Hydroclimatic Indicators Research Articles

Understanding the variability of large-scale statistical downscaling methods under different climate regimes

Large-scale downscaling plays an important role in assessing global impacts on hydrological sphere due to climate changes. In such downscaling efforts, it is essential to consider the various climate regimes. Although previous studies have indirectly suggested that the accuracy of downscaling might differ among climate regimes, research that systematically understands or quantifies the variability of this accuracy remains scarce. This study addresses this gap by systematically quantifying the performance of five different large-scale downscaling methods across various climate regimes in the context of downscaling hydroclimatic indicators. Our findings indicate that large-scale downscaling yields the highest accuracy on average when applied to temperature, precipitation, and runoff in tropical, arid, and temperate climate regimes, respectively, while showing poor accuracy in polar regimes for all variables. The maximum difference of normalized root mean squared errors for hydroclimate indicators is 69 % across climate zones, and the spatial distribution of downscaling accuracy aligns with spatial distribution of climate zones. The variation of downscaling accuracy is particularly significant in temperature, precipitation, and seasonal runoff indicators. Furthermore, linkages between accuracy of climate and hydrological indicators differ by climate zones. The underlying reasons for the different accuracy of downscaling are spatially different accuracy of global climate models (GCMs) and interaction of downscaling structure and climate regimes. This study articulated the source of spatially different accuracy/uncertainties for large-scale downscaling that have never been addressed before. The findings of this study provide valuable support in selecting appropriate downscaling methods, ultimately enhancing the spatial reliability and accuracy of large-scale downscaling methods.

Dryland hydroclimatic response to large tropical volcanic eruptions during the last millennium

Drylands are highly vulnerable to climate change due to their fragile ecosystems and limited ability to adapt. In contrast to the global drying after tropical volcanic eruptions shown previously, we demonstrate that large tropical volcanic eruptions can induce significant two-year hydroclimatic wetting over drylands by employing the last millennium simulations. During this wetting period, which extends from the first to the third boreal winter after the eruption, several hydroclimatic indicators, such as self-calibrating Palmer Drought Severity Index based on the Penman-Monteith equation for potential evapotranspiration (scPDSIpm), standard precipitation evapotranspiration index (SPEI), aridity index (AI), top-10cm soil moisture (SM10cm), and leaf area index (LAI), show significant positive anomalies over most drylands. The primary contribution to the wetting response is the potential evapotranspiration (PET) reduction resulting from dryland surface cooling and reduced solar radiation, as well as a weak contribution from increased precipitation. The latter is due to the wind convergence into drylands caused by slower tropical cooling compared to drylands. The wetting response of drylands to volcanic eruptions also demonstrates some benefits over the global hydrological slowdown resulting from stratospheric aerosol injection, which replicates the cooling effects of volcanic eruptions to address global warming.

An interactive system to map land degradation and inform decision‐making to achieve land degradation neutrality via convergence of evidence across scales: A case‐study in Ecuador

AbstractOne of the core challenges to achieve land degradation neutrality (LDN) is to spatially identify, and strategically prioritise, the areas to implement actions to avoid, reduce and reverse land degradation. To achieve this, a tool for a participatory and data‐driven assessment considering both the biophysical and socio‐economic dimensions of land degradation across scales was developed for Ecuador. In this paper, we present the methodology and results obtained, including the spatially explicit interactive tool developed to integrate indicators that support the scaling‐up of sustainable land management (SLM). The process involved specialists from various national and international institutions, as well as decision makers from the public sector and other relevant stakeholders. Cloud computing allowed the integration of five main sources of data: (1) the results of a participatory land degradation assessment based on an expert knowledge questionnaire following the land degradation assessment in drylands (LADA) and world overview of conservation approaches and technologies (WOCAT) methodology; (2) the Hand‐in‐Hand Initiative Ecuador typology maps based on poverty and estimated agricultural potential and efficiency scores from household surveys; (3) National datasets on land cover and land use, soil properties, and hydro climatic indicators; (4) global satellite‐derived LDN indicators, such as land productivity dynamics; and (5) documented SLM practices from WOCAT Global SLM Database. The tool is based on a Google Earth Engine application and allows decision makers to easily compare results and obtain statistics at different spatial scales and landscapes, including land use systems delimited by experts. It also includes a multi‐criteria module to identify areas with specific characteristics to prioritise different types of interventions to achieve the Country's LDN targets. Convergence of local and global evidence allowed the identification of hotspots of degradation as well as areas of false positives/negatives—if only global or remote sensing indicators were considered. The participatory process contributed to strengthening multi‐sector cooperation mechanisms and to guaranteeing ownership of the tool and the results. The system will support Ecuador's efforts to monitor and report progress towards LDN to the United Nations Convention to Combat Desertification. The system's code is shared as a repository at Earth Engine and can be adapted to and used by other countries and regions.

