Variability and Change in Water Cycle at the Catchment Level

This study proposes a simple methodology for assessing future-projected evolution of water cycle components (precipitation, potential evapotranspiration, and potential runoff) based on the two-level Palmer model of the soil and their impact on drought conditions at basin level. The Palmer Drought Severity Index (PDSI) is used as drought metric. The catchments of rivers Arges, Mures, Prut, Siret and Somes (mid- and lower Danube basin) have been chosen as case studies. The present climate data consist of Romanian gridded dataset, monthly precipitation and values of streamflow from Romania and Republic of Moldova and potential evapotranspiration-related data from the Climate Research Unit (University of East Anglia). We used as future projections five numerical experiments with regional models obtained through the EURO-CORDEX initiative, under two Representative Concentration Pathway scenarios. The correlations between observed streamflow at the river basin outlets and PDSI-related components of the water cycle show that PDSI represents reasonably well processes taking place in the selected catchments. Depending on the specific scenario and catchment, droughts that in the Palmer classification were deemed as incipient, mild or severe under present climate will become a normal summer feature toward the end of this century, especially over catchments situated in the lower Danube basin