Hydroclimatic Variability Research Articles

Hydrologic recovery after wildfire: A framework of approaches, metrics, criteria, trajectories, and timescales

Abstract Deviations in hydrologic processes due to wildfire can alter streamflows across the hydrograph, spanning peak flows to low flows. Fire-enhanced changes in hydrologic processes, including infiltration, interception, and evapotranspiration, and the resulting streamflow responses can affect water supplies, through effects on the quantity, quality, and timing of water availability. Post-fire shifts in hydrologic processes can also alter the timing and magnitude of floods and debris flows. The duration of hydrologic deviations from a pre-fire condition or function, sometimes termed hydrologic recovery, is a critical concern for land, water, and emergency managers. We reviewed and summarized terminology and approaches for defining and assessing hydrologic recovery after wildfire, focusing on statistical and functional definitions. We critically examined advantages and drawbacks of current recovery assessment methods, outline challenges to determining recovery, and call attention to selected opportunities for advancement of post-fire hydrologic recovery assessment. Selected challenges included hydroclimatic variability, post-fire land management, and spatial and temporal variability. The most promising opportunities for advancing assessment of hydrologic recovery include: (1) combining statistical and functional recovery approaches, (2) using a greater diversity of post-fire observations complemented with hydrologic modeling, and (3) defining optimal assemblages of recovery metrics and criteria for common hydrologic concerns and regions.

Representation of Atmospheric Water Budget and Uncertainty Quantification of Future Changes in CMIP6 for the Seven U.S. National Climate Assessment Regions

Abstract Observation-based climate model evaluation and future projections help policymakers in developing action plans for efficient management of water resources and mitigation of the impacts of hazardous extremes. Apart from this socioeconomic importance, the scientific value cannot be overstated, especially in light of the upcoming Fifth U.S. National Climate Assessment (NCA) report. In this study, we evaluate the realism of hydroclimate variability in the historical simulations of a suite of coupled general circulation models (CGCMs) participating in the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). Our results demonstrate systematic biases in the simulated seasonal precipitation—most prominently, wet bias over the mountainous western United States in winter, and dry bias over the U.S. central plains in summer. A distinctive feature of this work is our focus on the examination of the atmospheric water budget, in particular the relative importance of remote and local contributions—convergence of moisture fluxes and local land surface processes (evapotranspiration) respectively—in helping produce precipitation. This diagnosis reveals that the leading contribution of the remote influence in winter is overestimated by the CMIP6 multimodel mean (MMM), whereas the local influence, which is more influential in summer, is underestimated. Our results aid in understanding the drivers of seasonal precipitation over the United States, where precipitation will likely increase by the end of the century but with significant model disagreement for the summer and fall. In support of ongoing NCA efforts, our study aims to contribute a comprehensive, regional-level analysis of the moisture budget and emphasizes the importance of realistically simulating its major components in CGCMs.

Effect of hydro-climate variation on biofilm dynamics and its impact in intertidal environments

Abstract. Shallow tidal environments are very productive ecosystems but are sensitive to environmental changes and sea level rise. Bio-morphodynamic control of these environments is therefore a crucial consideration; however, the effect of small-scale biological activity on large-scale cohesive sediment dynamics like tidal basins and estuaries is still largely unquantified. This study advances our understanding by assessing the influence of biotic and abiotic factors on biologically cohesive sediment transport and morphology. An idealised benthic biofilm model is incorporated in a 1D morphodynamic model of tide-dominated channels. This study investigates the effect of a range of environmental and biological conditions on biofilm growth and their feedback on the morphological evolution of the entire intertidal channel. By carrying out a sensitivity analysis of the bio-morphodynamic model, parameters like (i) hydrodynamic disturbances, (ii) seasonality, (iii) biofilm growth rate, (iv) temperature variation and (v) bio-cohesivity of the sediment are systematically changed. Results reveal that key parameters such as growth rate and temperature strongly influence the development of biofilm and are key determinants of equilibrium biofilm configuration and development under a range of disturbance periodicities and intensities. Long-term simulations of intertidal channel development demonstrate that the hydrodynamic disturbances induced by tides play a key role in shaping the morphology of the bed and that the presence of surface biofilm increases the time to reach morphological equilibrium. In locations characterised by low hydrodynamic forces, the biofilm grows and stabilises the bed, inhibiting the transport of coarse sediment (medium and fine sand). These findings suggest biofilm presence in channel beds results in intertidal channels that have significantly different characteristics in terms of morphology and stratigraphy compared abiotic sediments. It is concluded that inclusion of bio-cohesion in morphodynamic models is essential to predict estuary development and mitigate coastal erosion.

