Dry Season Flow Research Articles

Riparian canopy expansion in an urban landscape: Multiple drivers of vegetation change along headwater streams near Sacramento, California

Urbanization is thought to decrease riparian tree canopy cover, but this outcome may vary depending on geographic context. We examined changes in land cover and riparian tree canopy near Sacramento, California, a Mediterranean climate region impacted by agriculture before urbanization. We used aerial imagery to quantify changes in land cover and the area, width, and density of riparian tree canopy between 1937 and 2014 for the 85-km2 Arcade Creek watershed. While watershed land cover shifted almost entirely from pasture and crops to urban development, riparian forested area increased by 38 percent. The median width of riparian tree canopy more than doubled, and the density along smaller streams increased significantly (p < 0.0001). We used multiple data sources to examine potential drivers of these changes. Stream gage data and field observations indicated that the formerly intermittent Arcade Creek stream network receives spatially and temporally variable dry-season flow subsidies from urban runoff, but widespread channel incision may limit the impact of subsidies on riparian vegetation. Accordingly, sampling of riparian woody plants showed few hydrophilic species growing along these streams. Instead we found evidence of native oak regeneration and a high density of escaped horticultural species. The increase in riparian forest cover was thus likely due to changes in vegetation management and species composition from land use conversion, possibly augmented by increased dry-season water availability. The changes in canopy cover we quantified stand in contrast to the accepted pattern of riparian forest decline with urbanization, and are expected to affect ecosystem services.

Clarifying regional hydrologic controls of the Marañón River, Peru through rapid assessment to inform system-wide basin planning approaches

We use remote sensing to enhance the interpretation of the first baseline dataset of hydrologic, isotopic and hydrochemical variables spanning 620 km of the upper Marañón River, in Andean Peru, from the steep alpine canyons to the lower lying jungle. Remote, data-scarce river systems are under increased hydropower development pressure to meet rising energy demands. The upstream-downstream river continuum, which serves as a conduit for resource exchange across ecosystems, is at risk, potentially endangering the people, environments, and economies that rely on river resources. The Marañón River, one of the final free-flowing headwater connections between the Andes and the Amazon, is the subject of myriad large-scale hydropower proposals. Due to challenging access, environmental data are scarce in the upper Marañón, limiting our ability to do system-wide river basin planning. We capture key processes and transitions in the context of hydropower development. Two hydrologic regimes control the Marañón dry-season flow: in the higher-elevation upper reaches, a substantial baseflow is fed by groundwater recharged from wet season rains, in contrast to the lower reaches where the mainstem discharge is controlled by rain-fed tributaries that receive rain from lowland Amazon moisture systems. Sustainability of the upper corridor’s dry-season baseflow appears to be more highly connected to the massive natural storage capacity of extensive wetlands in the puna (alpine grasslands) than with cryospheric water inputs. The extent and conservation of puna ecosystems and glacier reservoirs may be interdependent, bringing to bear important conservation questions in the context of changing climate and land use in the region. More generally, this case study demonstrates an efficient combined remote sensing and field observation approach to address data scarcity across regional scales in mountain basins facing imminent rapid change.

Modeling the hydrological impacts of land use/land cover changes in the Andassa watershed, Blue Nile Basin, Ethiopia

