Sub-daily Timescales Research Articles

Noise Characteristics of High‐Rate Multi‐GNSS for Subdaily Crustal Deformation Monitoring

AbstractHigh‐rate GPS (Global Positioning System) has the potential to record crustal motions on a wide subdaily timescale from seconds to hours but usually fails to capture subtle deformations which are often overwhelmed by the centimeter noise of epoch‐wise GPS displacements. We hence investigated high‐rate multi‐GNSS (Global Navigation Satellite System) by processing 1 Hz GPS/GLONASS/BeiDou data at 15 static stations over 24 days and also those from the 8 August 2017 Jiuzhaigou Mw 6.5 earthquake. In contrast to high‐rate GPS, its further integration with GLONASS/BeiDou reduces near uniformly the power spectral densities (PSDs) of 1 Hz displacement noise by 4–6 dB over the periods from a few seconds to half of a day, and orbital repeat time (ORT) filtering on all GNSS further again leads to a 2 more decibel decline of the PSDs over the periods of a few tens of seconds to minutes. BeiDou ORT filtering, however, takes effect mainly on the periods of over 2,000 s due to the high altitudes of Inclined Geosynchronous Satellite Orbiters/Geosynchronous Earth Orbiters. Multi‐GNSS integration is on average as effective as GPS ORT filtering in reducing PSDs for the periods of a few tens of seconds to minutes while desirably can further decrease the PSDs on almost all other periods by 3–4 dB thanks to the enhanced satellite geometry. We conclude that the introduction of more GNSS into high‐rate solutions and its augmentation by ORT filtering benefit the discrimination of slight deformations over a broad subdaily frequency band.

Downscaling future climate change projections over Puerto Rico using a non-hydrostatic atmospheric model

We present results from 20-year “high-resolution” regional climate model simulations of precipitation change for the sub-tropical island of Puerto Rico. The Japanese Meteorological Agency Non-Hydrostatic Model (NHM) operating at a 2-km grid resolution is nested inside the Regional Spectral Model (RSM) at 10-km grid resolution, which in turn is forced at the lateral boundaries by the Community Climate System Model (CCSM4). At this resolution, the climate change experiment allows for deep convection in model integrations, which is an important consideration for sub-tropical regions in general, and on islands with steep precipitation gradients in particular that strongly influence local ecological processes and the provision of ecosystem services. Projected precipitation change for this region of the Caribbean is simulated for the mid-twenty-first century (2041–2060) under the RCP8.5 climate-forcing scenario relative to the late twentieth century (1986–2005). The results show that by the mid-twenty-first century, there is an overall rainfall reduction over the island for all seasons compared to the recent climate but with diminished mid-summer drought (MSD) in the northwestern parts of the island. Importantly, extreme rainfall events on sub-daily and daily time scales also become slightly less frequent in the projected mid-twenty-first-century climate over most regions of the island.

Diel ecosystem conductance response to vapor pressure deficit is suboptimal and independent of soil moisture

Ecosystem conductance, which describes ecosystem regulation of water and carbon exchange and links plant functions with the environment, is a critical component in ecosystem and earth system models. However, the behaviors of ecosystem conductance at the ecosystem level and its responses to environmental conditions are still largely unclear. In this study, half-hourly data of 77 eddy-covariance sites from the FLUXNET2015 dataset were used to compare four ecosystem conductance models at the ecosystem level and determine the most consistent vapor pressure deficit (VPD) dependence across plant functional types for varying soil moisture stress levels at the subdaily time scale. We used leaf-level VPD (VPDl), a better indicator of atmospheric dryness at the leaf level, for canopy-level analysis instead of measured atmospheric VPD. Detection of the best-fitted exponent of VPDl indicates that ecosystem conductance responds to VPD between optimality-theory (i.e., VPD−0.5 dependence) and Leuning’s (i.e., VPD−1 dependence) models. Accounting for different soil moisture stress levels only affected minimum ecosystem conductance and did not affect the exponent and factor of VPDl, indicating limited diurnal soil moisture-VPDl interactions. These results indicate limited interaction between xylem and stomata at subdaily time scales and that soil moisture effects can be simplified as a regulation of minimum (soil plus canopy) conductance.

