Local Hydrology Research Articles

Changes to the Water Balance Over a Century of Urban Development in Two Neighborhoods: Vancouver, Canada

AbstractHydrological cycles of two suburban neighborhoods in Vancouver, BC, during initial urban development and subsequent urban densification (1920–2010) are examined using the Surface Urban Energy and Water Balance Scheme. The two neighborhoods have different surface characteristics (as determined from aerial photographs) which impact the hydrological processes. Unlike previous studies of the effect of urbanization on the local hydrology, densification of already built lots is explored with a focus on the neighborhood scale. Human behavioral changes to irrigation are accounted for in the simulations. Irrigation is the dominant factor, accounting for up to 56% of the water input on an annual basis in the study areas. This may surpass garden needs and go to runoff. Irrigating once a week would provide sufficient water for the garden. Without irrigation, evaporation would have decreased over the 91 years at a rate of up to 1.4 mm/year and runoff increased at 4.0 mm/year with the increase in impervious cover. Similarly without irrigation, the ratio of sensible heat flux to the available energy would have increased over the 91 years at a rate of up to 0.003 per year. Urbanization and densification cause an increase in runoff and increase risk of surface flooding. Small daily runoff events with short return periods have increased over the century, whereas the occurrence of heavy daily runoff events (return period > 52 days) are not affected. The results can help us to understand the dominant factors in the suburban hydrological cycle and can inform urban planning.

Variation in Stable Hydrogen Isotope Values in a Wetland-Associated Songbird

Stable isotope analysis is often used to identify the geographic origins of migratory bird populations. While this method can accurately predict the provenance of migratory species, stable hydrogen isotope values measured in feathers (δ2Hf) can be variable within a site and may be influenced by differences among age class (second year vs. after second year), type of feather (primary vs. rectrix), year of sampling, species, and local hydrology. In this study, sources of variation in δ2Hf values were assessed in a wetland-associated Neotropical migratory bird, the Prothonotary Warbler (Protonotaria citrea), by comparing δ2Hf values among age classes, sexes, years and feather types in individuals breeding in eastern Virginia, USA. Age and year were found to influence δ2Hf values, with individuals in their second year having more depleted δ2Hf values (-62.43 ± 9.56‰) than individuals older than 2 years (-53.73 ± 9.04‰). Differences between primaries and rectrices were within the range of sampling error (-2.98‰), and there was no effect of sex. For wetland-associated songbirds, age-related differences in the dietary proportion of aquatic vs. terrestrial prey may provide an additional mechanism for differences observed in δ2Hf values between age classes. In studies that use stable isotopes to assign geographic feather origin, researchers should attempt to account for and propagate known variation in δ2Hf values in assignment models whenever possible.

Microclimatic buffering in forests of the future: the role of local water balance

Forest canopies buffer climate extremes and promote microclimates that may function as refugia for understory species under changing climate. However, the biophysical conditions that promote and maintain microclimatic buffering and its stability through time are largely unresolved. We posited that forest microclimatic buffering is sensitive to local water balance and canopy cover, and we measured this effect during the growing season across a climate gradient in forests of the northwestern United States (US). We found that forest canopies buffer extremes of maximum temperature and vapor pressure deficit (VPD), with biologically meaningful effect sizes. For example, during the growing season, maximum temperature and VPD under at least 50% forest canopy were 5.3°C and 1.1 kPa lower on average, respectively, compared to areas without canopy cover. Canopy buffering of temperature and vapor pressure deficit was greater at higher levels of canopy cover, and varied with water balance, implying that buffering effects are subject to changes in local hydrology. We project changes in the water balance for the mid‐21st century and predict how such changes may impact the ability of western US forests to buffer climate extremes. Our results suggest that some forests will lose their capacity to buffer climate extremes as sites become increasingly water limited. Changes in water balance combined with accelerating canopy losses due to increases in the frequency and severity of disturbance will create potentially non‐linear changes in the microclimate conditions of western US forests.