Understanding the hydrological response of a watershed to land use/land cover (LULC) changes is imperative for water resources management planning. The objective of this study was to analyze the hydrological impacts of LULC changes in the Andassa watershed for a period of 1985–2015 and to predict the LULC change impact on the hydrological status in year 2045. The hybrid land use classification technique for classifying Landsat images (1985, 2000 and 2015); Cellular-Automata Markov (CA-Markov) for prediction of the 2030 and 2045 LULC states; the Soil and Water Assessment Tool (SWAT) for hydrological modeling were employed in the analyses. In order to isolate the impacts of LULC changes, the LULC maps were used independently while keeping the other SWAT inputs constant. The contribution of each of the LULC classes was examined with the Partial Least Squares Regression (PLSR) model. The results showed that there was a continuous expansion of cultivated land and built-up area, and withdrawing of forest, shrubland and grassland during the 1985–2015 periods, which are expected to continue in the 2030 and 2045 periods. The LULC changes, which had occurred during the period of 1985 to 2015, had increased the annual flow (2.2%), wet seasonal flow (4.6%), surface runoff (9.3%) and water yield (2.4%). Conversely, the observed changes had reduced dry season flow (2.8%), lateral flow (5.7%), groundwater flow (7.8%) and ET (0.3%). The 2030 and 2045 LULC states are expected to further increase the annual and wet season flow, surface runoff and water yield, and reduce dry season flow, groundwater flow, lateral flow and ET. The change in hydrological components is a direct result of the significant transition from the vegetation to non-vegetation cover in the watershed. This suggests an urgent need to regulate the LULC in order to maintain the hydrological balance.

Hydrodynamic characteristics of Wujiangdu Reservoir during the dry season—a case study of a canyon reservoir

With the development of hydropower in the karst area of Southwest China, a series of cascade canyon reservoirs have been formed through the construction of dams. Given that hydrodynamic conditions in canyon reservoirs play a pivotal role in controlling the spatiotemporal distribution of physical and chemical properties of the stored water, hydrodynamic characteristics are of great importance in understanding biogeochemical cycles in those reservoirs. To further this understanding, a field campaign was conducted in the Wujiangdu Reservoir of Guizhou Province. It was found that from the reservoir inlet to the front of the dam, velocity (v) was negatively correlated and had a logarithmic relationship with distance along the ship track (s) under dry-season flow conditions [v = −0.104ln (s) + 0.4756]. Analysis showed that dry-season flow velocity had no significant correlation with water temperature, pH, or dissolved oxygen (DO). However, when velocity decreased to 0.061 m/s, water depth increased abruptly. In addition, DO displayed a sudden drop and the trend in pH changed from increasing to decreasing, while water temperature showed an opposite trend, indicating the existence of a transition zone from the river to the reservoir.

The Effects of Climate Change and Sea Level Rise on Dry Season Flows in Tien River and Hau River

The Effects of Climate Change and Sea Level Rise on Dry Season Flows in Tien River and Hau River

Rebuilding soil hydrological functioning after swidden agriculture in eastern Madagascar

Land-use change due to the widespread practice of swidden agriculture affects the supply of ecosystem services. However, there is comparatively little understanding of how the hydrological functioning of soils, which affects rainfall infiltration and therefore flood risk, dry-season flows and surface erosion, is affected by repeated vegetation clearing and burning, the extent to which this can recover following land abandonment and vegetation regrowth, and whether active restoration speeds up recovery. We used interviews with local land users and indicator plant species to reconstruct the land-use history of 19 different sites in upland eastern Madagascar that represent four different land-use categories: semi-mature forests that were never burnt but were influenced by manual logging until 15–20 years ago; fallows that were actively reforested 6–9 years ago; 2–10year old naturally regenerating fallows; and highly degraded fire-climax grassland sites. Surface- and near-surface (down to 30cm depth) saturated soil hydraulic conductivities (Ksat), as well as the dominant flow pathways for infiltration and percolation were determined for each land-cover type. Surface Ksat in the forest sites was very high (median: 724mmh−1) and infiltration was dominated by flow along roots and other preferential flow pathways (macropores), whereas Ksat in the degraded land was low (median: 45mmh−1) with infiltration being dominated by near-surface matrix flow. The total area of blue-dye stains was inversely correlated to the Ksat. Both surface- and near-surface Ksat had increased significantly after 6–9 years of forest regeneration (median values of 203 and 161mmh−1 for reforestation and natural regeneration, respectively). Additional observations are needed to more fully understand the rates at which soil hydrological functioning can be rebuilt and whether active replanting decreases the time required to restore soil hydrological functioning or not.

