Role of dams in reducing global flood exposure under climate change

Dam construction alters the traits of health-related microbes along the Yangtze River

Dams, constructed globally for energy production and water conservation, fragment rivers, and modify flow regimes, thereby altering the composition of biological communities and ecosystem functions. Despite the extensive use of dams, few studies have explored their potential health impacts, particularly concerning changes in health-related genes, such as antibiotic resistance genes (ARGs) and virulence factor genes (VFGs), and their hosts (i.e., ARB and potential pathogens). Understanding these health-related effects is crucial because they can impact human health through water quality and pathogen prevalence. In this study, we investigated the planktonic microbial community in the Three Gorges Reservoir (TGR) and adjacent upstream and downstream areas of the Yangtze River during both the dry and wet season. Our metagenomic analysis showed that dam construction significantly decreased the abundance of ARGs, but it had an insignificant effect on VFGs. The observed reduction in ARGs abundance could be mainly attributed to the decrease abundance of the major ARGs carrier - Limnohabitansin the TGR and downstream areas due to high grazing pressure and fitness cost. Conversely, the abundance of microbes carrying VFGs (potential pathogens) remained stable from upstream to the dam reservoir, which may explain the negligible impact on VFG abundance. Overall, our results provide a detailed understanding of the ecological health implications of dam construction in large river ecosystems.

Global insights on flood risk mitigation in arid regions using geomorphological and geophysical modeling from a local case study

This research provides a comprehensive examination of flood risk mitigation in Saudi Arabia, with a focus on Wadi Al-Laith. It highlights the critical importance of addressing flood risks in arid regions, given their profound impact on communities, infrastructure, and the economy. Analysis of morphometric parameters ((drainage density (Dd), stream frequency (Fs), drainage intensity (Di), and infiltration number (If)) reveals a complex hydrological landscape, indicating elevated flood risk. due to low drainage density, low stream frequency, high bifurcation ratio, and low infiltration number. Effective mitigation strategies are imperative to protect both communities and infrastructure in Wadi Al-Laith. Geophysical investigations, using specialized software, improve the quality of the dataset by addressing irregularities in field data. A multi-layer geoelectric model, derived from vertical electrical sounding (VES) and time domain electromagnetic (TDEM) surveys, provides precise information about the geoelectric strata parameters such as electrical resistivity, layer thicknesses, and depths in the study area. This identifies a well-saturated sedimentary layer and a cracked rocky layer containing water content. The second region, proposed for a new dam, scores significantly higher at 56% in suitability compared to the first region's 44%. The study advocates for the construction of a supporting dam in the second region with a height between 230 and 280 m and 800 m in length. This new dam can play a crucial role in mitigating flash flood risks, considering various design parameters. This research contributes to flood risk management in Saudi Arabia by offering innovative dam site selection approaches. It provides insights for policymakers, researchers, and practitioners involved in flood risk reduction, water resource management, and sustainable development in arid regions globally.

Rethinking ecological niches and geographic distributions in face of pervasive human influence in the Anthropocene

Species are distributed in predictable ways in geographic spaces. The three principal factors that determine geographic distributions of species are biotic interactions (B), abiotic conditions (A), and dispersal ability or mobility (M). A species is expected to be present in areas that are accessible to it and that contain suitable sets of abiotic and biotic conditions for it to persist. A species' probability of presence can be quantified as a combination of responses to B, A, and M via ecological niche modeling (ENM; also frequently referred to as species distribution modeling or SDM). This analytical approach has been used broadly in ecology and biogeography, as well as in conservation planning and decision-making, but commonly in the context of 'natural' settings. However, it is increasingly recognized that human impacts, including changes in climate, land cover, and ecosystem function, greatly influence species' geographic ranges. In this light, historical distinctions between natural and anthropogenic factors have become blurred, and a coupled human-natural landscape is recognized as the new norm. Therefore, B, A, and M (BAM) factors need to be reconsidered to understand and quantify species' distributions in a world with a pervasive signature of human impacts. Here, we present a framework, termed human-influenced BAM (Hi-BAM, for distributional ecology that (i) conceptualizes human impacts in the form of six drivers, and (ii) synthesizes previous studies to show how each driver modifies the natural BAM and species' distributions. Given the importance and prevalence of human impacts on species distributions globally, we also discuss implications of this framework for ENM/SDM methods, and explore strategies by which to incorporate increasing human impacts in the methodology. Human impacts are redefining biogeographic patterns; as such, future studies should incorporate signals of human impacts integrally in modeling and forecasting species' distributions.

Climate control on the channel morphodynamics of the Sittaung River, Myanmar

The spatio-temporal development of a meandering river is controlled by its channel morphodynamics. In regions of rapid channel evolution, understanding the driving factors of meander migration is crucial in forecasting the rate and extent of morphological change. Sediment supply and fluvial discharge are the primary influences on migration rate, however climate oscillations are also integral in indirectly regulating migration rate through their control of regional precipitation, as well as the monsoon season of sub-tropical Asia. Despite this, an in-depth investigation into the impact of climate oscillations on meander bend migration remains undocumented. This study presents a satellite-based analysis of multi-decadal climatic forcing on the migration rate of the Sittaung River in Myanmar, through interpretation of the El Niño Southern Oscillation (ENSO). The mode of ENSO exerts significant climatic control on the migration rate of the meandering channels of the Sittaung River, with low-to-average migration rates recorded during dry El Niño events and peak migration rates observed during wet La Niña events. However, this climatic signal may have been obscured by certain local environmental conditions. In cases where meanders faced geological basement, the basement rock inhibited their migration through extension, forcing more rapid migration by way of seaward translation. Consequently, these translating meanders developed to be more elongate, with lower curvatures. Meanders downstream of the approximate tidal limit were less downstream skewed, indicative of tidal modulation, potentially obscuring the impact of fluvially driven climate forcing. Additionally, downstream of a major confluence, the input of sediment and fluvial discharge may have been regulated by upstream anthropogenic activities such as mining and dam construction, leading to greater variability in migration rate downstream of this confluence and further obfuscation of the climate signal.

