Evaluation of different downscaling techniques for hydrological climate-change impact studies at the catchment scale

Hydrological modeling for climate-change impact assessment implies using meteorological variables simulated by global climate models (GCMs). Due to mismatching scales, coarse-resolution GCM output cannot be used directly for hydrological impact studies but rather needs to be downscaled. In this study, we investigated the variability of seasonal streamflow and flood-peak projections caused by the use of three statistical approaches to downscale precipitation from two GCMs for a meso-scale catchment in southeastern Sweden: (1) an analog method (AM), (2) a multi-objective fuzzy-rule-based classification (MOFRBC) and (3) the Statistical DownScaling Model (SDSM). The obtained higher-resolution precipitation values were then used to simulate daily streamflow for a control period (1961–1990) and for two future emission scenarios (2071–2100) with the precipitation-streamflow model HBV. The choice of downscaled precipitation time series had a major impact on the streamflow simulations, which was directly related to the ability of the downscaling approaches to reproduce observed precipitation. Although SDSM was considered to be most suitable for downscaling precipitation in the studied river basin, we highlighted the importance of an ensemble approach. The climate and streamflow change signals indicated that the current flow regime with a snowmelt-driven spring flood in April will likely change to a flow regime that is rather dominated by large winter streamflows. Spring flood events are expected to decrease considerably and occur earlier, whereas autumn flood peaks are projected to increase slightly. The simulations demonstrated that projections of future streamflow regimes are highly variable and can even partly point towards different directions.     

Ichthyoplankton spatial distribution and its relation with water column stratification in fjords of southern Chile (46°48′–50°09′S) in austral spring 1996 and 2008

The occidental shore of the southern tip of South America is one of the largest estuarine ecosystems around the world. Although demersal finfish fisheries are currently in full exploitation in the area, the fjords south of 47°S have been poorly investigated. Two bio-oceanographic cruises carried out in austral spring 1996 and 2008 between 47°S and 50°09′S were utilized to investigate the spatial distribution of fish eggs and larvae. Small differences in the environmental conditions were identified in the top 200 m of the water column between years (5.3–10.5 °C and 0.7–33.9 units of salinity in October 1996; 6.3–11.5 °C and 1.2–34.2 units of salinity in November 2008). The low salinity surface layer generated a highly stable water column within the fjords (Brunt–Väisälä frequency, N>0.1 rad/s; wave period <60 s), whereas a well-mixed water column occurred in the gulfs and open channels. For both years, the ichthyoplankton analysis showed that early life stages of lightfish Maurolicus parvipinnis were dominant (>75% total eggs and >70% total larvae) and they were collected throughout the area, irrespective of the water column stratification. However, other components of the ichthyoplankton such as Falkland sprat Sprattus fuegensis, rockfish Sebastes oculatus, and hoki Macruronus magellanicus were more abundant and found in a wider range of larval sizes in less stable waters (N<0.1 rad/s). Oceanic taxa such as myctophids (Lampanyctodes hectoris) and gonostomatids (Cyclothone sp.) were collected exclusively in open waters. The October 1996 observation of Engraulis ringens eggs in plankton samples corresponded to the southernmost record of early stages of this fish in the Pacific Ocean. We found a significant negative relationship between the number of larval species and N, and a significant positive relationship between the number of larval species and wave period. Therefore, only some marine fish species are capable to utilize fjords systems as spawning and nursery grounds in areas having high amounts of freshwater discharges and very high vertical stratification during austral spring season.     

Latitudinal patterns of export production recorded in surface sediments of the Chilean Patagonian fjords (41–55°S) as a response to water column productivity

The Chilean Patagonian fjords region (41–56°S) is characterized by highly complex geomorphology and hydrographic conditions, and strong seasonal and latitudinal patterns in precipitation, freshwater discharge, glacier coverage, and light regime; all of these directly affect biological production in the water column. In this study, we compiled published and new information on water column properties (primary production, nutrients) and surface sediment characteristics (biogenic opal, organic carbon, molar C/N, bulk sedimentary δ¹³C_org) from the Chilean Patagonian fjords between 41°S and 55°S, describing herein the latitudinal pattern of water column productivity and its imprint in the underlying sediments. Based on information collected at 188 water column and 118 sediment sampling sites, we grouped the Chilean fjords into four main zones: Inner Sea of Chiloé (41° to ～44°S), Northern Patagonia (44° to ～47°S), Central Patagonia (48–51°S), and Southern Patagonia (Magellan Strait region between 52° and 55°S). Primary production in the Chilean Patagonian fjords was the highest in spring–summer, reflecting the seasonal pattern of water column productivity. A clear north–south latitudinal pattern in primary production was observed, with the highest average spring and summer estimates in the Inner Sea of Chiloé (2427 and 5860 mg C m^?2 d^?1) and Northern Patagonia (1667 and 2616 mg C m^?2 d^?1). This pattern was closely related to the higher availability of nutrients, greater solar radiation, and extended photoperiod during the productive season in these two zones. The lowest spring value was found in Caleta Tortel, Central Patagonia (91 mg C m^?2 d^?1), a site heavily influenced by glacier meltwater and river discharge loaded with glacial sediments. Biogenic opal, an important constituent of the Chilean fjord surface sediments (Si_OPAL ～1–13%), reproduced the general north–south pattern of primary production and was directly related to water column silicic acid concentrations. Surface sediments were also rich in organic carbon content and the highest values corresponded to locations far away from glacier influence, sites within fjords, and/or semi-enclosed and protected basins, reflecting both autochthonous (water column productivity) and allochthonous sources (contribution of terrestrial organic matter from fluvial input to the fjords). A gradient was observed from the more oceanic sites to the fjord heads (west–east) in terms of bulk sedimentary δ¹³C_org and C/N ratios; the more depleted (δ¹³C_org ?26‰) and higher C/N (23) values corresponded to areas close to rivers and glaciers. A comparison of the Chilean Patagonian fjords with other fjord systems in the world revealed high variability in primary production for all fjord systems as well as similar surface sediment geochemistry due to the mixing of marine and terrestrial organic carbon.     