Role of Convective Precipitation in the Relationship between Subdaily Extreme Precipitation and Temperature

On a subdaily time scale, the intensities of extreme precipitation are observed to increase with temperature at a rate exceeding water vapor constraints determined by the Clausius–Clapeyron (C-C) relationship. This so-called super C-C scaling has been suggested to occur as a result of 1) the statistical effect that involves the transition of precipitation types from stratiform to convective events and 2) the physical effect by which the convective process itself can overcome the thermodynamic limitation. This study examines these two mechanisms for the super C-C relationship using in situ observations in South Korea for a recent 35-yr period, focusing on the role of convective rainfall. Scaling results show that hourly extreme precipitation undergoes a transition from a C-C rate to a super C-C rate at around 20°C, supporting the statistical effect. The transition temperature observed in South Korea is, however, much higher than in European regions (12°C), which seems to be due to the climatologically lower frequency of convective events in South Korea than in Europe. Nevertheless, the threshold fraction of convective precipitation when the scaling transition starts to occur is found to very similar between two regions, around 0.2, indicating the important role of convective events in shaping the scaling. On the other hand, convective extreme precipitation alone exhibits a super C-C scaling, suggesting that the physical effect is also at work in South Korea. Also, the scaling shows a robust peaklike shape with maximum precipitation intensity near 24°C, which is closely linked with moisture limitation at high temperature, supporting the previous findings.

Surface Energy Balance Closure and Turbulent Flux Parameterization on a Mid-Latitude Mountain Glacier, Purcell Mountains, Canada

In the majority of glacier surface energy balance studies, parameterisation rather than direct measurement is used to estimate one or more of the individual heat fluxes, with others, such as the rain and ground heat fluxes, often deemed negligible. Turbulent fluxes of sensible and latent heat are commonly parameterised using the bulk aerodynamic technique. This method was developed for horizontal, uniform surfaces rather than sloped, inhomogeneous glacier terrain, and significant uncertainty remains regarding the selection of appropriate roughness length values, and the validity of the atmospheric stability functions employed. A customised weather station, designed to measure all relevant heat fluxes, was installed on an alpine glacier over the 2014 melt season. Eddy covariance techniques were used to observe the turbulent heat fluxes, and to calculate site-specific roughness values. The obtained dataset was used to drive a point ablation model, and to evaluate the most commonly used bulk methods and roughness length schemes in the literature. Modelled ablation showed good agreement with observed rates at seasonal, daily, and sub-daily timescales, effectively closing the surface energy balance, and giving a high level of confidence in the flux observation method. Net radiation was the dominant contributor to melt energy over the season (65.2%), followed by the sensible heat flux (29.7%), while the rain heat flux was observed to be a significant contributor on daily timescales during periods of persistent heavy rain (up to 20% day-1). Momentum roughness lengths observed for the study surface (snow: 10-3.8 m; ice: 10-2.2 m) showed general agreement with previous findings, while the scalar values (temperature: 10-4.6 m; water vapour: 10-6 m) differed significantly from those for momentum, disagreeing with the assumption of equal roughness lengths. Of the three bulk method stability schemes tested, the functions based on the Monin-Obukhov length returned mean daily flux values closest to those observed, but displayed poor performance on sub-daily timescales, and periods of substantial flux overestimation.

Projections of climate-driven changes in tuna vertical habitat based on species-specific differences in blood oxygen affinity.

Oxygen concentrations are hypothesized to decrease in many areas of the ocean as a result of anthropogenically driven climate change, resulting in habitat compression for pelagic animals. The oxygen partial pressure, pO2 , at which blood is 50% saturated (P50 ) is a measure of blood oxygen affinity and a gauge of the tolerance of animals for low ambient oxygen. Tuna species display a wide range of blood oxygen affinities (i.e., P50 values) and therefore may be differentially impacted by habitat compression as they make extensive vertical movements to forage on subdaily time scales. To project the effects of end-of-the-century climate change on tuna habitat, we calculate tuna P50 depths (i.e., the vertical position in the water column at which ambient pO2 is equal to species-specific blood P50 values) from 21st century Earth System Model (ESM) projections included in the fifth phase of the Climate Model Intercomparison Project (CMIP5). Overall, we project P50 depths to shoal, indicating likely habitat compression for tuna species due to climate change. Tunas that will be most impacted by shoaling are Pacific and southern bluefin tunas-habitat compression is projected for the entire geographic range of Pacific bluefin tuna and for the spawning region of southern bluefin tuna. Vertical shifts in P50 depths will potentially influence resource partitioning among Pacific bluefin, bigeye, yellowfin, and skipjack tunas in the northern subtropical and eastern tropical Pacific Ocean, the Arabian Sea, and the Bay of Bengal. By establishing linkages between tuna physiology and environmental conditions, we provide a mechanistic basis to project the effects of anthropogenic climate change on tuna habitats.