Impacts of the Three Gorges Dam on riparian vegetation in the Yangtze River Basin under climate change

As the largest hydroelectric project in the world, the Three Gorges Dam (TGD) is expected to have significant environmental and ecological impacts on riparian vegetation in the Yangtze River Basin (YRB). However, existing studies have mainly focused on small segments of the YRB. In addition, few studies have quantified the responses of riparian vegetation to both climatic factors and dam construction. In this study, we investigated riparian vegetation dynamics over the entire YRB before, during, and after the construction of TGD from 1982 to 2015 using the normalized difference vegetation index (NDVI). Furthermore, the effects of climatic factors and dam construction on riparian vegetation were quantitatively analyzed using path analysis. The results demonstrate that the YRB has experienced a generally greening trend after TGD construction. The impacts of climate change on riparian vegetation have exhibited notable spatial heterogeneity and temperature is the main climatic factor that affects riparian vegetation growth. Moreover, TGD becomes the major contributor to riparian vegetation dynamics in the YRB after TGD construction. TGD has not only directly enhanced riparian vegetation but also indirectly affected riparian vegetation by regulating the microclimate. This study highlights the significance of anthropogenic interference when evaluating the relationships between riparian vegetation and climatic factors, providing useful insights for the effective management and conservation of large-scale riparian ecosystems.

Future sea level rise exacerbates compound floods induced by rainstorm and storm tide during super typhoon events: A case study from Zhuhai, China

Compound floods are becoming a growing threat in coastal cities against a background of global sea level rise (SLR), and may cause increasing impacts on societal safety and economy. How to quantify the impact of SLR and compound effects among various flood causes on compound flood have become important challenges. We propose a modeling framework which integrates atmospheric, storm tide and urban flood (IASTUF) models to characterize the various physical processes related to compound flood. Future SLR projections under various shared socioeconomic and respective concentration pathway emission scenarios are considered. Hengqin Island (Zhuhai City, China) frequently experiences typhoon conditions combined with rainstorm and storm surge events. Its population has increased more than sixfold during the past decade, stimulating urgent demands for assessments of the potential risks associated with future compound floods in the context of potential SLR. A compound flood event in northern Hengqin Island, caused by the super typhoon Mangkhut in 2018, is selected as a case study to verify the proposed modeling framework. Results show that the IASTUF modeling framework can capture well the combined processes of typhoon, rainstorm, storm tide and inland flooding and demonstrates good performance in quantifying compound flood magnitudes. Compared to the current scenario, the node flooding volume (from the drainage system) and the maximum inundation area (with inundation depths >1 m) in 2050 are projected to increase by 20-26 % and 41-85 %, respectively, and these increases rise to 46-84 % and 23-71 times by 2100. The inundation volumes and water depths due to compound events are larger than the sum of those caused by the corresponding single-cause events, indicating that concurrent rainstorm and storm surge induce positive compound effects on flood magnitude. These findings can provide guidance for the management and mitigation of future compound flood hazards driven by super typhoon events.

Population structure and demographic history for year cohort dynamics of landlocked ayu Plecoglossus altivelis altivelis in dam reservoir of Japan

Ayu Plecoglossus altivelis altivelis is a valuable osmeroid species for inland fishery in Japan. It is classified into two ecological forms of amphidromous migrating between rivers and sea and landlocked migrating between rivers and lakes or dam reservoirs. The number of dams and their reservoirs has remarkably increased in the twenty-first century under climate change, because of their respective roles in hydropower generation with negligible carbon emissions and in flood control. Dam reservoirs therefore become increasingly important as inland nursery grounds of ayu. In this study, we investigated the reproduction status of landlocked ayu migrating in the Haidzuka Dam reservoir and the Tabusa River in western Japan by molecular phylogenetic analysis based on population structure and demographic history for year cohort dynamics. A total of 849 individuals were collected monthly from October 2018 to September 2021 according to an annual life cycle of ayu. Nucleotide sequences of the partial mitochondrial DNA control region yielded 31 haplotypes, consisting of 4 shared haplotypes among the 2019, 2020 and 2021 cohorts and 27 unique haplotypes. The overall haplotype diversity and nucleotide diversity were calculated to be relatively low at 0.3503 ± 0.0206 and 0.0077 ± 0.0045, respectively, suggesting a founder event by dominant haplotypes. Star-shaped radiational haplotypes from dominant shared haplotypes on the median-joining network likely support a founder event. Although pairwise ФST values were determined to be very low among the year cohorts, only the 2019 cohort was found to have a significant difference from the 2020 and 2021 cohorts, for both of which Tajima's D values were also statistically significant. For the overall population, multimodal mismatch distribution and negative Tajima's D and Fu's Fs values in the neutrality test suggested population expansion or population subdivision. The native riverine population in the Tabusa River suffered habitat fragmentation and population bottleneck from dam construction, and therefore severe founder effect remained behind the artificially landlocked population with a low level of genetic diversity in the Haidzuka Dam reservoir.

