The everyday of inundation: livelihoods and lifeways dimensions of flooding experience in Amazonian Peru

New York City Panel on Climate Change 2019 Report Chapter 5: Mapping Climate Risk

BackgroundAn increasing severity of extreme storms and more intense seasonal flooding are projected consequences of climate change in the United States. In addition to the immediate destruction caused by storm surges and catastrophic flooding, these events may also increase the risk of infectious disease transmission. We aimed to determine the association between extreme and seasonal floods and hospitalizations for Legionnaires’ disease in 25 US states during 2000–2011.MethodsWe used a nonparametric bootstrap approach to examine the association between Legionnaires’ disease hospitalizations and extreme floods, defined by multiple hydrometeorological variables. We also assessed the effect of extreme flooding associated with named cyclonic storms on hospitalizations in a generalized linear mixed model (GLMM) framework. To quantify the effect of seasonal floods, we used multi-model inference to identify the most highly weighted flood-indicator variables and evaluated their effects on hospitalizations in a GLMM.ResultsWe found a 32% increase in monthly hospitalizations at sites that experienced cyclonic storms, compared to sites in months without storms. Hospitalizations in months with extreme precipitation were in the 89th percentile of the bootstrapped distribution of monthly hospitalizations. Soil moisture and precipitation were the most highly weighted variables identified by multi-model inference and were included in the final model. A 1-standard deviation (SD) increase in average monthly soil moisture was associated with a 49% increase in hospitalizations; in the same model, a 1-SD increase in precipitation was associated with a 26% increase in hospitalizations.ConclusionsThis analysis is the first to examine the effects of flooding on hospitalizations for Legionnaires’ disease in the United States using a range of flood-indicator variables and flood definitions. We found evidence that extreme and seasonal flooding is associated with increased hospitalizations; further research is required to mechanistically establish whether floodwaters contaminated with Legionella bacteria drive transmission.

Ammonia oxidation is the rate-limiting first step of nitrification and a key process in the nitrogen cycle that results in the formation of nitrite (NO2–), which can be further oxidized to nitrate (NO3–). In the Amazonian floodplains, soils are subjected to extended seasons of flooding during the rainy season, in which they can become anoxic and produce a significant amount of methane (CH4). Various microorganisms in this anoxic environment can couple the reduction of different ions, such as NO2– and NO3–, with the oxidation of CH4 for energy production and effectively link the carbon and nitrogen cycle. Here, we addressed the composition of ammonium (NH4+) and NO3–—and NO2–—dependent CH4-oxidizing microbial communities in an Amazonian floodplain. In addition, we analyzed the influence of environmental and geochemical factors on these microbial communities. Soil samples were collected from different layers of forest and agroforest land-use systems during the flood and non-flood seasons in the floodplain of the Tocantins River, and next-generation sequencing of archaeal and bacterial 16S rRNA amplicons was performed, coupled with chemical characterization of the soils. We found that ammonia-oxidizing archaea (AOA) were more abundant than ammonia-oxidizing bacteria (AOB) during both flood and non-flood seasons. Nitrogen-dependent anaerobic methane oxidizers (N-DAMO) from both the archaeal and bacterial domains were also found in both seasons, with higher abundance in the flood season. The different seasons, land uses, and depths analyzed had a significant influence on the soil chemical factors and also affected the abundance and composition of AOA, AOB, and N-DAMO. During the flood season, there was a significant correlation between ammonia oxidizers and N-DAMO, indicating the possible role of these oxidizers in providing oxidized nitrogen species for methanotrophy under anaerobic conditions, which is essential for nitrogen removal in these soils.

An important aspect of economic considerations is the routing and safety of hydraulic storage facilities such as dams for extreme probable water flooding. The routing of dam reservoirs requires more attention for determining the magnitude of extreme probable flooding. Apparently, the type of structure, importance, and economic development of the surrounding area guide the routing criteria for choosing the extreme flood magnitude. The Maithan and Panchet Dams in India have faced several major floods with diversified magnitudes since 1978. The present study aims to estimate the storage and routing of extreme probable floodings for these two dams based on real-time flood data like inflow, outflow, and elevation for the extreme flood years of 1978, 2009, and 2014. Reservoir storages at different elevations are calculated from the initial storage volumes. For both reservoirs, discharge equations are derived and calculated at given elevations during extreme floods. The Modified Puls technique is used for routing extreme floods. At the end of each extreme flood in 1978, 2009, and 2014, the variation in outflow discharges at different elevations and flood hydrographs is predicted. Finally, estimated outflow discharges are compared with the actual outflow discharges for the given inflows during extreme floods. Using this approach, extreme floods that occurred in 1978 are predicted with less than 10% error. Outcomes from this study may help in the future planning and routing of flood-control detention facilities and in predicting the variation in outflow discharges at different elevations. Based on this work, alternative studies and regional drainage planning can also be carried out.

