Surface melting is a major component of the Greenland ice
sheet surface mass balance, and it affects sea level rise through direct runoff
and the modulation of ice dynamics and hydrological ...processes,
supraglacially, englacially and subglacially. Passive microwave (PMW)
brightness temperature observations are of paramount importance in studying
the spatial and temporal evolution of surface melting due to their long
temporal coverage (1979–present) and high temporal resolution (daily).
However, a major limitation of PMW datasets has been the relatively coarse
spatial resolution, which has historically been of the order of tens of kilometers.
Here, we use a newly released PMW dataset (37 GHz, horizontal polarization)
made available through a NASA “Making Earth System Data Records for Use in
Research Environments” (MeASUREs) program to study the spatiotemporal
evolution of surface melting over the Greenland ice sheet at an enhanced
spatial resolution of 3.125 km. We assess the outputs of different detection
algorithms using data collected by automatic weather stations (AWSs) and
the outputs of the Modèle Atmosphérique Régional (MAR) regional climate model. We found that sporadic
melting is well captured using a dynamic algorithm based on the outputs of
the Microwave Emission Model of Layered Snowpack (MEMLS), whereas a fixed
threshold of 245 K is capable of detecting persistent melt. Our results
indicate that, during the reference period from 1979 to 2019 (from 1988 to 2019),
surface melting over the ice sheet increased in terms of both duration, up
to 4.5 (2.9) d per decade, and extension, up to 6.9 % (3.6 %) of the
entire ice sheet surface extent per decade, according to the MEMLS
algorithm. Furthermore, the melting season started up to 4.0 (2.5) d
earlier and ended 7.0 (3.9) d later per decade. We also explored the
information content of the enhanced-resolution dataset with respect to the
one at 25 km and MAR outputs using a semi-variogram approach. We found
that the enhanced product is more sensitive to local-scale processes, thereby
confirming the potential of this new enhanced product for monitoring surface
melting over Greenland at a higher spatial resolution than the historical
products and for monitoring its impact on sea level rise. This offers the
opportunity to improve our understanding of the processes driving melting,
to validate modeled melt extent at high resolution and, potentially, to
assimilate these data in climate models.
Abstract
This work presents a novel, spatially distributed, GIS-based application of Benfratello's conceptual method (developed in the 1960s) to estimate the climatic water deficit and the irrigation ...deficit at the field and basin scales. Explicit analytical relationships are obtained to define the deficit uncertainty on the basis of the interannual variability of temperature and precipitation. With this model, we aim at proposing a rather simple and effective tool to deal with the complicated issues of assessing the soil water balance, determining the irrigation deficit and managing the water resources in semiarid agricultural environments, in the context of climatic, land-use and anthropogenic changes. In order to test this new application, the model was applied to estimate the irrigation deficit of the Bonifica della Capitanata consortium in the Apulia region, one of the most important agricultural districts in Southern Italy and in the whole Mediterranean area, in four different historical land-use scenarios. The first results of the application seem encouraging, as by using a limited amount of parameters we estimated an irrigation demand which is in agreement with the irrigation volumes supplied by the consortium. The different land-use cases are discussed in the light of an application of the Budyko curve.
Precipitation measurements by rain gauges are usually affected by a systematic underestimation, which can be larger in case of snowfall. The wind, disturbing the trajectory of the falling water ...droplets or snowflakes above the rain gauge, is the major source of error, but when tipping-bucket recording gauges are used, the induced evaporation due to the heating device must also be taken into account. Manual measurements of fresh snow water equivalent (SWE) were taken in Alpine areas of Valtellina and Vallecamonica, in Northern Italy, and compared with daily precipitation and melted snow measured by manual precipitation gauges and by mechanical and electronic heated tipping-bucket recording gauges without any wind-shield: all of these gauges underestimated the SWE in a range between 15% and 66%. In some experimental monitoring sites, instead, electronic weighing storage gauges with Alter-type wind-shields are coupled with snow pillows data: daily SWE measurements from these instruments are in good agreement. In order to correct the historical data series of precipitation affected by systematic errors in snowfall measurements, a simple ‘at-site’ and instrument-dependent model was first developed that applies a correction factor as a function of daily air temperature, which is an index of the solid/liquid precipitation type. The threshold air temperatures were estimated through a statistical analysis of snow field observations. The correction model applied to daily observations led to 5–37% total annual precipitation increments, growing with altitude (1740 ÷ 2190 m above sea level, a.s.l.) and wind exposure. A second ‘climatological‘ correction model based on daily air temperature and wind speed was proposed, leading to errors only slightly higher than those obtained for the at-site corrections.