Impacts of large-scale climatic circulation on floods through precipitation and temperature in the Lancang-Mekong River Basin

The importance of large-scale climatic circulation impacts on precipitation and floods in the Lancang-Mekong River Basin (LMRB) has been widely acknowledged. However, the mechanisms related to the impacts of circulation on floods are not yet fully understood. To address this issue, circulations were characterized by using the climate indices, and floods were represented by the flood volume and simulated using an improved hydrological-hydrodynamic model. The linear regression model was used to assess the impacts of circulation on precipitation and temperature, and also to quantify the impacts of precipitation, temperature, and circulation on floods. The results show that circulation affects precipitation with large spatial variability, while affects temperature with small spatial variability. On average, a unit change in different climate indices can cause a 2.5 %-6.1 % change in precipitation and a 0.3 %-1.2 % (0.09 °C-0.16 °C) change in temperature. Further, precipitation has a positive impact on floods, while temperature mainly has a negative impact. On average, a unit increase in precipitation and temperature can cause a 22.6 % increase and a 9.3 % decrease in floods, respectively. Consequently, circulation affects floods mainly through its impact on precipitation, while its impact on temperature also plays an important role. On average, a unit change in different climate indices can cause a 3.1 %-8.7 % change in floods. In addition, a multi-linear regression model was used to discuss the explained variance and relative contribution of climate. The results show that circulation can explain 12 %-23 % of the precipitation, temperature, and flood variances, while temperature and precipitation can explain 69 % of the flood variance. Among all circulations, the monsoon systems, North Atlantic Oscillation, and El Niño-Southern Oscillation dominate precipitation, temperature, and floods in the LMRB with the largest contributions and the most affected regions.

Higher emissions scenarios lead to more extreme flooding in the United States

Understanding projected changes in flooding across the contiguous United States (CONUS) helps increase our capability to adapt to and mitigate against this hazard. Here, we assess future changes in flooding across CONUS using outputs from 28 global climate models and four scenarios of the Coupled Model Intercomparison Project Phase 6. We find that CONUS is projected to experience an overall increase in flooding, especially under higher emission scenarios; there are subregional differences, with the Northeast and Southeast (Great Plains of the North and Southwest) showing higher tendency towards increasing (decreasing) flooding due to changes in flood processes at the seasonal scale. Moreover, even though trends may not be detected in the historical period, these projected future trends highlight the current needs for incorporating climate change in the future infrastructure designs and management of the water resources.

Anthropogenic climate change exacerbates the risk of successive flood-heat extremes: Multi-model global projections based on the Inter-Sectoral Impact Model Intercomparison Project

The successive flood-heat extreme (SFHE) event, which threatens the securities of human health, economy, and building environment, has attracted extensive research attention recently. However, the potential changes in SFHE characteristics and the global population exposure to SFHE under anthropogenic warming remain unclear. Here, we present a global-scale evaluation of the projected changes and uncertainties in SFHE characteristics (frequency, intensity, duration, land exposure) and population exposure under the Representative Concentration Pathway (RCP) 2.6 and 6.0 scenarios, based on the multi-model ensembles (five global water models forced by four global climate models) within the Inter-Sectoral Impact Model Intercomparison Project 2b framework. The results reveal that, relative to the 1970-1999 baseline period, the SFHE frequency is projected to increase nearly globally by the end of this century, especially in the Qinghai-Tibet Plateau (>20 events/30-year) and the tropical regions (e.g., northern South America, central Africa, and southeastern Asia, >15 events/30-year). The projected higher SFHE frequency is generally accompanied by a larger model uncertainty. By the end of this century, the SFHE land exposure is expected to increase by 12 % (20 %) under RCP2.6 (RCP6.0), and the intervals between flood and heatwave in SFHE tend to decrease by up to 3 days under both RCPs, implying the more intermittent SFHE occurrence under future warming. The SFHE events will lead to the higher population exposure in the Indian Peninsula and central Africa (<10 million person-days) and eastern Asia (<5 million person-days) due to the higher population density and the longer SFHE duration. Partial correlation analysis indicates that the contribution of flood to the SFHE frequency is greater than that of heatwave for most global regions, but the SFHE frequency is dominated by the heatwave in northern North America and northern Asia.

The impact of short-duration precipitation events over the historic Cauvery basin: a study on altered water resource patterns and associated threats

The Cauvery Delta, the 'Rice Bowl' of India follows a time-tested cultivation pattern over several irrigation zones. However, in this era of the Anthropocene, it is now well-established that short-duration, intense precipitation episodes will batter the flood plains year after year. The purpose of this first study is thus to quantify the impacts that such episodes may have on the floodplains of the Cauvery Delta and the concomitant threats to the historic Kallanai Dam. Precipitation events during the North-East monsoon period are driven not just by warm rain microphysics but also by large frozen hydrometeors falling from deep clouds causing undesirable flooding over the region to the extent of 66%. Additionally, from an assessment of the velocity heads and the floodwater depths, this study projects a heightened vulnerability. The total extent of submergence along riverbanks and other flow paths was estimated to be 145.98 [Formula: see text] out of which 65.14% of the submerged area is agricultural land. The most important conceptual advance established in this paper is that sub-zones in major watersheds that are currently safe will get inundated in the RCP8.5 warming scenario in 2050.