The annual flood cycle is integral to rural life and livelihoods in riparian Amazonia. Livelihoods are built around the flood cycle, which facilitates transportation and affects soil fertility and fish migrations. Flood extremes, however, can have devastating impacts for riverine populations, yet there is minimal understanding of what distinguishes a 'normal' flood from a 'bad' flood, or flooding as integral to riverine settlement from flooding as environmental hazard. We address this limitation by drawing upon hydrograph data and field data collected in a riverine village in the Peruvian Amazon. We define four extreme flood types based on height, duration, and timing of onset, and illustrate how they each create a unique combination of negative and positive implications. We discuss the integral role of fishing to floodplain livelihoods during the flood season, and the implications of flood extremes for health, safety, and food provision. The article proposes a more nuanced conceptualization of flooding in riverine Amazonia to better inform policies and practices aimed at supporting local populations during extreme floods.

An analysis of extreme flood events during the past 400 years at Taihu Lake, China

Floodplain soils within mountainous watersheds are dynamic reservoirs of carbon (C), and experience seasonal flooding due to snowmelt and drainage. Climate change is shifting snowpack levels, making these ecosystems vulnerable to more frequent extreme flood and drought years. Here we show how extreme flooding or drought events, and associated variations in redox conditions, impact the dominant controls on microbial C cycling within and export from floodplain soils. Employing in-field monitoring with advanced analytical and molecular tools in the subalpine East River watershed (Gothic, Colorado) we compared seasonal flooding impacts in extremely low and high river discharge years (2018 and 2019, respectively), foreshadowing climate change projections. Our results show that reduced conditions during flooded periods caused reductive dissolution of Fe oxide minerals, mobilizing previously mineral-bound organic C and enhancing export of dissolved organic carbon (DOC). At the same time, flooding decreased CO2 production and selectively preserved chemically reduced DOC, likely due to metabolic constraints on microbial respiration. Upon drainage and re-oxygenation of floodplain soils, however, CO2 production increased, but was limited by the concurrant entrapment of DOC by newly precipitated Fe oxides within the soils. Compared to the low discharge year, extreme flooding during high dicharge years underminded mineral protection and heightened mineral constraints, suppressing CO2 production and enhanced DOC export from floodplain soils. We conclude that seasonal flooding events shift the relative and interactive impacts of mineral and metabolic constraints on microbial C cycling in floodplains, altering the balance between CO2 and DOC export. Our results suggest that extreme hydrological events expected with climate change will shift the control on and pathways of C loss from floodplains.

Flood dynmics in the Vietnamese Mekong Delta : Current state and future projections

Abstract. Using a 17-site seasonal precipitation reconstruction from a unique historical archive, Yu-Xue-Fen-Cun, the decadal variations of extreme droughts and floods (i.e., the event with occurrence probability of less than 10 % from 1951 to 2000) in North China were investigated, by considering both the probabilities of droughts/floods occurrence in each site and spatial coverage (i.e., percentage of sites). Then, the possible linkages of extreme droughts and floods with ENSO (i.e., El Niño and La Niña) episodes and large volcanic eruptions were discussed. The results show that there were 29 extreme droughts and 28 extreme floods in North China from 1736 to 2000. For most of these extreme drought (flood) events, precipitation decreased (increased) evidently at most of the sites for the four seasons, especially for summer and autumn. But in drought years of 1902 and 1981, precipitation only decreased in summer slightly, while it decreased evidently in the other three seasons. Similarly, the precipitation anomalies for different seasons at different sites also existed in several extreme flood years, such as 1794, 1823, 1867, 1872 and 1961. Extreme droughts occurred more frequently (2 or more events) during the 1770s–1780s, 1870s, 1900s–1930s and 1980s–1990s, among which the most frequent (3 events) occurred in the 1900s and the 1920s. More frequent extreme floods occurred in the 1770s, 1790s, 1820s, 1880s, 1910s and 1950s–1960s, among which the most frequent (4 events) occurred in the 1790s and 1880s. For the total of extreme droughts and floods, they were more frequent in the 1770s, 1790s, 1870s–1880s, 1900s–1930s and 1960s, and the highest frequency (5 events) occurred in the 1790s. A higher probability of extreme drought was found when El Niño occurred in the current year or the previous year. However, no significant connections were found between the occurrences of extreme floods and ENSO episodes, or the occurrences of extreme droughts/floods and large volcanic eruptions.