Paleo‐denudation rates suggest variations in runoff drove aggradation during last glacial cycle, Crete, Greece

AbstractFluvial aggradation and incision are often linked to Quaternary climate cycles, but it usually remains unclear whether variations in runoff or sediment supply or both drive channel response to climate variability. Here we quantify sediment supply with paleo‐denudation rates and provide geochronological constraints on aggradation and incision from the Sfakia and Elafonisi alluvial‐fan sequences in Crete, Greece. We report seven optically stimulated luminescence and ten radiocarbon ages, eight10Be and eight36Cl denudation rates from modern channel and terrace sediments. For five samples,10Be and36Cl were measured on the same sample by measuring10Be on chert and36Cl on calcite. Results indicate relatively steady denudation rates throughout the past 80 kyr, but the aggradation and incision history indicates a link with climate shifts. At the Elafonisi fan, we identify four periods of aggradation coinciding with Marine Isotope Stages (MIS) 2, 4, 5a/b, and likely 6, and three periods of incision coinciding with MIS 1, 3, and likely 5e. At the Sfakia fan, rapid aggradation occurred during MIS 2 and 4, followed by incision during MIS 1. Nearby climate and vegetation records show that MIS 2, 4, and 6 stadials were characterized by cold and dry climates with sparse vegetation, whereas forest cover and more humid conditions prevailed during MIS 1, 3, and 5. Our data thus suggest that past changes in climate had little effect on landscape‐wide denudation rates but exerted a strong control on the aggradation–incision behaviour of alluvial channels on Crete. During glacial stages, we attribute aggradation to hillslope sediment release promoted by reduced vegetation cover and decreased runoff; conversely, incision occurred during relatively warm and wet stages due to increased runoff. In this landscape, past hydroclimate variations outcompeted changes in sediment supply as the primary driver of alluvial deposition and incision.

The influence of climate change on freshwater availability in the Sokoto Rima River Basin, Northwestern Nigeria.

This research entailed the acquisition of long-term (1980-2020) meteorological data (rainfall, temperature, and runoff) which was used to compute the values for the mean annual, monthly, and seasonal hydro-climate variables to establish their trend and behavior. To substantiate if the patterns of runoff are in any way due to the changing climate, the meteorological data were subjected to non-parametric tests-Mann-Kendall (MK), Sen's slope estimator, Kendall tau, and partial correlation. MK trend test for runoff, rainfall, and temperature (on an annual and seasonal basis) revealed significant trends on an annual scale. Nevertheless, rainfall data did not exhibit any, observable trend on a seasonal scale. On both annual and seasonal scales, temperature values showed increasing trends. In the entire period considered (1980-2020), runoff also exhibited a remarkable increase in trend. Sen's estimator values ranged from - 0.04 to 3.23. The results of the Kendall tau correlation showed that runoff is positively correlated to rainfall (tau = 0.222), with a high confidence level (95%). Again, the partial correlation analysis of runoff and climatic variables for annual and seasonal timescale, results show that the runoff is significantly (rxy.z = 0.315) affected by both rainfall and temperature. It is therefore recommended that future research should utilize robust input-output models to determine the amount of water stress in the basin. As a sustainable management approach, artificial surface water reservoirs should be constructed to complement the available water from the Sokoto-Rima river and alleviate the water stress experienced by the population.