A hydrological model for interprovincial water resource planning and management: A case study in the Long Xuyen Quadrangle, Mekong Delta, Vietnam

In this paper we present the results of the development and calibration of a fine-scaled quasi-2D hydrodynamic model (IWRM-LXQ) for the Long Xuyen Quadrangle – an important interprovincial agricultural region in the Vietnamese Mekong Delta. We use the Long Xuyen Quadrangle as a case study to highlight the need for further investment in hydrodynamic modelling at scales relevant to the decisions facing water resource managers and planners in the Vietnamese Mekong Delta. The IWRM-LXQ was calibrated using existing data from a low flood year (2010) and high flood year (2011), including dry season and wet season flows. The model performed well in simulating low flood and high flood events in both dry and wet seasons where good spatial and temporal data exists. However, our study shows that there are data quality issues and key data gaps that need to be addressed before the model can be further refined, validated and then used for decision making. The development of the IWRM-LXQ is timely, as significant investments in land and water resource development and infrastructure are in planning for the Vietnamese Mekong Delta. In order to define the scope of such investments and their feasibility, models such as the IWRM-LXQ are an essential tool to provide objective assessment of investment options and build stakeholder consensus around potentially contentious development decisions.

Assessing the Land Use/Cover Dynamics and its Impact on the Low Flow of Gumara Watershed, Upper Blue Nile Basin, Ethiopia

Land cover and Climate change are very important issues in terms of global context and their responses to environmental and socio-economic drivers. The dynamic of these two factors is currently affecting the environment in unbalanced way including watershed hydrology. In this paper the impact of land use/cover change on stream flow particularly on low flow were evaluated through application of the model Soil and Water Assessment Tool (SWAT) in Gumara watershed, Upper Blue Nile basin Ethiopia. The land use/cover data were obtained from Land Sat image and processed by ERDAS IMAGINE 2010 software. Three land use land cover data; 1973, 1986, and 2013 were prepared and these data were used for base map, model calibration and change study respectively. So, as to evaluate the effect of land use/cover change on low flow of the catchment, the stream flow was simulated by changing 1973 and 2013 LULC but the climate data, which is 1973-1982, was used and it was constant. The low flow of the catchment for these two decades was extracted in simulated flows by Seven Day Sustained (SDS) low flow separation method. The model (SWAT) was calibrated by 1986-1991 climate data and 1986 land use land cover data by using 11 important model parameters selected by sensitivity analysis. The consistency of values of those calibrated parameters was also validated by 1992-1995 climates and with the same land use land cover data. Based on the result, the extreme low flow of Gumara watershed has been decreasing from 0.53 m3/s to 0.43 m3/s which showed decreasing by 0.1 m3/s that is 18.87%. From the overall results of the study, it is possible to conclude that land use land cover change has been influencing the low flow or dry season flow of the catchment. This study has been designed to show how much the land use/cover has been changed and affects the low flow or dry season environmental flow of the catchment. The result has showed some indications that there has to be restoration activities on the land use cover nature of the study area.

Modeling the Impacts of Land Cover Changes on Stream Flow Response in Thiba River Basin in Kenya

Soil and Water Assessment Tool (SWAT) was used to model the impacts of land cover changes on stream flow regime in the Thiba River basin covering a surface area of 1648 km2 in central region of Kenya. The basin is characterized by intensive agricultural activities including the largest rice irrigation scheme in Kenya. A study was undertaken to test the capability of the model in predicting stream flow response under changing land use conditions in a typical tropical river basin. Classified land use maps of 1984, 2004 and 2014 were analyzed to investigate land use changes in the basin. Field based survey, National Irrigation Board (NIB), Kenya Meteorological Department and Water Resources Management Authority (WRMA) provided hydro-meteorological data for the study. The results of the study shows that forest cover in the Thiba River basin has decreased by 18.39 % between 1984 and 2014 while area under rice cultivation increased by 9.38 % in the same period. The SWAT Model results showed that there is a significant relationship between the observed and simulated average monthly stream flows in the Thiba River Basin. The Nash-Sutcliffe Efficiency (NSE) and coefficient of determination (R²) during calibration period (1983-1988) were 0.82 and 0.9, respectively, while for the validation period (1989-1993) they were 0.79 and 0.87, respectively. The average monthly stream flows increased by 6.01 m³/s during the wet season and decreased by 1.92 m³/s during the dry season. The changes in stream flow were attributed to the land cover change and rainfall variability. About 35% of dry season flow and 3% of wet season flow was found to have been directly abstracted from the Thiba River. The study recommends that the basin stakeholders should optimize utilization of abstracted water to avert future catastrophic stream flow fluctuations, possibly flooding during the wet season and low or dry riverbeds during the dry months. The high water demand in the dry months can be met by constructing water storage reservoirs to harvest the high runoff during the wet months. Also, it's important that further research on impact of climate change be conducted to better understand the relationship between catchment hydrology and climate change.