Extreme streamflow nonstationarity has probably attracted more attention than mean streamflow nonstationarity in the assessment of the impacts of climate change on the water cycle. Nonetheless, a ...significant decrease in mean streamflow could lead to conditions of scarcity of freshwater in the long-term period, seriously compromising the sustainability of the demand for civil, agricultural, and industrial uses. Regional analyses are useful to better characterize an area’s nonstationarity, since a clear trend at a global scale has not been detected yet. In this article, long-term and high-quality series of streamflow discharges observed in five rivers in the Central Italian Alps, including two multicentury series and two new precipitation and streamflow series not analyzed before, are investigated to statistically characterize individual trends of mean annual runoff volumes. Nonparametric pooled statistics are also introduced to assess the regional trend. Additional climatic and nonclimatic factors, namely, precipitation trends and land cover transformations, have also been considered as potential change drivers. Unlike precipitation, runoff volumes show a marked and statistically significant decrease of −1.45 mm/year, which appears to be homogeneous in the region. The land cover transformation analysis presented here revealed extensive woodland expansions of 510 km2 in 2018 out of the 2650 km2 area measured in 1954, representing 38% of the area investigated in this study: this anthropic driver of enhanced hydrologic losses can be recognized as an additional likely cause for the regional runoff volume decrease.
Basin hydrology is related to the soil–atmosphere interaction driven by several blended processes constrained by the space–time variability of precipitation and soil moisture, along with overland ...flow and flood routing in natural channels. The emerging technologies for the monitoring and prediction of the spatial and temporal distribution of rainfall and soil moisture over a catchment, as well as the hillslope and river runoff, are of considerable interest to predict the hydrological responses of a catchment. In this context, this Special Issue, with its eleven theoretical and applied contributions, aims to shed light on the more recent advances in ground observations and remote sensing products, as well as on the benefits resulting from the integration of technological innovation and the development of new ideas in hydrology science. To this purpose, the accepted articles, written by leading researchers in their field, are intended to present and discuss experimental analyses at the catchment scale in terms of: a) intensive measurement campaigns of soil moisture by in situ sensors, remote sensing and modelling approaches; b) discharge monitoring also for high floods, by leveraging advanced technology for ground surface velocity measurements and spaceborne observations of water surface elevation, river width and slope; c) solid precipitation-measuring methods and the selection of snow gauge stations by merging meteorological, hydrological and remote sensing datasets; d) changes in daily precipitation of different intensities over large river basins along with the identification of the space–time rainfall field for different climatic regions ; and finally e) spatial evaporation patterns in different climate regions and assessment of the dominant climate factors affecting the evaporative demand of the atmosphere. Hopefully this Special Issue provides different useful insights into advancements in emerging technologies for the monitoring of key hydrological variables and will support the design of a scalable system of operational tools leading to suitable flood mitigation measures and reliable real-time warning systems.
Climate-induced changes in small watersheds are still not well researched because long-term datasets are usually missing for these watersheds. Such studies can, however, improve our understanding of ...the watershed response to climatic changes at such a small scale being transparent. In this study, we investigate trends in temperature, precipitation and river-flow characteristics in a small watershed, typical for Central Poland, with 53 years of observations (1963–2015) using the Mann-Kendall test. Particularly, we examine whether any trends in hydro-meteorological variables can be identified, and if any associated changes in water resources in this region can already be observed. We found that this short period already allows for detecting some changes in hydro-meteorological variables. These changes could be characterized by a significant increase in the mean annual air temperature on a daily basis, and a significant decrease in the mean annual discharge on a daily basis and in the minimum annual discharge on a daily basis. Yet, no significant trend could be detected for the total annual precipitation, the maximum summer rainfall, and the maximum annual discharge on a daily basis. These findings indicate that water resources are decreasing in this region, which affects natural habitats, agriculture and local communities.