The hydroclimate niche: A tool for predicting and managing riparian plant community responses to streamflow seasonality

AbstractHabitat suitability is a consequence of interacting environmental factors. In riparian ecosystems, suitable plant habitat is influenced by interactions between stream hydrology and climate, hereafter referred to as “hydroclimate”. We tested the hypothesis that hydroclimate variables would improve the fit of ecological niche models for a suite of riparian species using occurrence data from the western United States. We focus on the climate conditions (temperature, precipitation and vapor pressure deficit) during the months of lowest and highest streamflow as integrative hydroclimate metrics of resource and stress levels. We found that the inclusion of hydroclimate variables improved model fit for all species in the western USA dataset. We then tested the utility of the improved habitat suitability models by projecting them onto a regulated segment of the Colorado River to assess potential impacts of streamflow seasonality on vegetation metrics of management concern. Species frequency derived from independent survey data in the Colorado River segment was significantly higher for species with predicted suitable habitat than for species without predicted suitable habitat. Under different simulated hydrographs for the Colorado River, overall species richness was predicted to be greatest with peak streamflows during summer, and native‐to‐non‐native species ratios were predicted to be greatest with lowest streamflows in winter. Summer high flows were particularly associated with higher predicted habitat suitability for species that have increased in cover over recent decades (e.g., Pluchea sericea, Baccharis species). We conclude that hydroclimate covariates can be useful tools for predicting how riparian vegetation communities respond to changes in the seasonal timing of low and high streamflows.

Multi-phased Asian hydroclimate variability during Heinrich Stadial 5

Multi-phased Asian hydroclimate variability during Heinrich Stadial 5

Spatial pattern of orbital-to millennial-scale East Asian stalagmite δ18O variations during MIS 3

The Asian hydroclimate variability during the early and middle Marine Isotope Stage (MIS) 3 was reconstructed from a high-resolution stalagmite δ18O record from Qixing Cave in southern China, which exhibited an extraordinarily strong precessional cycle. When compared with other cave records (mostly) from East Asia, covering a latitudinal transect from 23° to 38°N, it can be found that the magnitude of precessional-scale stalagmite δ18O variations decreases when the latitude increases, approximately from 3‰ to 1‰. In contrast, the amplitude of Heinrich stadials (HSs) in these stalagmite δ18O records enhances with increasing latitudes, from 1‰ to 2‰, reflecting an alleviated effect of high-latitude climate changes on the low-latitude hydroclimate, or a relative contribution from Westerlies-borne and near-sourced 18O-enriched moisture at northern China. In southern China, orbital-scale changes in stalagmite δ18O closely match variations of the atmospheric CH4 concentration and δ18O of the atmospheric O2, suggesting a coherent response of low-latitude ecological and hydrological processes. In addition, a weaker precessional cycle in northern China is possibly related to the relative supply of near-sourced moisture source, where the Westerly wind can exert a substantial role. Therefore, precessional to millennial-scale changes in East Asian stalagmite δ18O records could be further modulated by local processes, rendering them a spatially contrasting trait. A pervasive imprint of muted precessional rainfall changes in loess records from northern China suggests a regionally distinct rhythm of moisture availability, in agreement with the stalagmite records from higher latitudes.

Deciphering human influence on annual maximum flood extent at the global level

Human actions are increasingly altering most river basins worldwide, resulting in changes in hydrological processes and extreme events. Yet, global patterns of changes between seasonal surface water and urbanization remain largely unknown. Here we perform a worldwide analysis of 106 large river basins and uncover global trends of annual maximum flood extent and artificial impervious area, as proxy of urbanization, over the past three decades. We explore their relationships with hydroclimatic variability, expressed as rainfall and snowmelt, and find that hydroclimatic variability alone cannot explain changes in annual maximum flood extent in 75% of the analyzed major river basins worldwide. Considering rainfall and urban area together can explain changes in the annual maximum flood extent in 57% of the basins. Our study emphasizes the importance of understanding the global impacts of human presence on changes in seasonal water dynamics.

Prediction of leptospirosis outbreaks by hydroclimatic covariates: a comparative study of statistical models.