Spatial Distribution of Some Heavy Metals in Sediments from the River Hadejia Catchment, Nigeria

Heavy metals concentration levels was determined using Instrumental Nitrogen Activation Analysis (INAA) is possible using Nigeria Research Reactor-1 (NIRR) which is a Miniature Neutron Source Reactor (MNSR). It is specifically used for the Neutron Activation Analysis (NAA) technique. The selection of sediment sample is because, overtime, the chemical elements precipitate on the sediment bed; therefore the sediment sample will indicate the true nature of the chemical elements present in the river system. River Hadejia is a perennial river, though the dry season flow is from the upstream regulated flow from the Tiga and Bagauda dams. The sediment samples were collected using stratified random sampling technique based on change in land use activity. Samples were collected during dry and wet seasons and analyzed in the laboratory. The results obtained show the presence of chemical contaminants Chromium (Cr), Zinc (Zn), and Europium (Eu) in concentrations above the permissible limits in the Hadejia river system. For example, Chromium (Cr) has mean concentration of 432.86 mg/l as against the permissible limit for both WHO, (2011) and NSDWQ, (2007) of 0.05mg/l. Anthropogenic and natural geology of the area are the key determinants of the presence of these chemical elements in the area. It is recommended among others that there is need for routing the actual sources of these contaminants in our river catchment areas.

Implications of decadal to century scale glacio‐hydrological change for water resources of the Hood River basin, OR, USA

AbstractIn glacier‐fed rivers, melting of glacier ice sustains streamflow during the driest times of the year, especially during drought years. Anthropogenic and ecologic systems that rely on this glacial buffering of low flows are vulnerable to glacier recession as temperatures rise. We demonstrate the evolution of glacier melt contribution in watershed hydrology over the course of a 184‐year period from 1916 to 2099 through the application of a coupled hydrological and glacier dynamics model to the Hood River basin in Northwest Oregon, USA. We performed continuous simulations of glaciological processes (mass accumulation and ablation, lateral flow of ice and heat conduction through supra‐glacial debris), which are directly linked with seasonal snow dynamics as well as other key hydrologic processes (e.g. evapotranspiration and subsurface flow). Our simulations show that historically, the contribution of glacier melt to basin water supply was up to 79% at upland water management locations. We also show that supraglacial debris cover on the Hood River glaciers modulates the rate of glacier recession and progression of dry season flow at upland stream locations with debris‐covered glaciers. Our model results indicate that dry season (July to September) discharge sourced from glacier melt started to decline early in the 21st century following glacier recession that started early in the 20th century. Changes in climate over the course of the current century will lead to 14–63% (18–78%) reductions in dry season discharge across the basin for IPCC emission pathway RCP4.5 (RCP8.5). The largest losses will be at upland drainage locations of water diversions that were dominated historically by glacier melt and seasonal snowmelt. The contribution of glacier melt varies greatly not only in space but also in time. It displays a strong decadal scale fluctuations that are super‐imposed on the effects of a long‐term climatic warming trend. This decadal variability results in reversals in trends in glacier melt, which underscore the importance of long‐time series of glacio‐hydrologic analyses for evaluating the hydrological response to glacier recession. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Patterns and Implications of Hydrologic Regime Change in Chongwe River, Zambia