Hydrological responses to land degradation in the Northwest Benin Owena River Basin, Nigeria

Adequate insights into how land degradation alters the hydrology of river basins will help forecast the hydrological impacts of land cover change dynamics, thereby providing unique information required for sustainable river basin management. This study attempts to utilize a multi-dimensional methodology involving the application of the physically based Soil and Water Assessment Tool (SWAT) hydrological model and Partial Least Square regression (PLSR) statistical model to evaluate the response of the hydrological components within the Northwest Benin Owena River Basin (NWBORB) in Nigeria to land degradation. Using the historic land cover maps of 1986, 2002, and 2015, covering the basin, the SWAT model was employed to simulate the hydrological components for each historic year. The PLSR model was utilized to establish a response relationship between land cover changes and hydrological component modification within the basin. Results showed that between 1986 and 2015, 18.56% of the forest was lost, with a major portion (16.19%) gained by plantation. Consequently, annual water yield and surface runoff increased by 18.28% and 17.26% respectively, while annual base flow and actual evapotranspiration decreased by 22.58% and 21.72% respectively. The reduction in forest is strongly correlated with an increase in plantation (−0.833), surface runoff component (−0.723) and water yield (−0.532). Also, expansion of plantation land is strongly correlated with surface runoff components (0.877) and negatively correlated with base flow component (−0.573). Variable Importance of the Projections (VIP) from the PLSR model showed forest (VIP = 1.23), Plantation land (VIP = 1.02) as the most important land cover variables altering the basins' local hydrology. The study clearly shows that forest preservation plays an important role in the regulation of water resources within a river basin. This methodology can be replicated for poorly gauged river basins provided the land cover maps and stream discharge data are available.

Differential Impacts of Land Use and Precipitation on “Ecosystem Water Yield”

AbstractEcosystem evapotranspiration (ET) can approach annual precipitation (P) often leaving a residual [P‐ET], referred to as an ecosystem water yield (WYe). Using a mobile lab, we estimate ET and WYe, in paired forest and nonforest (shrub or grassland) sites along the precipitation gradient (285–755 mm a−1) in Israel. WYe was 69 mm in the dry sites and was further reduced by ∼51 mm by forestation. Both WYe and the impact of forestation increased in the wetter sites, with forestation reducing WYe by >200 mm, equivalent to ∼30% of the local P. This was associated with increase in ET by a factor of 2.2 and 1.8 in the forest and nonforest sites, respectively, along the rainfall gradient. Losses in WYe due to forestation approached a maximum of ∼200 mm above P ∼ 500 mm, but the forest WYe could vary between ∼300 mm at P = 900 mm and ∼100 mm at P = 500 mm (with equivalent change in WYe between 500 and 300 mm in the nonforest sites), reflecting the increasing “hydrological cost” associated with vegetation ET and the expected climate change in these regions. The results quantify the interactions of land use and climate on ecosystem ET, indicating that in dry climates, afforestation impact on WYe varies significantly across small spatial scales and can reduce WYe with significant impacts on local hydrology. Such impact may be diminished by management (e.g., plant species, thinning, and grazing) but should also consider the trade‐offs with other ecosystem services (e.g., carbon sequestration, soil protection, and surface cooling).

Early warning system using tilt sensors in Chibo, Kalimpong, Darjeeling Himalayas, India

The Indian Himalayan regions have been significantly affected by the increase in the frequency of landslide occurrence. Thirty percentage of the worldwide landslide incidents occur in the Himalayan region with 42% of India’s landslide region belonging to Darjeeling–Sikkim Himalayas (NDMA Report, 2011). Several studies have been carried out worldwide on early warning systems considering rainfall history. Although rainfall is one of the criteria which can successfully predict the probability of landslides on a regional scale, it is indeed difficult to understand the risk associated with slope failure. The reason is the spatial variation of rainfall intensity, local soil conditions, geology, hydrology and topography. An early warning and monitoring system is one of the most effective techniques to minimise the disasters influenced by slope instability as it is less expensive and easier than slope reinforcement. A reliable and robust system fitted with microelectromechanical systems tilt sensor and volumetric water content sensors were installed. The sensor monitors the tilting angle of the instrument which was installed at shallow depths, and the variation of tilting angle corresponds to lateral displacement at slope surface. The primary objective was to monitor the tilting angles at various slope sites and to formulate a dependable warning system with a low probability of false alarms in Chibo Pashyor region in the Indian state of West Bengal. Such system would assist in the installation of several low-cost sensors over an active slope as it was difficult to determine the particular section of slope which could fail in the next heavy rainfall. The change in tilting rate would help in establishing thresholds determined empirically. Such system would help in developing an early warning system and also help in calibrating thresholds calculated using empirical techniques.