Hydrological and botanical diversity of a raised bog and its evaluation using in situ and remote sensing methods

Peatland vegetation requires water-logged conditions for peat-forming plant communities to survive. Changes in water regimes have been found to alter the soil environment and cause shifts in species composition. Occasionally, the spatial and chronological constraints in water table monitoring impede the correct evaluation of the status of these sensitive ecohydrological systems. Therefore, it is important to combine in situ and remote sensing methods to assess ecohydrological diversity over large areas of threatened peatland ecosystems. The present study assessed the relationship between hydrological indicators (the in situ water table fluctuations of 57 measurement wells and five study plots in the 2019 and 2020 growing seasons); botanical indicators (in situ species composition in three raised bog habitat types, namely, bog woodland, a semi-open raised bog, and an open raised bog); and spectral indices (NDVI – Normalised Difference Vegetation Index and NDWI – Normalised Difference Water Index, 2015–2020, Sentinel 2) for the evaluation of heterogeneous raised bog spatial patterns and temporal change. There were statistically significant relationships between vegetation and water table depth in different raised bog habitat types. Deeper water tables prevailed in woodland habitats (trees, green mosses, Rhododendron tomentosum) and vice versa in areas where open raised bog plants (Sphagnum) occupied the surface. Moderate relationships (r > |0.4|, p <.05) were detected between some of the botanical and hydrological indicators and spectral indices. The application of high-resolution remote sensing data may be useful for raised bog measurements, and changes in vegetation cover and related spectral indices may become hydroclimatic indicators.

Genesis of wavy carbonate flowstone deposits in Bossea Cave (North Italy) and their hydroclimatic significance

Speleothems show an array of shapes. Flowstones are commonly tabular sheet-like deposits, which cover cave floors and walls. They can procure detailed information about past hydrogeological conditions through their morphology, geochemical composition and stratigraphic properties, which in turn are related to the climate conditions at the surface. This is possible if the climate and environmental factors controlling the formation of these deposits are well understood. In Bossea Cave (north-east Italy), we have investigated highly symmetrical wavy flowstones that have never been described in detail before. These deposits show a cyclical repetition of sloped and sub-vertical layers, with knickpoints migrating downslope. This paper investigates the origin of these peculiar carbonate deposits, using: i) terrestrial laser scanning surveys; ii) petrographic observations; iii) oxygen and carbon stable isotope analyses; iv) hydrochemical monitoring data of feeding waters. According to these analyses, we have generated a genetic model that demonstrates: 1) laminar flow of CaCO3–rich water prevails during the deposition of the flowstone; in accordance, the final flowstone architecture does not appear to be influenced by random irregularities of the underlying bedrock substrate. 2) The peculiar morphology is inherited by ripples occurring in the flowing water films during carbonate deposition, which trigger the precipitation of regularly spaced CaCO3 deposits along the bedrock slopes. Because of these ripple-induced initial deposits, calcite then deposits as sloped and sub-vertical layers, giving rise to a wavy-like morphology. 3) Wavy calcite layers are only deposited after heavy rainfall events occurred within two to four consecutive rainy days (10 to 20 mm/hour during rainfall peaks; average rates between 3.5 and 7.0 mm/hour); in contrast, calcite deposition cannot occur during low rainfall events (less than 5 mm/hour during rainfall peaks, average rates around 0.8 mm/hour). We therefore propose that the studied wavy flowstones are hydroclimatic indicators, testifying the occurrence of flashy type recharge related to heavy rainfall events. Similar deposits could record these same hydro-climatic conditions in other karst areas.In recent decades, storms have caused more frequent flooding in highly populated Mediterranean areas, especially in Italy. Wavy flowstones may offer a new archive to gain a better understanding of the long-term dynamics of intense precipitation events and, thus, help to improve future climate scenarios.