Leptospirosis, the infectious disease caused by a spirochete bacteria, is a major public health problem worldwide. In Argentina, some regions have climatic and geographical characteristics that favor the habitat of bacteria of the Leptospira genus, whose survival strongly depends on climatic factors, enhanced by climate change, which increase the problems associated with people’s health. In order to have a method to predict leptospirosis cases, in this paper, five time series forecasting methods are compared: two parametric (autoregressive integrated moving average and an alternative one that allows covariates, ARIMA and ARIMAX, respectively), two nonparametric (Nadaraya-Watson Kernel estimator, one and two kernels versions, NW-1 K and NW-2 K), and one semiparametric (semi-functional partial linear regression, SFPLR) method. For this, the number of cases of leptospirosis registered from 2009 to 2020 in three important cities of northeastern Argentina is used, as well as hydroclimatic covariates related to the presence of cases. According to the obtained results, there is no method that improves considerably the rest and can be recommended as a unique tool for leptospirosis prediction. However, in general, the NW-2 K method gets a better performance. This work, in addition to using a long-term high-quality time series, enriches the area of applications of statistical models to epidemiological leptospirosis data by the incorporation of hydroclimatic variables, and it is recommended directing further efforts in this line of research, under the context of current climate change.

Google Earth Engine as Multi-Sensor Open-Source Tool for Monitoring Stream Flow in the Transboundary River Basin: Doosti River Dam

Understanding the effects of global change and human activities on water supplies depends greatly on surface water dynamics. A comprehensive examination of the hydroclimatic variations at the transboundary level is essential for the development of any adaptation or mitigation plans to deal with the negative effects of climate change. This research paper examines the hydroclimatic factors that contribute to the desiccation of the Doosti Dam’s basin in the transboundary area using multisensor satellite data from the Google Earth Engine (GEE) platform. The Mann–Kendall and Sens slope estimator test was applied to the satellite datasets to analyse the spatial and temporal variation of the hydroclimate variables and their trend over the transboundary area for 18 years from 2004 to 2021 (as the dam began operating in 2005). Statistical analysis results showed decreasing trends in temperature and an increase in rainfall with respect to station-observed available data. Evapotranspiration and irrigated area development followed the increasing pattern and a slight decrease in snow cover. The results confirmed a large expansion of the irrigated area, especially during the winter growing season. The increase in irrigated cultivated areas during both winter and summer seasons is possibly the main reason for the diversion of water to meet the irrigation requirements of the developed agriculture areas. The approach followed in this study could be applied to any location around the globe to evaluate the hydrological conditions and spatiotemporal changes in response to climate change, trend analysis and human activities.

Serial droughts and loss of hydrologic resilience in a subtropical basin: The case of water inflow into the Cantareira reservoir system in Brazil during 2013–2021

Study regionSoutheastern Brazil, with emphasis on the Jaguari River basin, the main tributary of the Cantareira system. Study focusWe examined the basin hydroclimate variability, especially along the historical meteorological droughts between 2013 and 2021, and the hydrologic response to negative disturbances in rainfall. Field and satellite measurements of rainfall, flow, soil moisture, and water storage were used to assess the hydroclimate variability and to validate the hydrological model. Our hypothesis is that a good model performance on these validated variables improve our confidence in the representation of aquifer storage and recharge. We also estimated the long-term elasticity of flow to precipitation using the entire analysis period (27 years), and compared to the elasticity in along the serial droughts from 2017 to 2021. New hydrological insights for the regionResults show that the serial meteorological droughts were very likely unprecedented in the last 70 years, leading to hydrologic impacts over regional scale. We estimated a decrease of 6.4 mm y-1 in the soil moisture and a reduction of 26% in the aquifer recharge in the last 5 years of serial droughts. In the same period, the elasticity of flow to precipitation was 3.1, which greatly exceeded the long-term value of 2.0. This greater hydrologic sensitivity in the elasticity may represent that the resilience of the surface hydrologic system was transiently lost.