A regional analysis of the impact of dams on water temperature in medium-size rivers in eastern Canada

Various studies have helped gain a better understanding of the thermal impacts of dams on a site-specific basis, but very few studies have compared the thermal impacts of varying types of dams within the same region. In this study, we conducted a regional-scale assessment of the impacts of dams on the thermal regime of 13 medium-size rivers in eastern Canada. The objectives of this study were to identify features of the thermal regime of rivers that are predominantly impacted by dams and to compare the impacts associated with different types of regulation (run-of-river, storage, peaking). The thermal regime of regulated and unregulated rivers was characterized using 15 metrics that described the magnitude, frequency, duration, timing, and rate of change of water temperature. Results indicate that storage and peaking dams impounding at least 10% of the median annual runoff generally (i) reduced the magnitude of water temperature variation at seasonal, daily, and subdaily timescales and (ii) increased the monthly mean water temperature in September. This regional assessment offers important insight regarding a generalized pattern of thermal alteration by dams, and this information could be used to guide biological monitoring efforts in regulated rivers.

Landslides in West Coast metropolitan areas: The role of extreme weather events

Abstract Rainfall-induced landslides represent a pervasive issue in areas where extreme rainfall intersects complex terrain. A farsighted management of landslide risk requires assessing how landslide hazard will change in coming decades and thus requires, inter alia, that we understand what rainfall events are most likely to trigger landslides and how global warming will affect the frequency of such weather events. We take advantage of 9 years of landslide occurrence data compiled by collating Google news reports and of a high-resolution satellite-based daily rainfall data to investigate what weather triggers landslide along the West Coast US. We show that, while this landslide compilation cannot provide consistent and widespread monitoring everywhere, it captures enough of the events in the major urban areas that it can be used to identify the relevant relationships between landslides and rainfall events in Puget Sound, the Bay Area, and greater Los Angeles. In all these regions, days that recorded landslides have rainfall distributions that are skewed away from dry and low-rainfall accumulations and towards heavy intensities. However, large daily accumulation is the main driver of enhanced hazard of landslides only in Puget Sound. There, landslide are often clustered in space and time and major events are primarily driven by synoptic scale variability, namely “atmospheric rivers” of high humidity air hitting anywhere along the West Coast, and the interaction of frontal system with the coastal orography. The relationship between landslide occurrences and daily rainfall is less robust in California, where antecedent precipitation (in the case of the Bay area) and the peak intensity of localized downpours at sub-daily time scales (in the case of Los Angeles) are key factors not captured by the same-day accumulations. Accordingly, we suggest that the assessment of future changes in landslide hazard for the entire the West Coast requires consideration of future changes in the occurrence and intensity of atmospheric rivers, in their duration and clustering, and in the occurrence of short-duration (sub-daily) extreme rainfall as well. Major regional landslide events, in which multiple occurrences are recorded in the catalog for the same day, are too rare to allow a statistical characterization of their triggering events, but a case study analysis indicates that a variety of synoptic-scale events can be involved, including not only atmospheric rivers but also broader cold- and warm-front precipitation. That a news-based catalog of landslides is accurate enough to allow the identification of different landslide/rainfall relationships in the major urban areas along the US West Coast suggests that this technology can potentially be used for other English-language cities and could become an even more powerful tool if expanded to other languages and non-traditional news sources, such as social media.