Examining evaporative demand and water availability in recent past for sustainable agricultural water management in India at sub-basin scale

This study explores recent changes in evaporative demand and water availability across 100 river sub-basins in India by partitioning the actual evapotranspiration (AET) into green water evapotranspiration (ET-Green) and blue water evapotranspiration (ET-Blue). For computation of ET-Green and ET-Blue, the Budyko framework is applied to long-term scenario (2003–2017) and to intra-annual averaged series (i.e. 2003-2007, 2008–2012 and 2013–2017). For the Budyko analysis, the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS), Global Land Data Assimilation System (GLDAS) AET and Climate Research Unit Global Data Assimilation System (CRU GDAS) Potential ET (PET) climate forcing variables have been utilized. Multiple hydro-climatic indicators, such as dryness index (DI), evaporative index (EI), and responsivity with respect to theoretical Budyko curve are computed and they show substantial variations across sub-basins from far past time (2003) to recent past (2017). The changes in DI and EI highlight the diversity in evaporative demand and dryness condition across the country. Results reveal that India's evaporative water demand is largely influenced by ET-Green (up to 65%) that depends mainly on precipitation. At the same time, in many river sub-basins, ET-Blue that depends on external sources of water like diversion or stored water, is significant. The shape parameter (ω) of Fu's Budyko equation, that can be utilized for the future assessment of ET-Green and ET-Blue, has been optimized. The results of this study would of immense value for sustainable irrigation water management and improving water use efficiency in agriculture and overall water availability in river basins in India.

Projecting armed conflict risk in Africa towards 2050 along the SSP-RCP scenarios: a machine learning approach

In the past decade, several efforts have been made to project armed conflict risk into the future. This study broadens current approaches by presenting a first-of-its-kind application of machine learning (ML) methods to project sub-national armed conflict risk over the African continent along three Shared Socioeconomic Pathway (SSP) scenarios and three Representative Concentration Pathways towards 2050. Results of the open-source ML framework CoPro are consistent with the underlying socioeconomic storylines of the SSPs, and the resulting out-of-sample armed conflict projections obtained with Random Forest classifiers agree with the patterns observed in comparable studies. In SSP1-RCP2.6, conflict risk is low in most regions although the Horn of Africa and parts of East Africa continue to be conflict-prone. Conflict risk increases in the more adverse SSP3-RCP6.0 scenario, especially in Central Africa and large parts of Western Africa. We specifically assessed the role of hydro-climatic indicators as drivers of armed conflict. Overall, their importance is limited compared to main conflict predictors but results suggest that changing climatic conditions may both increase and decrease conflict risk, depending on the location: in Northern Africa and large parts of Eastern Africa climate change increases projected conflict risk whereas for areas in the West and northern part of the Sahel shifting climatic conditions may reduce conflict risk. With our study being at the forefront of ML applications for conflict risk projections, we identify various challenges for this arising scientific field. A major concern is the limited selection of relevant quantified indicators for the SSPs at present. Nevertheless, ML models such as the one presented here are a viable and scalable way forward in the field of armed conflict risk projections, and can help to inform the policy-making process with respect to climate security.