Conflicts regarding water use have emerged in some small irrigation dominated peri-urban catchments in Zambia; Chongwe being one such catchment. Despite these conflicts suggesting a change in hydrologic regime, the nature of the changes and their drivers has not been adequately investigated. The Mann Kendall trend test and Flow Duration Curves were used to investigate changes in hydro-climatic time series data in Chongwe upper catchment for the period 1955-2006. Although the results reviewed a significant upward trend in temperature at 0.05 significance level, there is no significant trend in rainfall. Annual and seasonal runoff at the upstream located Ngwerere weir reviewed significant upward trends at 0.05 significance level. This increased runoff which is attributed to sewer water discharge and increased imperviousness is abstracted for agricultural activities upstream. In this regard, results reviewed no significant trend in runoff at the outlet gauging station (Chongwe 5025). However, analysis of the Flow Duration Curves at this outlet gauging station indicated an increase in wet season flows and a reduction in dry season flows for the 1990-2006 period. These results suggest that human activities in the upstream parts of the catchments could be the major contributing factors to the changes in flow regime, hence the ensuing upstream vs downstream water use conflicts. However, there is still excess runoff in the wet season that could be harvested by downstream water users in order to offset the deficit in downstream dry season flows.

Exploitable Potential, Theoretical Potential, Technical Potential, Storage Potential and Impediments to Development of the Potential: The Nepalese Perspective

Exploitable potential is an ultimate derivable of theoretical potential, technical potential and/or storage potential. A number of hurdles come across when a potential site has to be exploited, thus, all theoretically and/or technically available potential cannot actually be developed/ exploited. Nepal is not an exception in this respect. Exploitation of run-of-river schemes has much less hurdle in comparison with storage development. The storage development, particularly the larger scale development, has even international implications, because the benefits of such development spread far beyond the national boundary. In the Nepalese case the downstream country, particularly India, is reluctant to recognize the downstream flow regulation benefits arising from flood-control and dry season flow augmentation. As such the current focus of exploitation of Nepalese hydro-potential should be on run-of-river type development and smaller size storage developments which can easily be materialized without much hurdle, but in a coordinated and well scheduled manner in a way not to hamper the larger storage development at the opportune future dates.HYDRO Nepal JournalJournal of Water, Energy and EnvironmentIssue: 19Page:1-5

Morphological response of the saltmarsh habitats of the Guadiana estuary due to flow regulation and sea-level rise

In the context of rapid sea-level rise in the 21st century, the reduction of fluvial sediment supply due to the regulation of river discharge represents a major challenge for the management of estuarine ecosystems. Therefore, the present study aims to assess the cumulative impacts of the reduction of river discharge and projected sea-level rise on the morphological evolution of the Guadiana estuary during the 21st century. The assessment was based on a set of analytical solutions to simplified equations of tidal wave propagation in shallow waters and empirical knowledge of the system. As methods applied to estimate environmental flows do not take into consideration the fluvial discharge required to maintain saltmarsh habitats and the impact of sea-level rise, simulations were carried out for ten cases in terms of base river flow and sea-level rise so as to understand their sensitivity on the deepening of saltmarsh platforms.Results suggest saltmarsh habitats may not be affected severely in response to lower limit scenarios of sea-level rise and sedimentation. A similar behaviour can be expected even due to the upper limit scenarios until 2050, but with a significant submergence afterwards. In the case of the upper limit scenarios under scrutiny, there was a net erosion of sediment from the estuary. Multiplications of amplitudes of the base flow function by factors 1.5, 2, and 5 result in reduction of the estimated net eroded sediment volume by 25, 40, and 80%, respectively, with respect to the net eroded volume for observed river discharge. The results also indicate that defining the minimum environmental flow as a percentage of dry season flow (as done presently) should be updated to include the full spectrum of natural flows, incorporating temporal variability to better anticipate scenarios of sea-level rise during this century. As permanent submergence of intertidal habitats can be significant after 2050, due to the projected 79 cm rise of sea-level by the year 2100, a multi-dimensional approach should be adopted to mitigate the consequences of sea-level rise and strong flow regulations on the ecosystem of the Guadiana Estuary.