Elevation dependence of projected hydro-climatic change in eastern Siberia

Over the last several decades, eastern Siberia has experienced some of the largest temperature increases worldwide. We use the RCP8.5 simulation of the Community Climate System Model version 4 to examine how projected monthly changes in temperature and hydro-climatic variables in eastern Siberia depend on latitude and elevation. Temperature increases are largest at the highest latitudes in winter and late fall and are smaller at higher elevations. For precipitation and snowfall, there is a latitudinal dependence in autumn and spring, with precipitation, snowfall, and snow depth mostly increasing between 60 and 70° N. Although snow cover extent (SCE) decreases almost everywhere, the largest changes occur during the transition seasons which we define as spring and autumn, and the timing of the changes depends on latitude, elevation, and the specific month within seasons. The decreases in SCE are larger at lower latitudes and lower elevations in April and November and larger at higher elevations and higher latitudes in June and September. For the highest latitudes, snow depth actually increases, and increases more at higher elevations. These projections are generally consistent with those of four other climate models. For precipitation, all models project increases in non-summer seasons, but they are not consistent with respect to the direction of the elevation dependence of precipitation. We discuss the complex interactions among the projected changes in all the variables.

Features of Radial Growth Rate of Trees in Agro-Pastoral Transition Zone, Northern China

The Vaganov–Shashkin process-based model was used to explore the variation characteristic of the radial growth rate of Pinus tabulaeformis in the agro-pastoral transition zone in northern China. The tree-ring width chronologies of the four sampling sites were significantly positively correlated with the simulated series (p < 0.01), and the simulated onset and end dates of tree radial growth indicated that April to October was the main growing season. Temperature affects the radial growth rate of tree stems at the start and end of the growing season, while soil moisture availability affects the radial growth rate in the main growing season. Despite the differences in amplitude, the integral growth rate showed a bimodal pattern, which to some extent responded to the hydrothermal configuration of the East Asian summer monsoon climate. Compared with the peak changes in the summer monsoon fringe area in Northwest China, the highest peak of the integral growth rate in this study area appeared around August in the late growing season, reflecting the adaptability of trees to the local climatic environment. The average values of the integral growth rate and rate due to soil moisture, inferred from extreme wide-ring and narrow-ring years, were significantly different (p < 0.01), while the average growth rates due to temperature were not significant (p > 0.05). The analysis results indicate that moisture availability is a key limiting factor for the radial growth of Pinus tabulaeformis. Our study provides valuable knowledge about the growth processes of the main tree species related to the hydroclimatic variables in northern China and offers a new perspective on mitigating the adverse effects of a warmer climate on the forest in the semi-arid region in the future.

Hydrometeorological Processes and Moisture Sources in the Northeastern Tibetan Plateau: Insights from a 7-Yr Study on Precipitation Isotopes

Abstract The northeastern Tibetan Plateau is located in a climatic junction, which is considered an ideal region to explore the interactions between the summer monsoons and the westerly circulation patterns. However, to date, the needed long-term precipitation-based isotopic dataset is too limited to predict the interactions and patterns. This paper presents an evaluation of hydrometeorological processes and climate dynamics in the northeastern Tibetan Plateau based on a 7-yr precipitation isotope dataset covering the summer monsoon periods from 2012 to 2018. Results illustrated remarkable seasonal isotopic variability, characterized by lower δ18O and δ2H values in June with an average of −10‰ and −66.7‰, respectively. Higher δ18O and δ2H values in July averaged −6.7‰ and −39.5‰, respectively. This clear isotopic variability is largely related to seasonal changes of moisture sources and hydrometeorological processes. These precipitation isotopic values were primarily determined by the amount of precipitation, relative humidity, and convective activity, but showed no correlation with air temperature. Backward trajectory model results showed that Xinjiang, northern China, the Arctic, central Asia, and the South China Sea (SCS) were the primary sources of precipitation for the study site with varying seasonal contributions. The maritime moisture source of the SCS primarily resulted in the lowest precipitation δ18O values during the prevailing summer monsoon, which is mainly as a result of the strong convective activity and rainout processes along the air trajectory. The higher average deuterium excess (d-excess) value of precipitation in September indicated continental sources from central Asia (e.g., 75.4%) as land vapor recycling increases d-excess concentration in the atmosphere. These findings provide further insights into the main factors of precipitation isotopic variability related to atmospheric processes along the trajectory and the relevant factors in the monsoon regions. Significance Statement Recently, scientists and policy makers have become aware that Tibetan hydroclimate variability provides evidence of changes in regional and global circulation patterns that may result in the intensification of climate-driven extremes. However, these studies largely depend on crucial paleoclimate records of past precipitation isotopes in monsoon regions, which contain great uncertainties because of the complex relationship between climatic variability and precipitation isotopes. This study first presented a 7-yr isotopic dataset to understand the hydrological processes and climate dynamics controlling the isotopic variability in the northeastern Tibetan Plateau. The findings reveal important factors on the isotopic variability associated with atmospheric processes and their key climatic variables, which can enhance our interpretation of the paleoclimate records in monsoon regions.