Spatial and Temporal Variations in <Emphasis Type="Italic">Pyrodinium bahamense</Emphasis> Cyst Concentrations in the Sediments of Bioluminescent Mangrove Lagoon,St. Croix,USVI

Mangrove Lagoon, located on the island of St. Croix, US Virgin Islands (USVI), is one of few actively bioluminescent lagoons in a location experiencing significant anthropogenic impacts. The bioluminescence is due to an abundance of the dinoflagellate Pyrodinium bahamense in the water column. We recovered surface sediments and sediment cores from Mangrove Lagoon to analyze the spatial distribution and temporal variability of P. bahamense cysts in this system. Surface sediment P. bahamense cyst concentrations ranged from 0 to 466 cysts g^?1 dry sediment, with higher abundances associated with elevated surface water nutrient concentrations and a mixed terrestrial–marine organic matter source regime. In combination with available bioassay data, we hypothesize that phytoplankton utilize nutrients rapidly and subsequent decay of organic matter makes nutrients available for dinoflagellates at the sediment–water interface in the eastern and northern quadrants of the lagoon. However, the nutrients are rapidly exhausted during counterclockwise lagoon circulation resulting in the decline of primary productivity and dinoflagellate abundance in the western quadrants. Downcore profiles suggest that P. bahamense blooms have been occurring for decades, declining in recent years. No cysts were present in sediments predating dredging activities of the 1960s that created Mangrove Lagoon. Recent reductions in cyst abundance may be the result of limited primary productivity caused by restricted water exchange with Salt River Bay due to shallowing of a sill at the mouth of the lagoon. This research highlights the need for more comprehensive geochemical and fossil analyses to better understand long-term ecological variability and inform conservation efforts of these unique habitats.     

Great South Bay After Sandy: Changes in Circulation and Flushing due to New Inlet

The coastal ocean model FVCOM is applied to quantify the changes in circulation, flushing, and exposure time in Great South Bay, New York, after Superstorm Sandy breached the barrier island in 2012. Since then, the lagoon system is connected to the Atlantic via five instead of four inlets. The model simulations are run on two high-resolution unstructured grids, one for the pre-breach configuration, one including the new inlet, with tidal-only forcing, and summer and winter forcing conditions. Despite its small cross-sectional size, the breach has a relatively large net inflow that leads to a strengthening of the along-bay through-flow in Great South Bay (GSB); the tidally driven volume transport in central GSB quadrupled. The seasonal forcing scenarios show that the southwesterly sea breeze in summer slows down the tidally driven flow, while the forcing conditions in winter are highly variable, and the circulation is dependent on wind direction and offshore sea level. Changes in flushing and exposure time associated with the modified transport patterns are evaluated using a Eulerian passive tracer technique. Results show that the new inlet produced a significant decrease in flushing time (approximately 35% reduction under summer wind conditions and 20% reduction under winter wind conditions). Maps of exposure time reflect the local changes in circulation and flushing.     

A land-use-based modelling chain to assess the impacts of Natural Water Retention Measures on Europe’s Green Infrastructure

This article details the process of integrating models to answer a specific policy-driven question: ‘What could be the impact of proposed Natural Water Retention Measures (NWRMs) on Europe’s Green Infrastructure (GI)?’ It describes the new Land Use Modelling Platform (LUMP), now enabling a high spatial scale (100-m) and large coverage (pan-European), whereby several sector-specific models contribute to assessing the impact of regional-level policy on a given spatial topic of concern. The configuration (land claims and land allocations modules) and calibration (accessibility and biophysical suitability) of the LUMP are explained. Four NWRM scenarios (riparian areas, afforestation, grassland and baseline scenario) are configured to run the simulations. For the reference: year 2006, the spatial representation of GI is based on land-use features of a refined version of the CORINE Land Cover (CLC), and resumed as connected components made of nodes and links.

Mathematical morphological image processing and network graph theory model, available from the free software package GUIDOS (the Joint Research Center of the European Commission), enabled the measurement of the GI connectivity and identified most critical links. Results show that the competition for land claimed by different economic sectors, combined with policy-driven rule-sets for the implementation of different NWRMs, yields very different results for the 2030 land-use projections, and subsequently for the morphology of GI. Three indicators associated with the morphology of GI are computed in order to assess the model outputs for 2030. The indicators are computed to answer the following questions: (1) How is the quantity of GI affected by each of the NWRM, and what proportion of that GI is most valuable? (2) What is the location of the most critical nodes and connectors of GI, and what land-use conversions occur under these? (3) Are the average components getting larger or smaller?

Whereas the grassland measure results in the largest net increase of GI, the afforestation measure results in the overall largest number of hectares of key nodes and links within the network. Land conversions occur under the critical GI nodes and links, with a large increase in agricultural areas, especially for the riparian measure under critical nodes and the grassland measure under critical links. Also predominant is the swapping of land from pasture to forest under critical links with the afforestation measure. The riparian measure most increases the average size of GI components, and all three measures contribute to bridging two large components which were divided in the 2006 land-use map, thus increasing the size of the largest component by more than 50%.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.