Modeling streamflow and sediment using SWAT in Ethiopian Highlands

The coincidence of intensive rainfall events at the beginning of the rainy season and unprotected soil conditions after extreme dry spells expose the Ethiopian Highlands to severe soil erosion. Soil and water conservation measures (SWC) have been applied to counteract land degradation in the endangered areas, but SWC efficiency may vary related to the heterogeneity of the landscape. The Soil and Water Assessment Tool (SWAT) model was used to model hydrology and sediment dynamics of a 53.7 km2 watershed, located in the Lake Tana basin, Ethiopia. Spatially distributed stone bund impacts were applied in the model through modification of the surface runoff ratio and adjustment of a support practice factor simulating the trapped amounts of water and sediment at the SWC structure and watershed level. The resulting Nash-Sutcliffe efficiency (NSE) for daily streamflow simulation was 0.56 for the calibration and 0.48 for the validation period, suggesting satisfactory model performance. In contrast, the daily sediment simulation resulted in unsatisfactory model performance, with the NSE value of 0.07 for the calibration and –1.76 for the validation period and this could be as a result of high intensity and short duration rainfall events in the watershed. Meanwhile, insufficient sediment yield prediction may result to some extent from daily based data processing, whereas the driving runoff events and thus sediment loads occur on sub-daily time scales, probably linked with abrupt gully breaks and development. The calibrated model indicated 21.08 Mg/hm2 average annual sediment yield, which is far beyond potential soil regeneration rate. Despite the given limits of model calibration, SWAT may support the scaling up and out of experimentally proven SWC interventions to encourage sustainable agriculture in the Ethiopian Highlands. Keywords: SWAT, streamflow, sediment dynamics, soil erosion, soil and water conservation, watershed hydrology DOI: 10.3965/j.ijabe.20160905.2483 Citation: Addis H K, Strohmeier S, Ziadat F, Melaku N D, Klik A. Modeling streamflow and sediment using SWAT in the Ethiopian Highlands. Int J Agric & Biol Eng, 2016; 9(5): 51－66.

Modeling streamflow and sediment using SWAT in Ethiopian Highlands

The coincidence of intensive rainfall events at the beginning of the rainy season and unprotected soil conditions after extreme dry spells expose the Ethiopian Highlands to severe soil erosion. Soil and water conservation measures (SWC) have been applied to counteract land degradation in the endangered areas, but SWC efficiency may vary related to the heterogeneity of the landscape. The Soil and Water Assessment Tool (SWAT) model was used to model hydrology and sediment dynamics of a 53.7 km2 watershed, located in the Lake Tana basin, Ethiopia. Spatially distributed stone bund impacts were applied in the model through modification of the surface runoff ratio and adjustment of a support practice factor simulating the trapped amounts of water and sediment at the SWC structure and watershed level. The resulting Nash-Sutcliffe efficiency (NSE) for daily streamflow simulation was 0.56 for the calibration and 0.48 for the validation period, suggesting satisfactory model performance. In contrast, the daily sediment simulation resulted in unsatisfactory model performance, with the NSE value of 0.07 for the calibration and –1.76 for the validation period and this could be as a result of high intensity and short duration rainfall events in the watershed. Meanwhile, insufficient sediment yield prediction may result to some extent from daily based data processing, whereas the driving runoff events and thus sediment loads occur on sub-daily time scales, probably linked with abrupt gully breaks and development. The calibrated model indicated 21.08 Mg/hm2 average annual sediment yield, which is far beyond potential soil regeneration rate. Despite the given limits of model calibration, SWAT may support the scaling up and out of experimentally proven SWC interventions to encourage sustainable agriculture in the Ethiopian Highlands. Keywords: SWAT, streamflow, sediment dynamics, soil erosion, soil and water conservation, watershed hydrology DOI: 10.3965/j.ijabe.20160905.2483 Citation: Addis H K, Strohmeier S, Ziadat F, Melaku N D, Klik A. Modeling streamflow and sediment using SWAT in the Ethiopian Highlands. Int J Agric & Biol Eng, 2016; 9(5): 51－66.