Spatio-temporal analysis of leptospirosis incidence and its relationship with hydroclimatic indicators in northeastern Argentina

Leptospirosis is considered the most globally widespread zoonotic illness; it has been classified as an emerging or reemerging infectious disease by the World Health Organization. Leptospirosis is a disease caused by a pathogenic spirochete of the genus Leptospira. The infection occurs by contacting with the urine of animal reservoirs or contaminated environments. Leptospirosis can be controlled by vaccines used mainly in animals, antibiotics given to exposed humans, and flood-affected people moved to a safe place. Northeastern Argentina accounts for the highest annual number of cases and deaths due to leptospirosis of the country. This interdisciplinary study aims to analyze the spatial and temporal distribution of leptospirosis, and assesses the hydroclimatic factors that give rise to the outbreaks in northeastern Argentina. The main goal is to detect the hydroclimatic indicators that can influence leptospirosis outbreaks occurrence in the northeastern Argentina. We perform a spatio-temporal analysis of the leptospirosis in the provinces of Santa Fe and Entre Ríos to distinguish the regions, years and seasons with the highest incidence of this disease. This study analyzes confirmed cases of leptospirosis between 2009 and 2018 years. Hydroclimatic indicators (monthly total precipitation, monthly river hydrometric level and Oceanic Niño Index) associated with outbreaks of leptospirosis vary in different spatial scales (provincial, departmental and cities). In the last outbreak of leptospirosis in 2015–2016 the number of cases was lower than expected. This could have been a consequence of increased prophylaxis in that flood event. Therefore, this is a variable that should be incorporated in future studies.

Future Hydroclimatic Impacts on Africa: Beyond the Paris Agreement.

Projections of global warming in Africa are generally associated with increasing aridity and decreasing water availability. However, most freshwater assessments focus on single hydroclimatic indicators (e.g., runoff, precipitation, or aridity), lacking analysis on combined changes in evaporative demand, and water availability on land. There remains a high degree of uncertainty over water implications at the basin scale, in particular for the most water‐consuming sector—food production. Using the Budyko framework, we perform an assessment of future hydroclimatic change for the 50 largest African basins, finding a consistent pattern of change in four distinct regions across the two main emission scenarios corresponding to the Paris Agreement, and the business as usual. Although the Paris Agreement is likely to lead to less intense changes when compared to the business as usual, both scenarios show the same pattern of hydroclimatic shifts, suggesting a potential roadmap for hydroclimatic adaptation. We discuss the social‐ecological implications of the projected hydroclimatic shifts in the four regions and argue that climate policies need to be complemented by soil and water conservation practices to make the best use of future water resources.

The Functioning of the Cascade Lithodynamic System of the Kuda River Basin (Upper Angara Region)

The redistribution of sediments in the Kuda river basin as a result of erosion-accumulation processes is investigated from the systems perspective. The current geodynamic position of the basin associated with the transition zone from the Siberian platform to the Baikal rift is emphasized. The contribution of cryogenic, karst and aeolian processes to the mobilization of matter in the system is considered. A quantitative assessment of the amount of transported material in the upper (slope), middle (ravine) and lower (riverbed) lithodynamic zones of the basin was made. Time series of the main hydroclimatic indicators were used to determine the long-term dynamics of the functioning of the basin. Using the satellite images, we identified changes in the economic activities within the basin over the past 30 years. They imply a reduction in croplands and an expansion of grasslands. Calculations show that the annual volume of sediments transported within the basin reaches 3 184 430 tons. Most of them (89%) are involved in the movement by the runoff of storm water, and only 364 405 tons are transported with the runoff of melt water. The role of gully erosion in ablation and sediment transportation is insignificant, because most of the gullies are inactive with a reduction in agriculture; the average growth rate of the heads of gullies does not exceed 0.5 m/year. Channel processes contribute primarily to the redistribution of sediments between adjacent sections of the channel, and their transport to large distances is limited by karst processes and by a significant anthropogenic transformation of the bottoms of the valleys. The annual flow of suspended and transported sediments is a mere 31 000 tons, and the main ablation of material from the system occurs in a dissolved form. In general, the mechanical volume of sediment yield from the system makes up 1%. The rest of material is redistributed in the basin and causes an enhanced accumulation. It is shown that almost half of the sediments is intercepted by large ponds; the rest is accumulated in the bottoms of the valleys in areas with active karst development, on floodplains as well as in talus and proluvial trains. The study determined a general trend in the transformation of the relief as a result of the functioning of the basin implying its planation.

