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Urban growth alters environmental conditions with major consequences for climate regulation and the exposure of population to heat. Nature-based solutions may be used to alleviate the increasing urban climate pressures, but the climate regulation services that these solutions can supply for and across different urban conditions remains understudied. We comparatively investigate the urban ecosystem service realization (considering the ecosystem service supply and demand spatial interactions) of local climate regulation by vegetated (green) and water-covered (blue) areas across 660 European cities. Results show relatively robust power-law relationships with city population density (average R2 of 0.34) of main indicators of ecosystem service realization. Country-wise fitting for city-average indicators strengthens these relationships, in particular for western European cities (average R2 of 0.66). Cross-city results also show strong power-law relationship of effectiveness in ecosystem service realization with socio-economic measures like Human Development Index and GPD per capita, in particular for the area fraction of city parts with high ecosystem service realization (R2 of 0.77). The quantified relationships are useful for comparative understanding of differences in ecosystem services realization between cities and city parts, and quantitative projection of possible change trends under different types of city growth so that relevant measures can be taken to counteract undesirable trends. [ABSTRACT FROM AUTHOR]

A data-driven screening methodology is developed for estimating nutrient input and retention-delivery in catchments with measured water discharges and nutrient concentrations along the river network. The methodology is applied to the Sava River Catchment (SRC), a major transboundary catchment in southeast Europe, with seven monitoring stations along the main river, defining seven nested catchments and seven incremental subcatchments that are analysed and compared in this study. For the relatively large nested catchments (> 40,000 km 2 ), characteristic regional values emerge for nutrient input per unit area of around 30 T/yr/km 2 for dissolved inorganic nitrogen (DIN) and 2 T/yr/km 2 for total phosphorus (TP). For the smaller nested catchments and incremental subcatchments, corresponding values fluctuate and indicate hotspot areas with total nutrient inputs of 158 T/yr/km 2 for DIN and 13 T/yr/km 2 for TP. The delivered fraction of total nutrient input mass (termed delivery factor) and associated nutrient loads per area are scale-dependent, exhibiting power-law decay with increasing catchment area, with exponents of around 0.2–0.3 for DIN and 0.3–0.5 for TP. For the largest of the nested catchments in the SRC, the delivery factor is around 0.08 for DIN and 0.03 for TP. Overall, the nutrient data for nested catchments within the SRC show consistency with previously reported data for multiple nested catchments within the Baltic Sea Drainage Basin, identifying close nutrient relationships to driving hydro-climatic conditions (runoff for nutrient loads) and socio-economic conditions (population density and farmland share for nutrient concentrations). [ABSTRACT FROM AUTHOR]

Understanding the partitioning of precipitation water among different water fluxes and storage changes in the landscape, and the co-variations of these variables under various hydroclimatic conditions is essential for quantification and management of water resources and climate feedbacks. This study analyses the co-variation of temperature, precipitation, evapotranspiration, runoff and soil moisture anomalies based on data from two alternative sets of global observational and re-analysis products for 1378 catchments across three separate climate regions of Europe over the period 1980-2010. Co-variation details depend on both climatic zone and which of the alternative datasets is used for the analysis. However, consistently across all climate regions and both alternative datasets, the results show stronger correlation of soil moisture and runoff anomalies, than of the former and any of the other studied hydroclimatic variable anomalies. The latter findings of weak correlations include those of soil moisture with precipitation and evapotranspiration anomalies, even though the latter two hydroclimatic variables are commonly considered as most closely linked with soil moisture. The strong correlation between soil moisture and runoff also applies under extreme event occurrences for both wet and dry conditions, with the co-occurrences of extreme soil moisture and precipitation or evapotranspiration events being considerably less well linked. These results indicate soil moisture variations and associated closely linked groundwater table variations as key regulators of runoff variations, through changes in subsurface hydraulic gradients and associated groundwater flows into streams. In contrast, soil moisture and groundwater level variations do not co-vary as much and/or as quickly with precipitation and evapotranspiration anomalies because precipitation may primarily regulate evapotranspiration and, even under no precipitation conditions, there often still remains enough soil water available for the vegetation to keep transpiring and thus maintaining a relatively high evapotranspiration level. Overall, the results of this study emphasize the complex water flux and storage change connections by transport of both water-mass/volume and water-pressure though whole-catchment pathways, including their subsurface water parts, of various lengths. While the transport of water-mass/volume is slow and may take long time over long pathway distances, such as from many parts of the land surface (where precipitation and evapotranspiration act) to nearest stream (where runoff is observed), the groundwater table (i.e., groundwater pressure) and linked soil moisture (and soil water pressure) variations are faster and lead to quick and strong hydraulic gradient and associated runoff change responses along the entire stretches of short and long water pathways. These fast pressure response connections explain the strong correlations found consistently between soil moisture and runoff anomalies in this comprehensive multi-catchment and multi-climate study. [ABSTRACT FROM AUTHOR]

Successful implementation of an international nutrient abatement agreement, such as the Baltic Sea Action Plan (BSAP), requires consistent understanding of the baseline nutrient loads, and a perception of acceptable costs and fairness in targeted reductions of these base line loads. This article presents a general framework for identifying the implications of divergence between different nutrient load quantification approaches, with regard to both cost and fairness criteria outcomes, for the international agreement to decrease nutrient loads into the Baltic Sea as presented in the BSAP. The results indicate that even relatively small divergence in the nutrient load quantification translates into relatively large differences in abatement cost for different Baltic Sea countries. A robust result, irrespective of differences in nutrient load assessments, is a conflict between abatement cost effectiveness and fairness, with relatively poor countries facing heavy abatement cost burdens for cost-effective international load abatement.