The Time Scales of Variability of Marine Low Clouds

AbstractMultidecade global regressions of inversion strength, vertical velocity, and sea surface temperature (SST) on low cloud amount, from subdaily to multiyear time scales, refute the dominance of seasonal inversion strength on marine low cloud variability. Multiday low cloud variance averaged over the eastern Pacific and Atlantic stratocumulus regions [5 × 10−2 (cloud amount)2] is twice the subdaily variance and 5 times larger than the multimonth variance. The broad multiday band contains most (60%) of the variance, despite strong seasonal (annual) and diurnal spectral peaks. Multiday low cloud amount over the eastern tropical and midlatitude oceans is positively correlated to inversion strength, with a slope of 2%–5% K−1. Anecdotes show multiday low cloud and inversion strength anomalies propagate equatorward from midlatitudes. Previously shown correlations of low clouds to strong inversions and cool SST on monthly and longer time scales in the stratocumulus regions imply positive cloud-radiative feedbacks, with e-folding time scales of 300 days for SST and 14 days for atmospheric boundary layer temperature. On multimonth time scales, removing the effect of SST on low clouds reduces the low cloud amount explained by inversion strength by a factor of 3, but SST has a small effect at other time scales. Contrary to their positive correlation in the stratocumulus cloud decks, low clouds are anticorrelated to inversion strength over most of the tropics on daily and subdaily time scales.

Trend Analysis for Extreme Rainfall at Sub-Daily and Daily Timescales in Côte d’Ivoire

Extreme rainfall events are meteorological hazards that cause great damage and many casualties in the world. This paper examines the trends in extreme rainfall from 10 sub-daily time series and 44 daily time series in Côte d’Ivoire. Rainfall data were converted into indices. In total, six (6) indices were used for daily extreme rainfall and one (1) index for sub-daily extreme rainfall (15 to 240 min). Two statistical tests for trend detection were used to evaluate the possible trend in these precipitation data. The first is a Mann-Kendall non-parametric trend test, used to evaluate the existence of monotonic trends. The second is a linear regression method, based on a parametric approach to trend detection. Results show that very few statistically significant decreasing trends can be detected at the sub-daily and daily timescales. Some decreasing trends in extreme rainfall events were localized in the south and southeast. These results could enhance the implementation of adaptation systems to flood risk.

Spatial and Temporal Characteristics of Summer Precipitation over Central Europe in a Suite of High-Resolution Climate Models

AbstractHigh-impact, locally intense rainfall episodes represent a major socioeconomic problem for societies worldwide, and at the same time these events are notoriously difficult to simulate properly in climate models. Here, the authors investigate how horizontal resolution and model formulation influence this issue by applying the HIRLAM–ALADIN Regional Mesoscale Operational NWP in Europe (HARMONIE) Climate (HCLIM) regional model with three different setups: two using convection parameterization at 15- and 6.25-km horizontal resolution (the latter within the “gray zone” scale), with lateral boundary conditions provided by ERA-Interim and integrated over a pan-European domain, and one with explicit convection at 2-km resolution (HCLIM2) over the Alpine region driven by the 15-km model. Seven summer seasons were sampled and validated against two high-resolution observational datasets. All HCLIM versions underestimate the number of dry days and hours by 20%–40% and overestimate precipitation over the Alpine ridge. Also, only modest added value was found for gray-zone resolution. However, the single most important outcome is the substantial added value in HCLIM2 compared to the coarser model versions at subdaily time scales. It better captures the local-to-regional spatial patterns of precipitation reflecting a more realistic representation of the local and mesoscale dynamics. Further, the duration and spatial frequency of precipitation events, as well as extremes, are closer to observations. These characteristics are key ingredients in heavy rainfall events and associated flash floods, and the outstanding results using HCLIM in a convection-permitting setting are convincing and encourage further use of the model to study changes in such events in changing climates.

Contribution of large-scale circulation anomalies to changes in extreme precipitation frequency in the United States

The mean global climate has warmed as a result of the increasing emission of greenhouse gases induced by human activities. This warming is considered the main reason for the increasing number of extreme precipitation events in the US. While much attention has been given to extreme precipitation events occurring over several days, which are usually responsible for severe flooding over a large region, little is known about how extreme precipitation events that cause flash flooding and occur at sub-daily time scales have changed over time. Here we use the observed hourly precipitation from the North American Land Data Assimilation System Phase 2 forcing datasets to determine trends in the frequency of extreme precipitation events of short (1 h, 3 h, 6 h, 12 h and 24 h) duration for the period 1979–2013. The results indicate an increasing trend in the central and eastern US. Over most of the western US, especially the Southwest and the Intermountain West, the trends are generally negative. These trends can be largely explained by the interdecadal variability of the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation (AMO), with the AMO making a greater contribution to the trends in both warm and cold seasons.