Flood hazards for a 9-mile reach of Fortymile Wash and its principal southwestern tributaries - Busted Butte, Drill Hole, and Yucca Washes - were evaluated to aid in determining possible sites for the storage of high-level radioactive wastes on the Nevada Test Site. Data from 12 peak-flow gaging stations adjacent to the Test Site were used to develop regression relations that would permit an estimation of the magnitude of the 100- and 500-year flood peaks (Q{sub 100} and Q{sub 500}), in cubic feet per second. The resulting equations are: Q{sub 100} = 482A{sup 0} {sup 565} and Q{sub 500} = 2200A{sup 0} {sup 571}, where A is the tributary drainage area, in square miles. The estimate of the regional maximum flood was based on data from extreme floods elsewhere in Nevada and in surrounding states. Among seven cross sections on Fortymile Wash, the estimated maximum depths of the 100-year, 500-year, and regional maximum floods are 8, 11, and 29 feet, respectively. At these depths, flood water would remain within the deeply incised channel of the wash. Mean flow velocities would be as great as 9, 14, and 28 feet per second for the three respective flood magnitudes. The study showsmore » that Busted Butte and Drill Hole Washes (9 and 11 cross sections, respectively) would have water depths of up to at least 4 feet and mean flow velocities of up to at least 8 feet per second during a 100-year flood. A 500-year flood would exceed stream-channel capacities at several places, with depths to 10 feet and mean flow velocities to 11 feet per second. The regional maximum flood would inundate sizeable areas in central parts of the two watersheds. At Yucca Wash (5 cross sections), the 100-year, 500-year, and regional maximum floods would remain within the stream channel. Maximum flood depths would be about 5, 9, and 23 feet and mean velocities about 9, 12, and 22 feet per second, respectively, for the three floods.« less

The new maximum recorded river flows in Scotland since 1988 have triggered widespread interest in whether floods are becoming more frequent and in the conditions that generate floods of different magnitudes and frequencies. There are questions about the longer‐term variability in flood‐generating characteristics, and whether there are past analogues for present hydroclimatic variability. The present paper builds on previous work reconstructing a detailed historic flood chronology for the Tay, the largest catchment in Scotland, and its tributaries over the past 800 years, extending the gauged discharge record (1952 onwards). It categorizes flood‐generating factors in the Tay catchment and analyses the hydro‐meteorological conditions that have generated extreme and moderate floods over a historical period. This work is placed in a broader literature context of historical ‘climaxes of storminess’, periods of higher storm frequency, flood patterns observed in Scotland and Europe during the Little Ice Age and longer‐term rainfall and temperature patterns. The paper concludes that the variability in flood‐generating characteristics is highly dependent on the timescale of observation. Inevitably the relative dominance of winter and early spring flooding can vary from year to year and within specific time‐periods, but so can the level of augmentation of the flood series with summer and autumn floods to produce notable ‘flood years’ and flood clusters. The Tay provides a good ‘all‐Scotland surrogate’ for historical flood patterns, reflecting its gathering areas in eastern and western Scotland. The value of a historical approach to the assessment of flood seasonality and generating characteristics is clearly demonstrated.

Abstract. Lowland karst aquifers can generate unique wetland ecosystems which are caused by groundwater fluctuations that result in extensive groundwater–surface water interactions (i.e. flooding). However, the complex hydrogeological attributes of these systems, linked to extremely fast aquifer recharge processes and flow through well-connected conduit networks, often present difficulty in predicting how they will respond to changing climatological conditions. This study investigates the predicted impacts of climate change on a lowland karst catchment by using a semi-distributed pipe network model of the karst aquifer populated with output from the high spatial resolution (4 km) Consortium for Small-scale Modelling Climate Lokalmodell (COSMO-CLM) regional climate model simulations for Ireland. An ensemble of projections for the future Irish climate were generated by downscaling from five different global climate models (GCMs), each based on four Representative Concentration Pathways (RCPs; RCP2.6, RCP4.5, RCP6.0 and RCP8.5) to account for the uncertainty in the estimation of future global emissions of greenhouse gases. The one-dimensional hydraulic/hydrologic karst model incorporates urban drainage software to simulate open channel and pressurised flow within the conduits, with flooding on the land surface represented by storage nodes with the same stage volume properties of the physical turlough basins. The lowland karst limestone catchment is located on the west coast of Ireland and is characterised by a well-developed conduit-dominated karst aquifer which discharges to the sea via intertidal and submarine springs. Annual above ground flooding associated with this complex karst system has led to the development of unique wetland ecosystems in the form of ephemeral lakes known as turloughs; however, extreme flooding of these features causes widespread damage and disruption in the catchment. This analysis has shown that mean, 95th and 99th percentile flood levels are expected to increase by significant proportions for all future emission scenarios. The frequency of events currently considered to be extreme is predicted to increase, indicating that more significant groundwater flooding events seem likely to become far more common. The depth and duration of flooding is of extreme importance, both from an ecological perspective in terms of wetland species distribution and for extreme flooding in terms of the disruption to homes, transport links and agricultural land inundated by flood waters. The seasonality of annual flooding is also predicted to shift later in the flooding season, which could have consequences in terms of ecology and land use in the catchment. The investigation of increasing mean sea levels, however, showed that anticipated rises would have very little impact on groundwater flooding due to the marginal impact on ebb tide outflow volumes. Overall, this study highlights the relative vulnerability of lowland karst systems to future changing climate conditions, mainly due to the extremely fast recharge which can occur in such systems. The study presents a novel and highly effective methodology for studying the impact of climate change in lowland karst systems by coupling karst hydrogeological models with the output from high-resolution climate simulations.