Hydroclimatic influences and physiographic controls on phosphorus dynamics in prairie pothole wetlands

While wetlands are known as long-term storages or sinks for contaminants, not all are equally effective at trapping phosphorus (P). The prevalence of P-sink behavior in prairie pothole wetlands remains unclear, especially across gradients of human disturbance. The objectives of the current study were three-fold: (1) characterize the spatiotemporal variability of wetland hydrology and wetland water P concentration across a range of prairie potholes; (2) establish the propensity of different pothole wetlands to act as sources or sinks of P; and (3) assess the potential controls of climatic conditions, landscape characteristics, wetland soil physiochemical properties and local hydrology on source versus sink dynamics. Ten intact and three consolidated (i.e., drained) wetlands located in southwestern Manitoba, Canada, were monitored for water level fluctuations and water soluble reactive P (SRP) concentration over two years with contrasting antecedent wetness conditions. Soil cores were also collected to measure soil physiochemical properties such as the equilibrium phosphorus concentration (EPC). Water column SRP concentrations were compared to EPC values to infer the time-variable source versus sink behavior of each of wetland. Statistical analyses were then performed to assess whether the source versus sink behavior of individual wetlands could be linked to their physiographic or hydrologic characteristics. Results show that some wetlands persistently acted as P sinks while others switched between source and sink behavior. Persistent P-sink behavior was more common with intact wetlands, as opposed to consolidated wetlands. Wetland soil texture, storage volume and short-term water level fluctuations appeared to control the source versus sink behavior of individual wetlands. The dominant controls on P-sink behavior identified under dry conditions were, however, different from those identified under wetter conditions. This study therefore highlights the importance of considering the non-stationary nature of P-sorption dynamics and their controls, even at sub-annual timescales, in the prairie pothole region.

The effects of different land use and hydrological types on water chemistry of young glacial ponds

The study aims to examine the effect of ponds on changes in water quality in a young glacial river catchment. The goal was to identify situations where a periodic hydrographic network is formed in outflow-free areas, which is connected with a higher order receiving area, as well as to study the circulation of matter in this type of system. This study answers the following key question: Do ponds affected by areal pollution substantially affect water quality in streams in periods where they become joined with the hydrographic network? The purpose of the research was to identify patterns associated with the functioning of ponds in young glacial areas in northern Poland on the example of the Borucinka catchment. Ponds were selected in order to generate a study sample characterized by different types of land use, local hydrology, and pond surface area. The study focused on the effects of catchment land use on pond water quality and the effects of periodic changes in local hydrology (linkage of surface flows with bodies of water) on pond water quality. Research has shown that land use in a pond catchment yields a substantial effect on pond water quality. The basic reason for the higher concentration of selected ions is close proximity to farms that generate wastewater, which reaches bodies of water in the study area. Seasonal changes in the concentration of biogenic substances were not observed in ponds. Only notable changes in the concentration of total nitrogen were observed due the episodic formation of a hydrographic network consisting of a collection of linked depressions. One of the more surprising findings was that permanently isolated ponds, which theoretically collect catchment pollutants all the time, are characterized by good hydrochemical conditions.