Hydropower: A low-hanging sour-sweet energy option for India

India is the world's second largest populous nation, fifth largest economy with seventh largest geographical area but experiences high energy poverty. With the lowest per capita energy consumption among world's top ten economies, India ranks at 137 out of 218 nations. Hydropower has the potential to alleviate India's energy asymmetry as well as realize its sustainable growth aspiration of a low-carbon regime. However, hydropower in India has been plagued by debates on human displacement, loss of biodiversity, increased risk of natural disasters, and socio-economic conflicts making it an unpopular energy alternative. Here, we review and address various concerns related to India's hydropower sector, examine scientific evidence, analyze energy policy imperatives, geopolitical considerations, and future directions for a sustainable hydropower policy in India in the context of ongoing climate change. Evidence indicates that besides electricity generation, hydropower infrastructure helps: (i) avert floods, (ii) mitigate the impacts of global warming, and (iii) ensure redistribution of water to arid regions and improve water security. As a part of sustainable hydropower policy, we propose that most of the ecological and social problems associated with hydropower development can be avoided to a great extent through careful planning, proper project design, responsible ownership, and public participation. As short-term measures, we propose: (i) entrepreneurs and planners follow credible and transparent pre-project investigations, (ii) mandatory implementation of environmental management plans, and (iii) better accountability and transparency of statutory bodies as well as hydropower developers. For long-term measures, we suggest: (i) create a 'National Institute of Energy & Environmental Sustainability' to oversee post-project hydropower developmental activities, (ii) streamline various bureaucratic and institutional procedures, and (ii) establish a trans-boundary water management system for seamless and coordinated implementation of hydropower development programs across upstream-downstream nations.

Overcoming the coupled climate and biodiversity crises and their societal impacts

Earth's biodiversity and human societies face pollution, overconsumption of natural resources, urbanization, demographic shifts, social and economic inequalities, and habitat loss, many of which are exacerbated by climate change. Here, we review links among climate, biodiversity, and society and develop a roadmap toward sustainability. These include limiting warming to 1.5°C and effectively conserving and restoring functional ecosystems on 30 to 50% of land, freshwater, and ocean "scapes." We envision a mosaic of interconnected protected and shared spaces, including intensively used spaces, to strengthen self-sustaining biodiversity, the capacity of people and nature to adapt to and mitigate climate change, and nature's contributions to people. Fostering interlinked human, ecosystem, and planetary health for a livable future urgently requires bold implementation of transformative policy interventions through interconnected institutions, governance, and social systems from local to global levels.

Flow regime changes in the Lancang River, revealed by integrated modeling with multiple Earth observation datasets

The flow regime change of rivers, especially transboundary rivers, affected by reservoir regulations is evident worldwide and has received much attention. Investigating dam-induced flow regime alterations is essential for understanding potential adverse downstream effects and facilitating dialogue around coordinated water use in transboundary basins, such as the Lancang River Basin (LRB). This study explored the value of combining several types of satellite Earth observation (EO) datasets that monitor different water balance components to constrain the parameter space of lumped conceptual hydrological models. Thus, we aimed to reconstruct the natural flow regimes upstream and downstream of the cascade reservoirs. Specifically, reservoir water storage changes were first estimated using satellite imagery and altimetry datasets. Then, storage changes were combined with hydrological model simulations of reservoir inflow to estimate the regulated flow regime downstream. Our results showed that integrated hydrological modeling combined with EO datasets exhibited better overall performance. Continuous warming and drying of the LRB resulted in a decrease in discharge of approximately 47 %. By comparing the simulated natural and regulated flow regimes, we revealed the pivotal role of the Xiaowan and Nuozhadu reservoirs in regulating natural flows. The wet season shortens (approximately 45 days), the flood peak flattens, and the low flow in the dry season has primarily increases. The two reservoirs attenuated 50 % of the flood peaks in the wet seasons and mitigated droughts by releasing up to 100 % of the natural flows in the dry seasons at the China-Laos border. Overall, these results enhance the understanding of upper reservoir operation, and the approaches can be applied to studies of dammed basins under climate change scenarios when knowledge of the upstream area is limited.

Response of dissolved organic matter chemistry to flood control of a large river reservoir during an extreme storm event

With the frequent occurrence of extreme floods under global climate change-induced storm events, reservoir operation has been highlighted for river flood control, complicating the transport and transformation of riverine dissolved organic matter (DOM), one of the largest reactive carbon pools on earth. In particular, the response of riverine DOM chemistry to reservoir flood control during extreme storm events is still unclear. To fill this knowledge gap, the mechanism of DOM variation in Yangtze River with the world's largest Three Gorges Reservoir (TGR) operation during an extreme storm event was explored. Optical and molecular properties of DOM varied significantly from upstream to downstream in non-TGR area, while no significant variation in DOM chemistry was observed in TGR area. The results uncovered a short time transformation of DOM from non-TGR area to TGR area, demonstrating that although storm event induced chemodiversity bloom of riverine DOM, flood control of TGR "re-constrained" DOM to more similar chemistry mainly under the influence of turbidity involved DOM transformation (e.g., adsorption/desorption and flocculation). Furthermore, combined with the hydrological information, we found that although TGR temporarily blocked dissolved organic carbon (DOC) flow during the flood event, the abundance of biologically recalcitrant DOC increased in TGR, which would contribute to its further transportation to downstream watershed. This study emphasizes the impact of TGR on extreme storm event-induced DOM dynamics, which also hints a better understanding of the crucial role of anthropogenic activity in affecting carbon cycling under extreme climate change.

