin, southern Sweden, over the period 1970–2020. Trend analyses of precipitation, runoff, and potential evapotranspiration indicate increasing atmospheric water demand accompanied by declining runoff, suggesting an overall tendency toward drier conditions. Drought indices (SPEI-03 and SPEI-12) further reveal increasing drought persistence and pronounced seasonal asymmetry. Monthly trend analysis of SPEI-03 shows significant drying in March and April, coinciding with the onset of the agricultural growing season, which may pose challenges for crop production and irrigation management in this predominantly agricultural basin. Decadal variability analysis towards wet and dry events indicates that SPEI-12 has shifted toward drier conditions since the 1970s, characterized by a reduction in annual mean wet events and an increased frequency of dry events. In contrast, SPEI-03 exhibits no clear long-term trend, suggesting that short-term water balance variability has remained relatively stable.

Furthermore, attribution analysis of multi-year runoff variations suggests that non-climatic factors potentially contribute more to the observed changes than climatic drivers, including precipitation and potential evapotranspiration, indicated by a set of Budyko framework based analysis at yearly and monthly time scale. This finding indicates that human activities have likely played a substantial role in reshaping the hydrological balance of the basin.