Hydraulic risk maps provide the baseline for land use and emergency planning. Accordingly, they should convey clear information on the potential physical implications of the different hazards to the ...stakeholders. This paper presents a vulnerability criterion focused on human stability in a flow specifically devised for rapidly evolving floods where life, before than economic values, might be threatened. The human body is conceptualized as a set of cylinders and its stability to slipping and toppling is assessed by forces and moments equilibrium. Moreover, a depth threshold to consider drowning is assumed. In order to widen its scope of application, the model takes the destabilizing effect of local slope (so far disregarded in the literature) and fluid density into account. The resulting vulnerability classification could be naturally subdivided in three levels (low, medium, and high) that are limited by two stability curves for children and adults, respectively. In comparison with the most advanced literature conceptual approaches, the proposed model is weakly parameterized and the computed thresholds fit better the available experimental data sets. A code that implements the proposed algorithm is provided.
Key Points:
An improved physically based model of human stability in a flow is proposed
Reduction of stability due to sloping terrain and fluid density is accounted
The model best matches the available literature experimental data sets
This study presents monitoring data of a debris flow event in the Central Italian Alps. The debris flow occurred on August 16, 2021 in the Blè basin (Val Camonica valley, Lombardia Region) and was ...recorded by a monitoring station installed just few weeks before. The monitoring system was deployed to document the hydrologic response of the catchment to rainfall, and was designed to be lightweight, relatively cheap, and easy to deploy in the field. To this purpose, we combined video cameras with geophysical sensors (geophones and infrasound) and optimized the power supply system. The data recorded during the event allowed to identify the triggering rainfall, document the flow behaviour, and estimate surface flow velocity and flow rate using Particle Image Velocimetry algorithms. Moreover, the seismic signal generated by the debris flow revealed a peculiar frequency spectrum compared to regular streamflow. These results show that even a relatively simple monitoring system may provide valuable data on real debris flow events.
Mammal bioerosion is an emergent threat to the functionality of levees. In the present paper, the problem of assessing the failure probability of levees affected by mammal bioerosion is addressed. A ...fully bivariate description of peak flow discharge and flood duration is combined with a deterministic unsteady seepage flow model to obtain a suitable model of variably disturbed levee response to the observed natural variability of floods. Monte Carlo analysis is also implemented to evaluate the epistemic uncertainty connected to the description of the river system. The obtained model is tested with respect to a real‐world levee located along the Secchia River in northern Italy, which underwent a disastrous failure caused by mammal bioerosion in 2014. The convex linear combination of two Archimedean copulas is found to fit the empirical dependence structure between peak flow discharge and flood duration. The reliability of the unsteady seepage flow model is tested against detailed numerical simulations of the seepage occurring through the levee body. A limit state function is obtained by comparing the maximum extent of the seepage front to the distance between the den end and the riverside levee slope, and the corresponding levee safety and failure regions are delimited. Results obtained from the developed model reveal a significant impact of mammal dens located near the levee crest in terms of failure probability and related return period. This impact is consistent with failures observed in the study area.
Plain Language Summary
Burrowing mammals often find in levees a suitable habitat. Unfortunately, mammal dens can significantly compromise the functionality of levees by creating preferential flow paths for flood water seeping through the levee bodies, and by causing ultimately levee failures due to excessive seepage and internal erosion. In fact, many levee failures have been connected to the levee weakening caused by mammal dens. Mammal bioerosion significantly increases the failure probability of levees and the related flood risk in densely populated floodplains. Estimating the failure probability of levees affected by mammal bioerosion is therefore a relevant societal need. In the present study levee, safety and failure conditions are estimated by combining a fully bivariate statistical description of peak flow discharge and flood duration with a computationally efficient unsteady seepage flow model. The resulting modeling framework incorporates the natural variability of floods and the essential hydraulic properties of disturbed/undisturbed levees. Model results reveal that the return period of levee failure due to excessive seepage reduces from 100 to 9 years, namely of −91%, when the mammal den extends for 84% of levee thickness. These results can be used to inform levee design and maintenance programs for the safety of societies living in floodplains worldwide.
Key Points
Fully bivariate analysis of peak flow discharge and flood duration is used to describe the hydrologic forcing to levees
Vorogushyn et al.’s unsteady seepage flow model is extended to derive the failure probability of variably disturbed levees
Return period of levee failure due to excessive seepage reduces from 100 to 9 years when the mammal den extends for 84% of levee thickness
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