Scrutinizing the Intermittency of Renewable Energy in a Long-Term Planning Model via Combining Direct Integration and Soft-Linking Methods for Colombia’s Power System

The large-scale integration of variable renewable energy sources into the energy system presents techno–economic challenges. Long–term energy system optimization models fail to adequately capture these challenges because of the low temporal resolution of these tools. This limitation has often been addressed either by direct improvements within the long–term models or by coupling them to higher resolution power system models. In this study, a combined approach is proposed to capitalize on the advantages and overcome the disadvantages of both methods. First, the temporal resolution of an energy model was enhanced by approximating the joint probability of the electricity load and the supply of intermittent sources. Second, the projected electricity mix was simulated by a power model at an hourly resolution. This framework was used to analyze mid–century deep decarbonization trajectories for Colombia, subject to future uncertainties of hydroclimatic variability and the development of the bioeconomy. The direct integration method is found to consistently reduce the overestimation of the feasible penetration of VRES. However, its impact is marginal because of its inability to assess the short–term operation of the power system in detail. When combined with the soft–linking method, the reliable operation of the power system is shown to incur an additional overhead of 12–17% investment in flexible generation capacity, 2–5% of the annual energy system cost, and a 15–27% shortfall in achieving the aspired GHG mitigation target. The results obtained by combining both methods are found to be closer to the global optimum solution than using either of these methods individually.

Variable Response in Alpine Tree-Ring Stable Isotopes Following Volcanic Eruptions in the Tropics and Iceland

The importance of the stable isotopes in tree rings for the study of the climate variations caused by volcanic eruptions is still unclear. We studied δ18O, δD, δ13C stable isotopes of larch and cembran pine cellulose around four major eruptions with annual resolution, along with a superposed epoch analysis of 34 eruptions with 5-year resolution. Initial analysis of the tropical Tambora (1815 CE) and Samalas (1257 CE) eruptions showed a post-eruption decrease in δ18O values attributed to post-volcanic cooling and increased summer precipitation in Southern Europe, as documented by observations and climate simulations. The post-volcanic cooling was captured by the δD of speleothem fluid inclusion. The δ18O decrease was also observed in the analysis of 34 major tropical eruptions over the last 2000 years. In contrast, the eruptions of c. 750, 756, and 764 CE attributed to Icelandic volcanoes left no significant responses in the cellulose isotopes. Further analysis of all major Icelandic eruptions in the last 2000 years showed no consistent isotopic fingerprints, with the exception of lower post-volcanic δ13C values in larch. In summary, the δ18O values of cellulose can provide relevant information on climatic and hydroclimatic variations following major tropical volcanic eruptions, even when using the 5-year resolution wood samples of the Alpine Tree-Ring Isotope Record database.

The Unprecedented Character of California's 20th Century Enhanced Hydroclimatic Variability in a 600‐Year Context

AbstractRecently, year‐to‐year swings in California winter precipitation extremes have resulted in drought, wildfires, and floods causing billions of dollars in damage. These recent precipitation swings represent an increasing trend in variability of California's hydroclimate over the past decades. Here, we put this trend in a longer‐term context using tree‐ring‐based precipitation, streamflow, and snow water equivalent reconstructions. We show that the statewide rise in hydroclimate variability in the 20th century is driven by an increasing trend in the magnitude of wet extremes. A prior period of strong variability in the 16th century, in contrast, is related to an increasing trend in the magnitude of dry extremes. Our results are consistent with climate model simulations that suggest an increasingly volatile future for California's hydroclimate and highlight the importance of collaboration between scientists and water resource managers to incorporate this increased variability into their decision‐making and planning, acknowledging higher risks for compound events.