Adaptation measures under the impacts of climate and land-use/land-cover changes using HSPF model simulation: Application to Gongola river basin, Nigeria

Recently, there is an upsurge in flood emergencies in Nigeria, in which their frequencies and impacts are expected to exacerbate in the future due to land-use/land cover (LULC) and climate change stressors. The separate and combined forces of these stressors on the Gongola river basin is feebly understood and the probable future impacts are not clear. Accordingly, this study uses a process-based watershed modelling approach - the Hydrological Simulation Program FORTRAN (HSPF) (i) to understand the basin's current and future hydrological fluxes and (ii) to quantify the effectiveness of five management options as adaptation measures for the impacts of the stressors. The ensemble means of the three models derived from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are employed for generating future climate scenarios, considering three distinct radiative forcing peculiar to the study area. Also, the historical and future LULC (developed from the hybrid of Cellular Automata and Markov Chain model) are used to produce the LULC scenarios for the basin. The effective calibration, uncertainty and sensitivity analyses are used for optimising the parameters of the model and the validated result implies a plausible model with efficiency of up to 75 %. Consequently, the results of individual impacts of the stressors yield amplification of the peak flows, with more profound impacts from climate stressor than the LULC. Therefore, the climate impact may trigger a marked peak discharge that is 48 % higher as compared to the historical peak flows which are equivalent to 10,000-year flood event. Whilst the combine impacts may further amplify this value by 27 % depending on the scenario. The proposed management interventions such as planned reforestation and reservoir at Dindima should attenuate the disastrous peak discharges by almost 36 %. Furthermore, the land management option should promote the carbon-sequestering project of the Paris agreement ratified by Nigeria. While the reservoir would serve secondary functions of energy production; employment opportunities, aside other social aspects. These measures are therefore expected to mitigate feasibly the negative impacts anticipated from the stressors and the approach can be employed in other river basins in Africa confronted with similar challenges.

Evaluation of potential changes in landslide susceptibility and landslide occurrence frequency in China under climate change

Climate change can alter the frequency and intensity of extreme rainfall across the globe, leading to changes in hazards posed by rainfall-induced landslides. In recent decades, China suffered great human and economic losses due to rainfall-induced landslides. However, how the landslide hazard situation will evolve in the future is still unclear, also because of sparse comprehensive evaluations of potential changes in landslide susceptibility and landslide occurrence frequency under climate change. This study builds upon observed and modelled rainfall data from 24 bias-corrected Coupled Model Intercomparison Project Phase 6 (CMIP6) Global Climate Models (GCMs), a statistical landslide susceptibility model, and empirical rainfall thresholds for landslide initiation, to evaluate changes in landslide susceptibility and landslide occurrence frequency at national-scale. Based on four Shared Socioeconomic Pathways (SSP) scenarios, changes in the rainfall regime are projected and used to evaluate subsequent alterations in landslide susceptibility and in the frequency of rainfall events exceeding empirical rainfall thresholds. In general, the results indicate that the extend of landslide susceptible terrain and the frequency of landslide-triggering rainfall will increase under climate change. Nevertheless, a closer inspection provides a spatially heterogeneous picture on how these landslide occurrence indicators may evolve across China. Until the late 21st century (2080-2099) and depending on the SSP scenarios, the mean annual precipitation is projected to increase by 13.4 % to 28.6 %, inducing an 1.3 % to 2.7 % increase in the modelled areal extent of moderately to very highly susceptible terrain. Different SSP scenarios were associated with an increase in the frequency of landslide-triggering rainfall events by 10.3 % to 19.8 % with respect to historical baseline. Spatially, the southeastern Tibetan Plateau and the Tianshan Mountains in Northwestern Basins are projected to experience the largest increase in landslide susceptibility and frequency of landslide-triggering rainfall, especially under the high emission scenarios. Adaptation and mitigation methods should be prioritized for these future landslide hotspots. This work provides a better understanding of potential impacts of climate change on landslide hazard across China and represents a first step towards national-scale quantitative landslide exposure and risk assessment under climate change.

Shifting in the global flood timing

Climate change will have an impact on not only flood magnitude but also on flood timing. This paper studies the shifting in flood timing at 6167 gauging stations from 1970 to 2010, globally. The shift in flood timing and its relationship with three influential factors (maximum 7-day precipitation, soil moisture excess, and snowmelt) are investigated. There is a clear global pattern in the mean flooding date: winter (Dec-Feb) across the western Coastal America, western Europe and the Mediterranean region, summer (Jun-Aug) in the north America, the Alps, Indian Peninsula, central Asia, Japan, and austral summer (Dec-Feb) in south Africa and north Australia area. The shift in flood timing has a trend from - 22 days per decade (earlier) to 28 days per decade (delayed). Earlier floods were found extensively in the north America, Europe and northeast Australia while delayed floods were prevailing in the Amazon, Cerrado, south Africa, India and Japan. Earlier flood timing in the north America and Europe was caused by earlier snowmelt while delayed extreme soil moisture excess and precipitation have jointly led to delayed floods around the monsoon zone, including south Africa, India and Japan. This study provides an insight on the shifting mechanism of flood timing, and supports decisions on the global flood mitigation and the impact from future climate change.