Spatiotemporal Evaluation of the Gauge-Adjusted Global Satellite Mapping of Precipitation at the Basin Scale

This study evaluated the accuracy of gauge-adjusted Global Satellite Mapping of Precipitation (GSMaP_Gauge version V5.222.1, hereafter G_Gauge) data in Japan’s Tone River basin during 2006-2009. Specifically, the accuracy of a gauge non-adjusted product, GSMaP Moving Vector with Kalman Filter (GSMaP_MVK, hereafter G_MVK), was also evaluated. Both products were also evaluated against ground observation data from rain gauge-radar combined product Radar-Automated Meteorological Data Acquisition System (Radar-AMeDAS) in terms of temporal and spatial variability. Temporal analyses showed that G_Gauge had better accuracy than G_MVK at sub-daily time scales (1, 3, 6, 9, 12, and 24 h) within any range of precipitation intensity and better detection capabilities of rainfall event. Linear regressions with Radar-AMeDAS showed better performance for G_Gauge than G_MVK at any time scales in terms of Pearson’s correlation coefficient and the slope of regression. At an hourly scale, in particular, Pearson’s correlation coefficient for G_Gauge (0.84) was higher than that for G_MVK (0.72) as well as the slope of linear regression (0.87 and 0.65, respectively). The probability of detection (POD) improved from 0.48 (G_MVK) to 0.70 (G_Gauge) when gauge-adjusted data were used. However, spatial analysis detected that G_Gauge still underestimated the precipitation intensity in high-elevation regions and slightly overestimated it in low elevation regions. The POD and false alarm ratio had a linear relationship with log-transformed elevation data, and the relationships were stronger in the winter seasons than in the summer seasons. At any spatial and temporal scale, the evaluation of these products should consider seasonal changes (especially in winter) and the topographic effects. For further improvements of G_Gauge, we suggest including higher resolution gauge-based network data than the Climate Prediction Center unified gauge-based analysis of global daily precipitation, which is used for G_Gauge.

Remote Sensing of Terrestrial Rainfall From Ku-Band Scatterometers

Rainfall is the most fundamental variable of the terrestrial hydrological cycle. However, in many regions of the world, ground observations are still very scarce or even missing. Recently, a bottom-up approach, named SM2RAIN, for terrestrial rainfall estimation from satellite soil moisture (SM) products was proposed and successfully applied to C- and L-band products from scatterometers and radiometers. Thanks to the multiple Ku-band scatterometers launched in the recent years and a number of new sensors expected in the near future, accurate rainfall estimation at subdaily time scale could be obtained. We present here a first attempt to estimate terrestrial rainfall from Ku-band scatterometers using SM2RAIN. To this end, backscattering data (sigma-0) collected in central Italy from the RapidScat instrument on board the International Space Station are compared with the Advanced SCATterometer (ASCAT, C-band) SM product and in situ observations for assessing its sensitivity to SM variations. Then, RapidScat sigma-0 is used for rainfall retrieval and compared with ground observations over a regular grid of 15-km spacing. The 8-month period from Nov 2014 to Jun 2015 is considered. Results show a very good agreement between ASCAT SM and RapidScat SM index with a median temporal correlation coefficient R of ${\sim}{0}.{9}$ and a reasonable performance ( $R > {0}.{52}$ ) against in situ data. More interestingly, the performance of RapidScat in 1-day rainfall estimation is found to be satisfactory with median R -values equal to ${\sim}{0}.{6}$ . These promising results highlight the large potential of using the constellation of scatterometers for providing an accurate rainfall product with high spatial-temporal resolution.

Evaluation of GPM Day-1 IMERG and TMPA Version-7 legacy products over Mainland China at multiple spatiotemporal scales

Summary The post-real time product of Day-1 Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) is evaluated over Mainland China from April to December 2014 at the hourly timescale, against data from hourly ground-based observations. In addition, the IMERG product is compared with its predecessor-the Version-7 post-real-time 3B42 (3B42V7) product of Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) at its original 3-hourly and then daily timescales for the same period. All the products are cross-evaluated at gridded, regional, and national scales. Results show that: (1) the Day-1 IMERG shows appreciably better performance than 3B42V7 at both sub-daily and daily timescales, and all the three spatial scales. The gap between the two products is more significant at the sub-daily resolution; (2) Out of the six sub-regions of China, IMERG especially performs better than 3B42V7 at the mid- and high-latitudes, as well as relatively dry climate regions; (3) IMERG can better reproduce the probability density function (PDF) in terms of precipitation intensity, particularly in the low ranges; and (4) although IMERG better captures the precipitation diurnal variability, both products have room to further improve their capability, particularly in the dry climate and high-latitude regions. This study is among the earliest evaluation and comparison of IMERG and 3B42V7 products, which could be valuable in providing reference for the development of IMERG algorithms, associated global products, and various applications as well.