Changing flood dynamics in Norway since the last millennium and to the end of the 21st century

• All GCMs except MIROC-ESM simulate a higher mean temperature in Medieval Climate Anomaly (MCA) period than Little Ice Age (LIA) period, while simulated annual precipitation varies a lot in different GCMs and catchments. • No significant change of flood characteristics during the last millennium from ensemble-mean results. • In future, we will have an extraordinary shift in flood seasonality and generating processes, and flood frequency increase in most of the study catchments in Norway. • Climate projections represent the largest contribution to overall uncertainty in the projected changes in hydrological extremes for most of the catchments. With the recent warming trend over Europe and the Arctic, the Nordic regions have experienced more frequent and damaging extreme hydrological events which are anticipated to increase towards the end of the 21st century. Despite explicit trends, large variations have been observed across basins and regions when it comes to precipitation and floods hinting at a strong natural hydroclimatic variability that further complicates any assessment of potential future changes. In this study, we aim to better understand how climate variability links with the current extremes and future projections of floods in Norway in the context of the last millennium and the future. Specifically, we simulate over 1000 years (850–2099) daily discharge and floods at 34 catchments over five regions of Norway from the last millennium (including a warm period and a cold period; 850–1849) to the end of the 21st century by an ensemble model-chain method including four global climate models (GCMs), two bias-correction methods and two hydrological models. The modelling results show (i) all GCMs except MIROC-ESM simulate a higher mean temperature in Medieval Climate Anomaly (MCA) period than Little Ice Age (LIA) period, while simulated annual precipitation varies a lot in different GCMs and catchments, (ii) no significant change of flood characteristics during the last millennium from ensemble-mean results, (iii) in future, we will have an extraordinary shift in flood seasonality and generating processes, and flood frequency increase in most of the study catchments in Norway, and (iv) climate projections represent the largest contribution to overall uncertainty in the projected changes in hydrological extremes for most of the catchments.

Environmental Calibration of Coral Luminescence as a Proxy for Terrigenous Dissolved Organic Carbon Concentration in Tropical Coastal Oceans

AbstractThe riverine flux of terrigenous dissolved organic matter (tDOM) to the ocean is a significant contributor to the global carbon cycle. In response to anthropogenic drivers the flux is expected to increase. This may impact the availability of sunlight in coastal ecosystems, and the seawater carbonate system and coastal CO2 fluxes. Despite its significance, there are few long‐term and high‐resolution time series of tDOM parameters. Corals incorporate fluorescent tDOM molecules from the chromophoric dissolved organic matter (CDOM) pool in their skeletons. The resulting coral skeletal luminescence variability has traditionally been used to reconstruct hydroclimate variation. Here, we use two replicate coral cores and concurrent in‐situ biogeochemical data from the Sunda Shelf Sea in Southeast Asia, where peatlands supply high tDOM inputs, to show that variability in coral luminescence green‐to‐blue ratios (coral G/B) can be used to quantitatively reconstruct terrigenous dissolved organic carbon (tDOC) concentration. Moreover, coral G/B can be used to reconstruct the CDOM absorption spectrum from 230 to 550 nm, and the specific ultraviolet absorbance at 254 nm (SUVA254) of the DOM pool. Comparison to a core from Borneo shows that there may be site‐specific offsets in the G/B–CDOM absorption relationship, but that the slope of the relationship is very similar, validating the robustness of the proxy. By demonstrating that corals can be used to estimate past changes in coastal tDOC and CDOM, we establish a method to study drivers of land–ocean tDOM fluxes and their ecological consequences in tropical coastal seas over decadal to centennial time scales.