Prediction of land use changes based on Land Change Modeler and attribution of changes in the water balance of Ganga basin to land use change using the SWAT model

Conflicts between increasing irrigated agricultural area, commercial crops, shifting cultivation and ever increasing domestic and industrial demand has already been a cause of tension in the society over water in the Ganga River Basin, India. For the development of sustainable water resource strategies, it is essential to establish interaction between landuse changes and local hydrology through proper assessment. Precisely, seeing how change in each LULC affects hydrologic regimes, or conversely evaluating which LULC shall be appropriate for the local hydrological regime can help decision makers to incorporate in the policy instruments. In this study, hydrologic regimes of the Ganga River basin have been assessed with landuse change. Catchment hydrologic responses were simulated using Soil and Water Assessment Tool (SWAT). Meteorological data from IMD of 0.25° × 0.25° spatial resolution were taken as the climate inputs. Simulated stream flow was compared at different gauge stations distributed across the Gang River and its tributaries. Urbanization has been the topmost contributor to the increase in surface runoff and water yield. While increased irrigation demands were the dominant contributor to the water consumption and also added to the increased evapotranspiration. This study can be important tool in quantifying the changes in hydrological components in response to changes made in landuse in especially basins undergoing rapid commercialization. This shall provide substantive information to the decision makers required to develop ameliorative strategies.

Remote sensing of ecosystem trajectories as a proxy indicator for watershed water balance

AbstractEcosystem trajectories are inextricably linked to hydrology; however, water availability is not easily observed within the landscape. The response of vegetation to soil water availability may provide an indicator of local hydrology and the resilience or sensitivity of ecosystems to long‐term changes in water balance. In this study, vegetation trajectories derived from Landsat Modified Soil Adjusted Vegetation Index over a 22‐year period are used as an indicator of spatio‐temporal changes of watershed water balance and surface water storage within 6 proximal watersheds of the Boreal Plains ecozone of Alberta, Canada. The interactions between hydrology, topography, geology, and land cover type are examined as they relate to vegetation change.In this study, we find that run‐off ratio (run‐off/precipitation) is greater within watersheds with greater variability of relief, compared within subhumid, wetland‐dominated watersheds (average = 0.35, 0.20, respectively), which experience lagged run‐off response. A 2‐year drought had a greater impact on vegetation trajectories within variable relief watersheds containing a high proportion of coarse‐grain surficial geology, compared with peatland‐dominated watersheds. The drought extended for an additional 1 to 2 years within 3 subhumid watersheds, reducing watershed run‐off to less than 50 mm per water year (November to October) in 2 watersheds. However, proportional area of decline of Modified Soil Adjusted Vegetation Index was significantly less within these watersheds. The results of this study indicate that wetlands play an important role for local water balance and ecosystem maintenance during periods of water stress and should be considered within land use planning and reclamation strategies of the Boreal Plains.

Meteoric water lines in arid Central Asia using event-based and monthly data

The local meteoric water line (LMWL) reflects the relationship between stable oxygen and hydrogen isotopes in precipitation, and is usually calculated using an ordinary least squares regression (OLSR). When event-based data are used to calculate a LMWL, the differences in precipitation amount of samples are not considered using OLSR, which in turn may influence the representativeness of the LMWL for local hydrology. Small rain events occur widely in arid Central Asia (annual mean precipitation <150 mm), and where smaller precipitation has lower deuterium excess, this results in LMWLs with slopes and intercepts lower than the global average. Based on an observation network of isotopes in precipitation across the Tianshan Mountains in arid Central Asia, LMWLs for 23 stations are calculated from event-based data from 2012 to 2013 (n = 978), using ordinary least squares, reduced major axis and major axis regressions and their precipitation-weighted counterparts. For the northern slope and mountainous areas, the LMWL slope and intercept are close to the Global Meteoric Water Line (GMWL), but the slope and intercept are lower for the southern slope indicating the greater dominance of sub-cloud evaporation. The effect of moisture recycling in the irrigated areas on the northern slope also can be seen where the LMWL slopes are >8. Using a precipitation weighted regression method with event-based data (especially precipitation-weighted reduced major axis regression, PWRMA) is generally consistent with the OLSR regression using monthly data. However, event-based datasets provide a wider range of values to better constrain the regression than can be achieved using monthly data over a short period, providing a sounder basis for determining LMWLs for relatively short-term sampling campaigns in an arid setting. The use of the PWRMA regression is preferred for determining the LMWL for the Tianshan Mountains, and results in a regional meteoric water line of δD = 7.9δ18O + 10.16.