Are Glacials Dry? Consequences for Paleoclimatology and for Greenhouse Warming

Past cold climates are often thought to have been drier than today on land, which appears to conflict with certain recent studies projecting widespread terrestrial drying with near-future warming. However, other work has found that, over large portions of the continents, the conclusion of future drying versus wetting strongly depends on the physical property of interest. Here, it is shown that this also holds in simulations of the Last Glacial Maximum (LGM): the continents have generally wetter topsoils and higher values of common climate wetness metrics than in the preindustrial, as well as generally lower precipitation and ubiquitously lower photosynthesis (likely driven by the low CO2), with streamflow responses falling in between. Using a large existing global pollen and plant fossil compilation, it is also confirmed that LGM grasslands and open woodlands grew at many sites of present-day forest, seasonal forests at many sites of present-day rain forest, and so forth (116–144 sites out of 302), while changes in the opposite sense were very few (9–17 sites out of 302) and spatially confined. These vegetation changes resemble the model photosynthesis responses but not the hydroclimate responses, while published lake-level changes resemble the latter but not the former. Thus, confidence in both the model hydrologic and photosynthesis projections is increased, and there is no significant conflict. Instead, paleo- and modern climate researchers must carefully define “wetting” and “drying” and, in particular, should not assume hydrologic drying on the basis of vegetation decline alone or assume vegetation stress on the basis of declines in hydroclimatic indicators.

How does the North Atlantic Oscillation affect the water levels of the Great Lakes with regard to hydro-climatic indicators?

In this study, the changes of long-term mean annual water levels of the Great Lakes in North America are investigated, including the potential impacts of the North Atlantic Oscillation (NAO). The levels of Lakes Superior, Michigan-Huron, St. Clair, Erie and Ontario and the hydro-climatic data, such as precipitation, evaporation and runoff, are evaluated together in view of the influence of NAO. The changes in the lake levels and hydro-climatic indicators are analysed. The annual hydro-climatic data, annual mean lake levels and the NAO indices are nondimensionalized through the nonparametric Mann-Kendall test. Then, the sequential Mann-Kendall test and paired t test are performed to gain insight into the trends of the time series and possible turning points. As a result of this study, the trend direction changes for all of the lakes are determined in the years 1965 and 1987, based on the records of the last 95 years. A similar tendency for evaporation, precipitation and runoff is found in 1982, 1935 and 1965. Regarding the effect of North Atlantic Oscillation on the changes of the lake levels, the same directional variations are found between the lake levels and the NAO FMA (February-March-April) indices. However, the directional variations between the lake levels and NAO JJA (June-July-August) indices are reversed. The absolute values of the correlation coefficients increase from west to east (from Lake Superior to Lake Ontario).

Patterns of regional hydroclimatic shifts: An analysis of changing hydrologic regimes

AbstractTemporal shifts in precipitation and runoff regime curves appear throughout the continental United States, but differ from region to region. This paper explores these regime shifts by building upon a hydroclimatic classification system that partitions the United States into clusters of similarly behaved catchments using four simple hydroclimatic indicators. Hydroclimate data from over four hundred catchments over a 55 year period (belonging to the MOPEX data set) are analyzed to reveal how the indicators have shifted before and after 1970, before and after 1975, and before and after 1980. Statistically significant hydroclimatic changes in these indicators are explored qualitatively, suggesting which catchments today might resemble other catchments tomorrow. Thus, a preview of current locations in one class under future conditions is provided by observing existing locations of another class. The classification system structure enables organization of these data, allowing patterns of regime change to emerge without highly specified models at each individual site. Regional analyses explore changes in mean seasonal precipitation/runoff regimes, including shifts in the daily variability of precipitation and runoff. Additionally, changes in regime curves of minimum and maximum precipitation/runoff observations are analyzed and discussed. Results indicate that after 1980, classifications typically found in the southeastern quarter of the United States have expanded northward and westward. Regionally, the Midwest and Rocky Mountains seem to demonstrate more frequent, but less intense storms after 1980, while southeastern catchments receive much less water in the form of precipitation and runoff than in previous years.