A simple procedure for the assessment of hydropeaking flow alterations applied to several European streams

Release of water from storage hydropower plants generates rapid flow and stage fluctuations (hydropeaking) in the receiving water bodies at a variety of sub-daily time-scales. In this paper we present an approach to quantify such variations, which is easy to apply, requires stream flow data at a readily available resolution, and allows for the comparison of hydropeaking flow alteration amongst several gauged stations. Hydropeaking flow alteration is quantified by adopting a rigorous statistical approach and using two indicators related to flow magnitude and rate of change. We utilised a comprehensive stream-flow dataset of 105 gauging stations from Italy, Switzerland and Norway to develop our method. Firstly, we used a GIS approach to objectively assign the stations to one of two groups: gauges with an upstream water release from hydropower plants (peaked group) and without upstream releases (unpeaked group). Secondly, we used the datasets of the unpeaked group to calculate one threshold for each of the two indicators. Thresholds defined three different classes: absent or low pressure, medium, and high pressure, and all stations were classified according to these pressure levels. Thirdly, we showed that the thresholds can change, depending on the country dataset, the year chosen for the analysis, the number of gauging stations, and the temporal resolution of the dataset, but the outcome of the classification remains the same. Hence, the classification method we propose can be considered very robust since it is almost insensitive to the hydropeaking thresholds variability. Therefore, the method is broadly applicable to procedures for the evaluation of flow regime alterations and classification of river hydromorphological quality, and may help to guide river restoration actions.

Projected Changes in Intense Precipitation over Europe at the Daily and Subdaily Time Scales*

Abstract Heavy precipitation is a major hazard over Europe. It is well established that climate model projections indicate a tendency toward more extreme daily rainfall events. It is still uncertain, however, how this changing intensity translates at the subdaily time scales. The main goal of the present study is to examine possible differences in projected changes in intense precipitation events over Europe at the daily and subdaily (3-hourly) time scales using a state-of-the-science climate model. The focus will be on one representative concentration pathway (RCP8.5), considered as illustrative of a high rate of increase in greenhouse gas concentrations over this century. There are statistically significant differences in intense precipitation projections (up to 40%) when comparing the results at the daily and subdaily time scales. Over northeastern Europe, projected precipitation intensification at the 3-hourly scale is lower than at the daily scale. On the other hand, Spain and the western seaboard exhibit an opposite behavior, with stronger intensification at the 3-hourly scale rather than the daily scale. While the mean properties of the precipitation distributions are independent of the analyzed frequency, projected precipitation intensification exhibits regional differences. This finding has implications for the extrapolation of impacts of intense precipitation events, given the daily time scale at which the analyses are usually performed.

Modeling watershed-scale solute transport using an integrated, process-based hydrologic model with applications to bacterial fate and transport

Summary Distributed hydrologic models that simulate fate and transport processes at sub-daily timescales are useful tools for estimating pollutant loads exported from watersheds to lakes and oceans downstream. There has been considerable interest in the application of integrated process-based hydrologic models in recent years. While the models have been applied to address questions of water quantity and to better understand linkages between hydrology and land surface processes, routine applications of these models to address water quality issues are currently limited. In this paper, we first describe a general process-based watershed-scale solute transport modeling framework, based on an operator splitting strategy and a Lagrangian particle transport method combined with dispersion and reactions. The transport and the hydrologic modules are tightly coupled and the interactions among different hydrologic components are explicitly modeled. We test transport modules using data from plot-scale experiments and available analytical solutions for different hydrologic domains. The numerical solutions are also compared with an analytical solution for groundwater transit times with interactions between surface and subsurface flows. Finally, we demonstrate the application of the model to simulate bacterial fate and transport in the Red Cedar River watershed in Michigan and test hypotheses about sources and transport pathways. The watershed bacterial fate and transport model is expected to be useful for making near real-time predictions at marine and freshwater beaches.