Water availability drives instream conditions and life-history of an imperiled desert fish: A case study to inform water management

In arid ecosystems, available water is a critical, yet limited resource for human consumption, agricultural use, and ecosystem processes-highlighting the importance of developing management strategies to meet the needs of multiple users. Here, we evaluated how water availability influences stream thermal regimes and life-history expressions of Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) in the arid Truckee River basin in the western United States. We integrated air temperature and stream discharge data to quantify how water availability drives stream temperature during annual spawning and rearing of Lahontan cutthroat trout. We then determined how in situ stream discharge and temperature affected adult spawning migrations, juvenile growth opportunities, and duration of suitable thermal conditions. Air temperatures had significant, large effects (+) on stream temperature across months; the effects of discharge varied across months, with significant effects (-) during May through August, suggesting increased discharge can help mitigate temperatures during seasonally warm months. Two models explained adult Lahontan cutthroat trout migration, and both models indicated that adult Lahontan cutthroat trout avoid migration when temperatures are warmer (~ > 12 °C) and discharge is higher (~ > 50 m³*s^-1). Juvenile size was best explained by a quadratic relationship with cumulative degree days (CDD; days>4 °C) as size increased with increasing CDDs but decreased at higher CDDs. We also found an interaction between CDDs and discharge explaining juvenile size: when CDDs were low, higher discharge was associated with larger size, but when CDDs were high, higher discharge was associated with smaller size. Stream temperatures also determined the duration of juvenile rearing, as all juvenile emigration ceased at temperatures >24.4 °C. Together, our results illustrated how stream discharge and temperature shape the life-history of Lahontan cutthroat trout at multiple stages and can inform management actions to offset warming temperatures and facilitate life-history diversity and population resilience.

A Comprehensive Approach for Floodplain Mapping through Identification of Hazard Using Publicly Available Data Sets over Canada

Quantifying flood inundation and hazards over large regions is paramount for gaining critical information on flood risk over the vulnerable population and environment. Readily available global data and enhancement in computational simulations have made it easier to simulate flooding at a large scale. This study explores the usability of publicly available datasets in flood inundation and hazard mapping, and ensures the flood-related information reaches the end-users efficiently. Runoff from the North American Regional Reanalysis and other relevant inputs are fed to the CaMa-Flood model to generate flooding patterns for 1 in 100 and 1 in 200-year return period events over Canada. The simulated floodplain maps are overlaid on the property footprints of 34 cities (falling within the top 100 populated cities of Canada) to determine the degree of exposure during 1991, 2001 and 2011. Lastly, Flood Map Viewer—a web-based public tool, is developed to disseminate extensive flood-related information. The development of the tool is motivated by the commitment of the Canadian government to contribute $63 M over the next three years for the development of flood maps, especially in high-flood risk areas. The results from the study indicate that around 80 percent of inundated spots belong to high and very-high hazard classes in a 200-year event, which is roughly 4 percent more than observed during the 100-year event. We notice an increase in the properties exposed to flooding during the last three decades, with a signature rise in Toronto, Montreal and Edmonton. The flood-related information derived from the study can be used along with vulnerability and exposure components to quantify flood risk. This will help develop appropriate pathways for resilience building for long-term sustainable benefits.

Centennial Precipitation Characteristics Change in Haihe River Basin, China

Research on precipitation regularity in the past 120 years is an important link in analyzing the precipitation characteristics of watersheds. This paper systematically analyzes the characteristic changes of centennial precipitation data in the Haihe River basin with the help of CRU data, PCI, SPI, and the Pearson type III curve. The results show that the spatial and temporal distribution of precipitation in the Haihe River basin has a more obvious inconsistency. The temporal distribution shows the characteristics of relatively stable in the early period and increasing fluctuation in the later period, the concentration of precipitation gradually decreases, and the overall drought level decreases. The spatial distribution shows a general pattern of gradually decreasing from southwest to northeast, the overall trend of summer precipitation changes from stable to north–south extremes, and the distribution probability of extreme precipitation events in the basin decreases from southeast to northwest, while the drought-prone area transitions from the northeast to the west and southwest of the basin. Under the influence of both climate change and human activities, the seasonal distribution of precipitation tends to be average, the area affected by extreme precipitation rises, and the arid area shifts to the inland area.

Integrated Transcriptomic and Proteomic Analyses Uncover the Regulatory Mechanisms of Myricaria laxiflora Under Flooding Stress

Flooding is one of the major environmental stresses that severely influence plant survival and development. However, the regulatory mechanisms underlying flooding stress remain largely unknown in Myricaria laxiflora, an endangered plant mainly distributed in the flood zone of the Yangtze River, China. In this work, transcriptome and proteome were performed in parallel in roots of M. laxiflora during nine time-points under the flooding and post-flooding recovery treatments. Overall, highly dynamic and stage-specific expression profiles of genes/proteins were observed during flooding and post-flooding recovery treatment. Genes related to auxin, cell wall, calcium signaling, and MAP kinase signaling were greatly down-regulated exclusively at the transcriptomic level during the early stages of flooding. Glycolysis and major CHO metabolism genes, which were regulated at the transcriptomic and/or proteomic levels with low expression correlations, mainly functioned during the late stages of flooding. Genes involved in reactive oxygen species (ROS) scavenging, mitochondrial metabolism, and development were also regulated exclusively at the transcriptomic level, but their expression levels were highly up-regulated upon post-flooding recovery. Moreover, the comprehensive expression profiles of genes/proteins related to redox, hormones, and transcriptional factors were also investigated. Finally, the regulatory networks of M. laxiflora in response to flooding and post-flooding recovery were discussed. The findings deepen our understanding of the molecular mechanisms of flooding stress and shed light on the genes and pathways for the preservation of M. laxiflora and other endangered plants in the flood zone.