Assessing artificial oxygenation in a riverine salt-wedge estuary with a three-dimensional finite-volume model

The presence of anoxia and hypoxia is increasingly observed in the bottom waters of many estuaries and coastal embayments, and remains a management challenge due to detrimental effects on estuarine biodiversity and overall amenity. As part of a multi-pronged strategy to tackle the problem of eutrophication in the Swan-Canning estuary, oxygenation plants have been installed in the upper reaches of the estuary to counteract the high oxygen demand and prevent hypoxia. In this study, we developed a three-dimensional hydrodynamic-biogeochemical model to simulate oxygen dynamics and assess the cost-benefit of different oxygenation operation regimes (e.g., night operation, all day operation or tidally-optimised operation). The model accurately captured the salt-wedge dynamics and the extent and severity of hypoxia under low and high flow conditions. The artificial oxygenation is shown to significantly improve oxygen conditions in the targeted zone under low flow conditions. The scenario assessment revealed a two-term power relationship between total oxygen supply and areal benefit, with scenarios highlighting that adding more oxygen would improve the oxygen conditions to a greater extent up to a limit (i.e., the law of diminishing returns). The total areal benefit achieved was found to be dependent on the total oxygen load rather than the timing of the oxygen input regime. The results also suggest that when designing an artificial oxygenation plant for an estuarine environment, the locations of oxygen addition should be carefully selected within the context of the local hydrology to achieve optimum results in target areas.

Palynological and Geochemical Records of Environmental Changes in a Taxodium Swamp near Lake Pontchartrain in Southern Louisiana (USA) during the Last 150 Years

Ryu, J.; Bianchette, T.A.; Liu, K.-B.; Yao, Q., and Maiti, K.D., 2018. Palynological and Geochemical Records of Environmental Changes in a Taxodium Swamp near Lake Pontchartrain in Southern Louisiana (USA) during the Last 150 Years. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 381–385. Coconut Creek (Florida), ISSN 0749-0208.The hydrological and environmental histories of estuarine wetlands in southern Louisiana are not well-documented. To better understand their local developmental processes, a 59 cm sediment core (WMA-1) was extracted from a bald cypress (Taxodium distichum) swamp located approximately 800 m west of Lake Pontchartrain. This area has been heavily influenced by human activities, and is susceptible to inundation from storm surges from Lake Pontchartrain as well as fluvial and lacustrine processes. 210Pb analysis indicates that WMA-1 has a sedimentation rate of 0.39 cm/year, consistent with the detection of a 137Cs peak at 18 cm depth. Sedimentological and geochemical analyses reveal two distinct sedimentological facies: an organic-rich dark brown peat unit from 0 to 29 cm containing low concentrations of terrestrial elements (e.g., Ti, and Fe), and a clay unit from 29 to 59 cm with elevated concentrations of most elements (e.g., Sr, Cl, Ti, Mn, and Fe). The pollen assemblage in the clay section is dominated by TCT (mainly Taxodium), but it is replaced by Salix and wetland herbaceous taxa in the overlying peat. The Taxodium swamp was present at the site at least 150 years ago, and was replaced by Salix and other bottomland hardwood trees and wetland herbs due to a decrease in water level around AD 1940. While climate may have played a role, this hydrological change was most likely caused by the significant regional human activities during the last 100 years. Two thin clay layers (at 3–5 cm, 14–19 cm) embedded in the upper peat section were likely deposited from hurricanes Isaac (2012) and Betsy (1969): two events responsible for heavy rain and significant storm-surge flooding. Our findings suggest that human activities are capable of altering local wetland hydrology and ecology, while the clay layers represent hurricane-induced floods at the site during the past century.