Hydrologic Impact Evaluation of Land Use and Land Cover Change in Palico Watershed, Batangas, Philippines Using the SWAT Model

Information on the relationship between hydrologic response and land use and land cover change (LULC) is vital for proper management of water resources and land use planning. This study aimed to evaluate the impact of LULC on the hydrologic characteristics of Palico watershed in Batangas, Philippines using the Soil and Water Assessment Tool (SWAT) model. Model inputs used were the 1989 and 2013 LULC maps and climatological and hydrologic data. Good agreement was obtained between simulated and observed streamflow values during model calibration (NSE=0.84 &amp; R2=0.86), and validation (NSE=0.61 &amp; R2=0.68). For the entire watershed, reduction in forest cover and rangeland resulted to an increase in surface runoff and decreases in baseflow or dry season flow and groundwater recharge. LULC changes affected the water quantity and timing of occurrence. Subbasin with 22% increase in forest cover and rangeland increased the baseflow by 1% to 15% and reduced the streamflow by 1% to 17% during the rainy months. Another subbasin with 54% forest loss resulted to more pronounced rainfall-runoff response with 11% to 17% decrease in baseflow and 4% to 24% increase in streamflow during rainy months. Finding the balance between these two opposite LULC change scenarios is crucial for the attainment of water security and sustainability in the watershed and in the areas it serves.

Effect of Proposed Large Dams on Water Flows and Hydropower Production in the Sekong, Sesan and Srepok Rivers of the Mekong Basin

Water flow patterns in the Mekong are changing because of on-going rapid hydropower development triggered by economic growth. Of immediate concern are the current and proposed hydropower dams in the transboundary Srepok, Sesan and Srekong (3S) Rivers, which contribute up to 20% of the Mekong's annual flows, have a large potential for energy production and provide critical ecosystem services to the downstream Tonle Sap Lake and Mekong Delta. The objective of this paper is to determine how the operation of the proposed largest individual dams and cascade dam schemes in the 3S Rivers will affect flow regimes and energy production. Daily flows were simulated over 20 years using the Soil and Water Assessment Tool and HEC-ResSim models for a range of dam development and operations scenarios. The development of all dams in the 3S basin under an operation scheme to maximize individual electricity production results in an average 98% increase in dry season flows at the 3S outlet. Over 55% of dry season flows changes are caused by seven proposed large dams, with the Lower Srepok 3 project causing the highest impact. The seven large dams will generate 33.0 GWh/day with a water volume of 17 679 x 106 m3, compared with the current and definite future dams generating 73.2 GWh/day with a much lower volume of 6616 x 106 m3. When a cascade of dams are operational, downstream dams with small reservoirs will produce more energy. However, the marginal increase in energy production from the development of additional dams in the 3S basin will decline rapidly relative to the required water storage increase,. Strategic decision-making on the future of each large proposed dam in the 3S basin needs to be considered by local governments after understanding cumulative operation effects and with further consideration to the potential impact on downstream ecosystem productivity and livelihoods. Copyright © 2016 John Wiley & Sons, Ltd.

Climatic risks and impacts in South Asia: extremes of water scarcity and excess

This paper reviews the current knowledge of climatic risks and impacts in South Asia associated with anthropogenic warming levels of 1.5–4 °C above pre-industrial values in the twenty-first century. It is based on the World Bank Report “Turn Down the Heat, Climate Extremes, Regional Impacts and the Case for Resilience” (2013b) . Many of the climate change impacts in the region, which appear quite severe even with relatively modest warming of 1.5–2 °C, pose significant hazards to development. For example, increased monsoon variability and loss or glacial meltwater will likely confront populations with ongoing and multiple challenges. The result is a significant risk to stable and reliable water resources for the region, with increases in peak flows potentially causing floods and dry season flow reductions threatening agriculture. Irrespective of the anticipated economic development and growth, climate projections indicate that large parts of South Asia’s growing population and especially the poor are likely to remain highly vulnerable to climate change.