Non-Stationary Hydrological Regimes Due to Climate Change: The Impact of Future Precipitation in the Spillway Design of a Reservoir, Case Study: Sube y Baja Dam, in Ecuador

Changes in flood loads and reservoir levels, produced by climate change (CC), represent an increasing concern for dam safety managers and downstream populations, highlighting the need to define adaptation strategies based on the dam failure risk management framework. Currently, thousands of dams worldwide, varying in use, age, and maintenance, may represent a threat to downstream cities in the case of structural failure. Several studies relate the failure of dams to several issues in the spillway, which may be even more vulnerable in CC conditions. This study provides a review of dam safety threats due to CC and approaches for the design/redesign of the spillway to cope with CC. A general four-stage methodology is proposed: data gathering and hydro-climatic, hydrological, and hydraulic analyses. Afterward, this methodology is applied to the spillway design for the Sube y Baja dam in Ecuador. The Probable Maximum Precipitation (PMP) increases around 20% considering CC under the Representative Concentration Pathway 8.5. Such an increment derived a 25% increase in the spillway maximum flow. These results show that the non-stationary hydrological regimes related to CC require a revision of engineering design criteria for hydraulic structures in general, and call for a consensus on design variables under CC.

Modeling the Territorial Structure Dynamics of the Northern Part of the Volga-Akhtuba Floodplain

The subject of our study is the tendency to reduce the floodplain area of regulated rivers and its impact on the degradation of the socio-environmental systems in the floodplain. The aim of the work is to create a new approach to the analysis and forecasting of the multidimensional degradation processes of floodplain territories under the influence of natural and technogenic factors. This approach uses methods of hydrodynamic and geoinformation modeling, statistical analysis of observational data and results of high-performance computational experiments. The basis of our approach is the dynamics model of the complex structure of the floodplain. This structure combines the characteristics of the frequency ranges of flooding and the socio-environmental features of various sites (cadastral data of land use). Modeling of the hydrological regime is based on numerical shallow water models. The regression model of the technogenic dynamics of the riverbed allowed us to calculate corrections to the parameters of real floods that imitate the effect of this factor. This made it possible to use digital maps of the modern topography for hydrodynamic modeling and the construction of floods maps for past and future decades. The technological basis of our study is a set of algorithms and software, consisting of three modules. The data module includes, first of all, the cadastres of the territory of the Volga-Akhtuba floodplain (VAF, this floodplain is the interfluve of the Volga and Akhtuba rivers for the last 400 km before flowing into the Caspian Sea), satellite and natural observation data, spatial distributions of parameters of geoinformation and hydrodynamic models. The second module provides the construction of a multilayer digital model of the floodplain area, digital maps of floods and their aggregated characteristics. The third module calculates a complex territorial structure, criteria for the state of the environmental and socio-economic system (ESES) and a forecast of its changes. We have shown that the degradation of the ESES of the northern part of the VAF is caused by the negative dynamics of the hydrological structure of its territory, due to the technogenic influence the hydroelectric power station on the Volga riverbed. This dynamic manifests itself in a decrease in the stable flooded area and an increase in the unflooded and unstable flooded areas. An important result is the forecast of the complex territorial structure and criteria for the state of the interfluve until 2050.

Buffering the impacts of extreme climate variability in the highly engineered Tigris Euphrates river system

More extreme and prolonged floods and droughts, commonly attributed to global warming, are affecting the livelihood of major sectors of the world’s population in many basins worldwide. While these events could introduce devastating socioeconomic impacts, highly engineered systems are better prepared for modulating these extreme climatic variabilities. Herein, we provide methodologies to assess the effectiveness of reservoirs in managing extreme floods and droughts and modulating their impacts in data-scarce river basins. Our analysis of multiple satellite missions and global land surface models over the Tigris-Euphrates Watershed (TEW; 30 dams; storage capacity: 250 km³), showed a prolonged (2007–2018) and intense drought (Average Annual Precipitation [AAP]: < 400 km³) with no parallels in the past 100 years (AAP during 1920–2020: 538 km³) followed by 1-in-100-year extensive precipitation event (726 km³) and an impressive recovery (113 ± 11 km³) in 2019 amounting to 50% of losses endured during drought years. Dam reservoirs captured water equivalent to 40% of those losses in that year. Additional studies are required to investigate whether similar highly engineered watersheds with multi-year, high storage capacity can potentially modulate the impact of projected global warming-related increases in the frequency and intensity of extreme rainfall and drought events in the twenty-first century.