Identifying Feasible Locations for Wetland Creation or Restoration in Catchments by Suitability Modelling Using Light Detection and Ranging (LiDAR) Digital Elevation Model (DEM)

Wetlands play a key role in controlling flooding and non-point-source (diffuse) pollution. They are therefore an important tool for mitigating diffuse water pollution from farms. However, to use this tool, it is necessary to obtain detailed assessments and identification of potential wetland restoration or creation sites. This is complicated by the diversity of landscapes, environmental conditions, and land ownership. Site suitability for wetland restoration or creation depends on many factors: the underlying geology, soils, topography, hydrology, drainage, and land ownership. Local hydrology and soils are among the most important factors. However, the inventory and characterization of a site’s soils and hydrology often requires extensive, expensive, and time-consuming ground surveys, and it is therefore limited to small areas. Another possibility would be to consider topography, which strongly determines water movement patterns. Light detection and ranging (LiDAR) data provides detailed topographic information and can be acquired by remote sensing. Our study showed that terrain analysis using high-resolution topographical data can produce suitability maps for wetlands that can be easily used by decision makers and planners in watershed management. The rapid methodology reveals potential wetland creation or restoration sites at a reasonable cost; with the resulting spatially explicit suitability map, managers can plan for wetland creation or restoration without having to wait for field-data collection.

Using nested discretization for a detailed yet computationally efficient simulation of local hydrology in a distributed hydrologic model

Fully distributed hydrologic models are often used to simulate hydrologic states at fine spatio-temporal resolutions. However, simulations based on these models may become computationally expensive, constraining their applications to smaller domains. This study demonstrates that a nested-discretization based modeling strategy can be used to improve the efficiency of distributed hydrologic simulations, especially for applications where fine resolution estimates of hydrologic states are of the focus only within a part of a watershed. To this end, we consider two applications where the goal is to capture the groundwater dynamics within a defined target area. Our results show that at the target locations, a nested simulation is able to competently replicate the estimates of groundwater table as obtained from the fine simulation, while yielding significant computational savings. The results highlight the potential of using nested discretization for a detailed yet computationally efficient estimation of hydrologic states in part of the model domain.

Hydrologic Response to Land Use Change in a Large Basin in Eastern Amazon

Accelerated land use changes in the Brazilian Amazonian region over the last four decades have raised questions about potential consequences for local hydrology. Under the hypothesis of a lack of frontier governance, projections of future changes in the Amazon basin suggest that 20–30% or more of this basin could be deforested in the next 40 years. This could trigger a cascade of negative impacts on water resources. In this study, we examined how a future conversion of the forest into pasture would influence streamflow and water balance components by using a conceptual and semi-distributed hydrological model in a large (142,000 km2) forested basin: specifically, the Iriri River basin in the Brazilian Amazon. The results showed that the land use change could substantially alter the water balance components of the originally forested basin. For example, an increase of over 57% in pasture areas increased a simulated annual streamflow by ~6.5% and had a significant impact on evapotranspiration, surface runoff, and percolation. Our findings emphasize the importance of protected areas for conservation strategies in the Brazilian Amazonian region.

Fine-Scale Mapping of Coastal Plant Communities in the Northeastern USA

Salt marshes of the northeastern United States are dynamic landscapes where the tidal flooding regime creates patterns of plant zonation based on differences in elevation, salinity, and local hydrology. These patterns of zonation can change quickly due to both natural and anthropogenic stressors, making tidal marshes vulnerable to degradation and loss. We compared several remote sensing techniques to develop a tool that accurately maps high- and low-marsh zonation to use in management and conservation planning for this ecosystem in the northeast USA. We found that random forests (RF) outperformed other classifier tools when applied to the most recent National Agricultural Imagery Program (NAIP) imagery, NAIP derivatives, and elevation data between coastal Maine and Virginia, USA. We then used RF methods to classify plant zonation within a 500-m buffer around coastal marsh delineated in the National Wetland Inventory. We found mean classification accuracies of 94% for high marsh, 76% for low marsh zones, and 90% overall map accuracy. The detailed output is a 3-m resolution continuous map of tidal marsh vegetation communities and cover classes that can be used in habitat modeling of marsh-obligate species or to monitor changes in marsh plant communities over time.