Dry season streamflow persistence in seasonal climates

AbstractSeasonally dry ecosystems exhibit periods of high water availability followed by extended intervals during which rainfall is negligible and streamflows decline. Eventually, such declining flows will fall below the minimum values required to support ecosystem functions or services. The time at which dry season flows drop below these minimum values (Q*), relative to the start of the dry season, is termed the “persistence time” ( ). The persistence time determines how long seasonal streams can support various human or ecological functions during the dry season. In this study, we extended recent work in the stochastic hydrology of seasonally dry climates to develop an analytical model for the probability distribution function (PDF) of the persistence time. The proposed model accurately captures the mean of the persistence time distribution, but underestimates its variance. We demonstrate that this underestimation arises in part due to correlation between the parameters used to describe the dry season recession, but that this correlation can be removed by rescaling the flow variables. The mean persistence time predictions form one example of the broader class of streamflow statistics known as crossing properties, which could feasibly be combined with simple ecological models to form a basis for rapid risk assessment under different climate or management scenarios.

Assessing the effects of land cover and future climate conditions on the provision of hydrological services in a medium-sized watershed of Portugal

The separated and combined effects of land-cover scenarios and future climate on the provision of hydrological services were evaluated in Vez watershed, northern Portugal. Soil and Water Assessment Tool was calibrated against daily discharge, sediments and nitrates, with good agreements between model predictions and field observations. Four hypothetical land-cover scenarios were applied under current climate conditions (eucalyptus/pine, oak, agriculture/vine and low vegetation). A statistical downscaling of four General Circulation Models, bias-corrected with ground observations, was carried out for 2021-2040 and 2041-2060, using representative concentration pathway 4.5 scenario. Also, the combined effects of future climate conditions were evaluated under eucalyptus/pine and agriculture/vine scenario. Results for land cover revealed that eucalyptus/pine scenario reduced by 7% the annual water quantity and up to 17% in the summer period. Although climate change has only a modest effect on the reduction of the total annual discharge (-7%), the effect on the water levels during summer was more pronounced, between -15% and -38%. This study shows that climate change can affect the provision of hydrological services by reducing dry season flows and by increasing flood risks during the wet months. Regarding the combined effects, future climate may reduce the low flows, which can be aggravated with eucalyptus/pine scenario. In turn, peak flows and soil erosion can be offset. Future climate may increase soil erosion and nitrate concentration, which can be aggravated with agriculture scenario. Results moreover emphasize the need to consider both climate and land-cover impacts in adaptation and land management options at the watershed scale.

From past patterns to future potential: using historical ecology to inform river restoration on an intermittent California river

Effective river restoration requires understanding a system’s potential to support desired functions. This can be challenging to discern in the modern landscape, where natural complexity and heterogeneity are often heavily suppressed or modified. Historical analysis is therefore a valuable tool to provide the long-term perspective on riverine patterns, processes, and ecosystem change needed to set appropriate environmental management goals and strategies. In this study, we reconstructed historical (early 1800s) riparian conditions, river corridor extent, and dry-season flow on the lower Santa Clara River in southern California, with the goal of using this enhanced understanding to inform restoration and management activities. Hundreds of cartographic, textual, and visual accounts were integrated into a GIS database of historical river characteristics. We found that the river was characterized by an extremely broad river corridor and a diverse mosaic of riparian communities that varied by reach, from extensive (>100 ha) willow-cottonwood forests to xeric scrublands. Reach-scale ecological heterogeneity was linked to local variations in dry-season water availability, which was in turn underpinned by regional geophysical controls on groundwater and surface flow. Although human actions have greatly impacted the river’s extent, baseflow hydrology, and riparian habitats, many ecological attributes persist in more limited form, in large part facilitated by these fundamental hydrogeological controls. By drawing on a heretofore untapped dataset of spatially explicit and long-term environmental data, these findings improve our understanding of the river’s historical and current conditions and allow the derivation of reach-differentiated restoration and management opportunities that take advantage of local potential.