Streamflow Prediction in Highly Regulated, Transboundary Watersheds Using Multi-Basin Modeling and Remote Sensing Imagery

Despite the potential of remote sensing for monitoring reservoir operation, few studies have investigated the extent to which reservoir releases can be inferred across different spatial and temporal scales. Through evaluating 21 reservoirs in the highly regulated Greater Mekong region, remote sensing imagery was found to be useful in estimating daily storage volumes for within-year and over-year reservoirs (correlation coefficients [CC] ≥ 0.9, normalized root mean squared error [NRMSE] ≤ 31%), but not for run-of-river reservoirs (CC < 0.4, 40% ≤ NRMSE ≤ 270%). Given a large gap in the number of reservoirs between global and local databases, the proposed framework can improve representation of existing reservoirs in the global reservoir database and thus human impacts in hydrological models. Adopting an Integrated Reservoir Operation Scheme within a multi-basin model was found to overcome the limitations of remote sensing and improve streamflow prediction at ungauged cascade reservoir systems where previous modeling approaches were unsuccessful. As a result, daily regulated streamflow was predicted competently across all types of reservoirs (median values of CC = 0.65, NRMSE = 8%, and Kling-Gupta efficiency [KGE] = 0.55) and downstream hydrological stations (median values of CC = 0.94, NRMSE = 8%, and KGE = 0.81). The findings are valuable for helping to understand the impacts of reservoirs and dams on streamflow and for developing more useful adaptation measures to extreme events in data sparse river basins.

ResOpsUS, a dataset of historical reservoir operations in the contiguous United States

There are over 52,000 dams in the contiguous US ranging from 0.5 to 243 meters high that collectively hold 600,000 million cubic meters of water. These structures have dramatically affected the river dynamics of every major watershed in the country. While there are national datasets that document dam attributes, there is no national dataset of reservoir operations. Here we present a dataset of historical reservoir inflows, outflows and changes in storage for 679 major reservoirs across the US, called ResOpsUS. All of the data are provided at a daily temporal resolution. Temporal coverage varies by reservoir depending on construction date and digital data availability. Overall, the data spans from 1930 to 2020, although the best coverage is for the most recent years, particularly 1980 to 2020. The reservoirs included in our dataset cover more than half of the total storage of large reservoirs in the US (defined as reservoirs with storage greater 0.1 km³). We document the assembly process of this dataset as well as its contents. Historical operations are also compared to static reservoir attribute datasets for validation.

Measurement(s)	storage • inflow • outflow • evaporation • elevation
Technology Type(s)	digital curation
Factor Type(s)	temporal interval
Sample Characteristic - Environment	reservoir
Sample Characteristic - Location	contiguous United States of America

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.17161415

Climate change and hydrological regime in arid lands: Impacts of dams on the plant diversity, vegetation structure and soil in Saudi Arabia

As the direct effects of climate change on the hydrological regime, Saudi Arabia has constructed more than 522 dams of various capacities as part of economic and environmental development. The study aims to assess the impact of dams on plant diversity, vegetation structure and soil in Saudi Arabia. Thirty-five stands were selected from the dams of different sizes of Saudi Arabia. Vegetation samples were established before (upstream) and after (downstream) the dam, and at the undammed (unaffected by the dam) to compare species diversity in the dam sites and undammed sites and to document the potential effects of dams on vegetation structure. A total of 151 plant species belonging to 36 families have been recorded. The vegetation associations are essentially shrubby with widespread annuals. Six novel associations were identified with the application of TWINSPAN, DCA, and CCA programs. They were named after the characteristic species as follows: VG I: Acacia gerrardii-Caralluma retrospiciens; VGII: Acacia tortilis-Maerua oblongifolia; VGIII: Lycium shawii-Farsetia aegyptiaca; VG IV: Farsetia stylosa-Cornulaca monocantha; VG V: Suaeda aegyptiaca-Salsola imbricata-Prosopis farcta and VGVI: Xanthium strumarium-Ochradenus baccatus. These plant communities are evaluated and discussed according to their floristic structure, vegetation diversity and edaphic variables. The riparian or streamside zones upstream and downstream that are periodically flooded contain highly diverse plant communities that are structured by flooding, which creates disturbance and acts as a dispersal mechanism for plants than undammed sites.

Linking reservoir ecosystems research to the sustainable development goals

Reservoirs account for about 10% of the freshwater stored in lakes worldwide. These reservoirs are home to 'reservoir ecosystems', that is, the aquatic and non-aquatic interactive ecosystems associated with artificial lakes where water is stored, typically behind a dam, for human purposes. While reservoir ecosystems provide various ecosystem services for sustainable development, their significance in research and policy has not been well understood and not well defined in the 2030 United Nation's (UN) Agenda for Sustainable Development. To advance understanding of reservoir ecosystems and their impact on policy, here we provide an overview of research on reservoir ecosystems and link it to UN SDGs and their Targets. Based on 5280 articles published in the last three decades, we applied network visualization to construct a framework for research addressing reservoir ecosystems. The framework covers four major themes: (1) ecosystem structure and function, (2) environmental pollution and stress effects, (3) climate impacts and ecological feedbacks, and (4) ecosystem services and management. We have found that sustainable reservoir ecosystems synergistically support 121 Targets of UN SDGs (71% of all). Reservoir ecosystems have both negative and positive implications for 15 targets (9%) and negative trade-offs for only 3 targets (2%). Thirty SDG Targets (18%) are unrelated to sustainable reservoir ecosystems. The synergies and trade-offs exist in three fields, securing basic material needs (SDGs 2, 6, 7, 14 and 15), pursuing common human well-being (SDGs 1, 3, 4, 5, 8 and 10), and coordinating sustainable governance policies (SDGs 9, 11, 12, 13, 16 and 17). Exploring these linkages allows better integration of reservoir ecosystems into the UN SDGs framework and guides sustainable management of reservoir ecosystems for sustainable development.