Based on the data of precipitation from 1951 to 2014 in Xi’an,Shanxi Province,China(hereinafter referred to as Xi’an),after analyzing the characteristics of changes in precipitation over the last 64 years,the multiple scale analysis of annual precipitation and flood season precipitation are analyzed by wavelet analysis in Xi'an.The conclusions are as follows:(1)Flood season precipitation accounts for 79.32% of annual precipitation, and the correlation coefficient is 0.94,so,the contribution of precipitation in flood season to annual precipitation is very great.(2) Annual precipitation and flood season precipitation shows a decreasing trend, with a decreasing rate of -11.3mm/10a and -3.17mm /10a, respectively,which shows 72% of the annual precipitation decreases in the non flood season.(3)Annual precipitation sequence and flood season precipitation sequence have the similar main cycle in Xi'an.Their first main periods are 29 years and 31 years, respectively, and the second, the third,the forth main cycles all are 13 years, 6 years and 3 years.(4)Over any time scale,the annual precipitation and the precipitation in flood season will be into a less period after 2014.Since the oscillation intensities of the first and the second main cycles of annual precipitation is basically same,the possibilities of the less period of annual precipitation continuing to 2020 or 2017 are the same.However,the oscillation intensity of the first main cycle of precipitation in flood season is much greater than that of the second main cycle,so the probability of the less period of precipitation in the flood season is more likely to continue to 2020 than 2017.

This paper provides a synoptic view of extreme monsoon floods on all the nine large rivers of South Asia and their association with the excess (above-normal) monsoon rainfall periods. Annual maximum flood series for 18 gauging stations spread over four countries (India, Pakistan, Bangladesh and Nepal) and long-term monsoon rainfall data were analyzed to ascertain whether the extreme floods were clustered in time and whether they coincided with multi-decade excess monsoon rainfall epochs at the basin level. Simple techniques, such as the Cramer’s t-test, regression and Mann–Kendall (MK) tests and Hurst method were used to evaluate the trends and patterns of the flood and rainfall series. MK test reveals absence of any long-term tendency in all the series. However, the Cramer’s t test and Hurst-Mandelbrot rescaled range statistic provide evidence that both rainfall and flood time series are persistent. Using the Cramer’s t-test the excess monsoon epochs for each basin were identified. The excess monsoon periods for different basins were found to be highly asynchronous with respect to duration as well as the beginning and end. Three main conclusions readily emerge from the analyses. Extreme floods (>90th percentile) in South Asia show a tendency to cluster in time. About three-fourth of the extreme floods have occurred during the excess monsoon periods between ~1840 and 2000 AD, implying a noteworthy link between the two. The frequency of large floods was higher during the post-1940 period in general and during three decades (1940s, 1950s and 1980s) in particular.

New England and Atlantic Canada are characterized by mixed flood regimes that reflect different storm types, antecedent land surface conditions, and flood seasonality. Mixed flood regimes are known to complicate flood risk analyses, yet the synoptic climatology and precipitation mechanisms that generate annual floods in this region have not been described in detail. We analyzed a set of long-term annual flood records at climate-sensitive stream gauges across the region and classified the synoptic climatology of each annual flood, quantitatively describing the precipitation mechanisms, and characterize flood seasonality. We find that annual floods here are dominantly generated by Great Lakes-sourced storms and Coastal lows, known locally as ‘nor’easters.’ Great Lakes storms tend to be associated with lower magnitude annual floods (<75th percentile) and Coastal lows are more clearly associated with higher magnitude events (>75th percentile). Tropical cyclones account for few of all annual floods, including extreme events, despite causing some of the region’s largest and most destructive floods. Late winter/early spring is when the greatest number of annual floods occur region wide, and rainfall is the dominant flood-producing mechanism. Rainfall in combination with snowmelt is also important. Both mechanisms are expected to be impacted by projected regional climate change. We find little evidence for associations between flood-producing synoptic storm types or precipitation mechanisms and large-scale atmospheric circulation indices or time periods, despite upward trends in New England annual flood magnitudes. To more completely investigate such associations, partial duration flood series that include more floods than just the largest of each year, and their associated synoptic climatologies and precipitation mechanisms, should be analyzed.