Microspatial ecotone dynamics at a shifting range limit: plant–soil variation across salt marsh–mangrove interfaces

Ecotone dynamics and shifting range limits can be used to advance our understanding of the ecological implications of future range expansions in response to climate change. In the northern Gulf of Mexico, the salt marsh-mangrove ecotone is an area where range limits and ecotone dynamics can be studied in tandem as recent decreases in winter temperature extremes have allowed for mangrove expansion at the expense of salt marsh. In this study, we assessed aboveground and belowground plant-soil dynamics across the salt marsh-mangrove ecotone quantifying micro-spatial patterns in horizontal extent. Specifically, we studied vegetation and rooting dynamics of large and small trees, the impact of salt marshes (e.g. species and structure) on mangroves, and the influence of vegetation on soil properties along transects from underneath the mangrove canopy into the surrounding salt marsh. Vegetation and rooting dynamics differed in horizontal reach, and there was a positive relationship between mangrove tree height and rooting extent. We found that the horizontal expansion of mangrove roots into salt marsh extended up to eight meters beyond the aboveground boundary. Variation in vegetation structure and local hydrology appear to control mangrove seedling dynamics. Finally, soil carbon density and organic matter did not differ within locations across the salt marsh-mangrove interface. By studying aboveground and belowground variation across the ecotone, we can better predict the ecological effects of continued range expansion in response to climate change.

Impact of Climate Change on Streamflow Hydrology in Headwater Catchments of the Upper Blue Nile Basin, Ethiopia

This study assessed the impact of climate change on water availability and variability in two subbasins in the upper Blue Nile basin of Ethiopia. Downscaled future climate data from HadCM3 of A2 (medium-high) and B2 (medium-low) emission scenarios were compared to the observed climate data for a baseline period (1961–1990). The emission scenario representing the baseline period was used to predict future climate and as input to a hydrologic model to estimate the impact of future climate on the streamflow at three future time horizons: 2020–2045, 2045–2070 and 2070–2100. Results suggest that medium-high emission scenario best represents the local rainfall and temperature pattern. With A2 scenario, daily maximum/minimum temperature will increase throughout the future time horizons. The minimum and maximum temperature will increase by 3.6 °C and 2.4 °C, respectively, towards the end of the 21st century. Consequently, potential evapotranspiration is expected to increase by 7.8%, although trends in annual rainfall do not show statistically meaningful trends between years. A notable seasonality was found in the rainfall pattern, such that dry season rainfall amounts are likely to increase and wet season rainfall to decrease. The hydrological model indicated that the local hydrology of the study watersheds will be significantly influenced by climate change. Overall, at the end of the century, streamflow will increase in both rivers by up to 64% in dry seasons and decrease by 19% in wet seasons.

Late Holocene ice-wedge polygon dynamics in northeastern Siberian coastal lowlands

ABSTRACT Ice-wedge polygons are common features of northeastern Siberian lowland periglacial tundra landscapes. To deduce the formation and alternation of ice-wedge polygons in the Kolyma Delta and in the Indigirka Lowland, we studied shallow cores, up to 1.3 m deep, from polygon center and rim locations. The formation of well-developed low-center polygons with elevated rims and wet centers is shown by the beginning of peat accumulation, increased organic matter contents, and changes in vegetation cover from Poaceae-, Alnus-, and Betula-dominated pollen spectra to dominating Cyperaceae and Botryoccocus presence, and Carex and Drepanocladus revolvens macro-fossils. Tecamoebae data support such a change from wetland to open-water conditions in polygon centers by changes from dominating eurybiontic and sphagnobiontic to hydrobiontic species assemblages. The peat accumulation indicates low-center polygon formation and started between 2380 ± 30 and 1676 ± 32 years before present (BP) in the Kolyma Delta. We recorded an opposite change from open-water to wetland conditions because of rim degradation and consecutive high-center polygon formation in the Indigirka Lowland between 2144 ± 33 and 1632 ± 32 years BP. The late Holocene records of polygon landscape development reveal changes in local hydrology and soil moisture.