Climate-driven trends in mean and high flows from a network of reference stations in Ireland

This paper introduces a reference hydrometric network for Ireland and examines the derived flow archive for evidence of climate-driven trends in mean and high river flows. The Mann-Kendall and Theil-Sen tests are applied to eight hydroclimatic indicators for fixed and variable (start and end date) records. Spatial coherence and similarities of trends with rainfall suggest they are climate driven; however, large temporal variability makes it difficult to discern widely-expected anthropogenic climate change signals at this point in time. Trends in summer mean flows and recent winter means are at odds with those expected for anthropogenic climate change. High-flow indicators show strong and persistent positive trends, are less affected by variability and may provide earlier climate change signals than mean flows. The results highlight the caution required in using fixed periods of record for trend analysis, recognizing the trade-off between record length, network density and geographic coverage. Editor Z.W. Kundzewicz; Associate editor H. Lins Citation Murphy, C., Harrigan, S., Hall, J., and Wilby, R.L., 2013. Climate-driven trends in mean and high flows from a network of reference stations in Ireland. Hydrological Sciences Journal, 58 (4), 755–772.

Relationships between Recent Pan-Arctic Snow Cover and Hydroclimate Trends

AbstractUsing the Variable Infiltration Capacity (VIC) land surface model forced with gridded climatic observations, the authors reproduce spatial and temporal variations of snow cover extent (SCE) reported by the National Oceanic and Atmospheric Administration (NOAA) Northern Hemisphere weekly satellite SCE data. Both observed and modeled North American and Eurasian snow cover in the pan-Arctic have statistically significant negative trends from April through June over the period 1972–2006. To diagnose the causes of the pan-Arctic SCE recession, the authors identify the role of surface energy fluxes generated in VIC and assess the relationships between 15 hydroclimatic indicators and NOAA SCE observations over each snow-covered sensitivity zone (SCSZ) for both North America and Eurasia. The authors find that surface net radiation (SNR) provides the primary energy source and sensible heat (SH) plays a secondary role in observed changes of SCE. As compared with SNR and SH, latent heat has only a minor influence on snow cover changes. In addition, these changes in surface energy fluxes resulting in the pan-Arctic snow cover recession are mainly driven by statistically significant decreases in snow surface albedo and increased air temperatures (surface air temperature, daily maximum temperature, and daily minimum temperature), as well as statistically significant increased atmospheric water vapor pressure. Contributions of other hydroclimate variables that the authors analyzed (downward shortwave radiation, precipitation, diurnal temperature range, wind speed, and cloud cover) are not significant for observed SCE changes in either the North American or Eurasian SCSZs.

Long‐term records of dissolved organic carbon flux from peat‐covered catchments: evidence for a drought effect?

AbstractThis study considers three long records of dissolved organic carbon (DOC) flux from two catchments with peat‐covered headwaters. The catchments vary in size from 11 to 818 km2 and the records are at least 12 years old, with one record going back to 1965. The study compares both annual and monthly DOC flux records with a range of hydroclimatic indicators in order to test which component of droughts may contribute to increasing DOC flux. The study found that: (1) there was no significant correlation between any of the proposed drought variables and DOC flux in any of the study catchments over periods of up to 34 years; (2) the most important variable for explaining the DOC flux was the runoff from the catchments overlying a seasonal cycle and an underlying upward trend was present in some records; (3) the residual time‐series, after removal of the best‐fit models, showed no evidence of increased production after times of severe drought. The lack of any evidence for any additional biogeochemical reactions associated with drought supports evidence that DOC loss from peat is limited by its solubility and that its production is fast on the time‐scale of runoff events. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Drought Management Planning with Economic and Risk Factors

Traditional drought management planning has focused on curtailing demand through various conservation measures when regional hydroclimatic indicators reach specific trigger levels. This study suggests a methodology that can augment traditional drought management methods in two ways. First, regional hydroclimatic indicators, which are not necessarily indicative of the impacts of droughts on individual water storage systems, are replaced with system specific indicators in the context of supply reliability, or likelihood of system failure. Second, the study illustrates how economically optimal programs for conjunctive supply and demand management can be developed once the susceptibility of a specific water supply system to drought conditions is quantitatively understood. The method links a stochastic simulation program with a mixed-integer linear program aimed at achieving target levels of supply reliability at minimum economic cost. Results from a case study in Western Massachusetts were used to guide capit...