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

Effect of Diet, Anthropogenic Activity, and Climate on δ\u3csup\u3e15\u3c/sup\u3eN Values of Cave Bat Guano

Few studies have attributed δ15N values of guano to a factor other than diet. A δ15N record obtained from a 1.5-m core of bat guano deposit from Zidită Cave (western Romania) provides a record of anthropogenic and climatic influence on the regional nitrogen pool. Nitrogen content is nearly constant (%N \u3e 9) for over 1 m of the core, indicating limited diagenesis. The δ15N and δ13C time series are compared and the δ15N is also interpreted in light of previously published pollen assemblage from the same core. Using these comparisons the influence of anthropogenic activity and water availability is interpreted. Although some δ15N variation can be attributed to major changes in anthropogenic activities, additional variation implies an alternative control. The correlation between δ15N and δ13C values is significant (p \u3c 0.01), but not strong, suggesting that both variables are influenced by water availability, known to be a primary control of δ13C values within C3 ecosystems. Drier periods indicated by higher δ13C values correspond with lower δ15N values and vice-versa for wetter conditions. The instrumental climate record (precipitation amount) for the past 50 years nearby the cave supports this relationship. From 1000 to 1800 CE, the δ15N values fluctuated between 11.5 and 14‰, then decreased in two abrupt steps, at 1800 and 1947 CE. The most significant decrease occurred after 1947 CE when values fell from 12.5 to below 7‰, suggesting the N-cycle transitioned towards a more conservative state. The correlations between δ15N and δ13C, and the instrumental precipitation record, along with the apparent negligible effect of diet on long term δ15N variation indicate that the δ15N values of guano can be used as an integrator of the local N-cycle