Profile inference revisited

Profile-guided optimization (PGO) is an important component in modern compilers. By allowing the compiler to leverage the program’s dynamic behavior, it can often generate substantially faster binaries. Sampling-based profiling is the state-of-the-art technique for collecting execution profiles in data-center environments. However, the lowered profile accuracy caused by sampling fully optimized binary often hurts the benefits of PGO; thus, an important problem is to overcome the inaccuracy in a profile after it is collected. In this paper we tackle the problem, which is also known as profile inference and profile rectification . We investigate the classical approach for profile inference, based on computing minimum-cost maximum flows in a control-flow graph, and develop an extended model capturing the desired properties of real-world profiles. Next we provide a solid theoretical foundation of the corresponding optimization problem by studying its algorithmic aspects. We then describe a new efficient algorithm for the problem along with its implementation in an open-source compiler. An extensive evaluation of the algorithm and existing profile inference techniques on a variety of applications, including Facebook production workloads and SPEC CPU benchmarks, indicates that the new method outperforms its competitors by significantly improving the accuracy of profile data and the performance of generated binaries.

Impacts of Climate Change and Variability on Precipitation and Maximum Flows in Devil’s Creek, Tacna, Peru

Global projections of climate change indicate negative impacts on hydrological systems, with significant changes in precipitation and temperature in many parts of the world. As a result, floods and droughts are expected. This article discusses the potential effects of climate change and variability on the maximum precipitation, temperature, and hydrological regime in Devil’s Creek, Tacna, Peru. The outputs of precipitation and daily temperature of fifteen regional climate models were used for the RCP4.5 and RCP8.5 emission scenarios. The methodology used includes the bias correction and downscaling of meteorological variables using the quintiles mapping technique, hydrological modeling, the evaluation of two emission scenarios, and its effect on the maximum flows of the stream. The results of the multi-model ensemble show that the maximum annual precipitation will probably increase by more than 30% for the RCP4.5 and RCP8.5 scenarios for the 2021–2050 period relative to the 1981–2005 period. Likewise, as expected, the maximum flows could increase by 220% and 154% for the RCP4.5 scenarios for the 2021–2050 and 2051–2080 terms, respectively, and 234% and 484% for the RCP8.5 scenarios and for the 2021–2050 and 2051–2080 terms, respectively, concerning the recorded historical value, increasing the probability of flood events and damage in populations located downstream.

Lexicographically Maximum Flows under an Arc Interdiction

Network interdiction problem arises when an unwanted agent attacks the network system to deteriorate its transshipment efficiency. Literature is flourished with models and solution approaches for the problem. This paper considers a single commodity lexicographic maximum flow problem on a directed network with capacitated vertices to study two network flow problems under an arc interdiction. In the first, the objective is to find an arc on input network to be destroyed so that the residual lexicographically maximum flow is lexicographically minimum. The second problem aims to find a flow pattern resulting lexicographically maximum flow on the input network so that the total residual flow, if an arc is destroyed, is maximum. The paper proposes strongly polynomial time solution procedures for these problems.

Climate Change Impact on the Magnitude and Timing of Hydrological Extremes Across Great Britain

Climate change could intensify hydrological extremes, changing not just the magnitude but also the timing of flood and drought events. Understanding these potential future changes to hydrological extremes at the national level is critical to guide policy decisions and ensure adequate adaptation measures are put in place. Here, climate change impact on the magnitude and timing of extreme flows is modelled across Great Britain (GB), using an ensemble of climate data from the latest UK Climate Projections product (UKCP18) and a national grid-based hydrological model. All ensemble members show large reductions in low flows, of around −90 to −25% for 10-year return period low flows by 2050–2080. The direction of change for high flows is uncertain, but increases in 10-year return period high flows of over 9% are possible across most of the country. Simultaneous worsening of both extremes (i.e., a reduction in low flows combined with an increase in high flows) are projected in the west. Changes to flow timing are also projected; with mostly earlier annual maximum flows across Scotland, later annual maximum flows across England and Wales, and later low flows across GB. However, these changes are generally not statistically significant due to the high interannual variability of annual maximum/minimum flow timing. These results highlight the need for adaptation strategies that can cope with a wide range of future changes in hydrological extremes, and consider changes in the timing as well as magnitude.

Avaliação de metodologias de transferência de vazões de referência em bacias hidrográficas: sua aplicação na bacia do rio Japaratuba - Sergipe - Brasil

Para avaliar a disponibilidade de água e definir as áreas de inundação nas bacias hidrográficas, é necessário considerar a vazão mínima, média e máxima, denominadas de vazões de referência, e isto requer dados observados de vazão, que são bem escassos em bacias brasileiras, principalmente as pequenas e médias bacias. Para superar esta falta, utiliza-se dados de bacias contribuintes com comportamento hidrológico similar, que são transferidos por meio de operações matemáticas, utilizando variáveis físicas e climáticas. Tais procedimentos, geralmente, são mal avaliados quanto à sua precisão. Assim, objetivou avaliar a acurácia da estimação de cinco vazões de referência em quatro estações de medição dos dois principais afluentes do rio Japaratuba (Sergipe, Brasil), os rios Japaratuba-Mirim e Siriri. Os resultados mostraram diferentes comportamentos para as duas sub-bacia, quer seja pelas variáveis influentes, quer seja pelos efeitos antrópicos como a mudança no uso do solo que precisam ser melhor avaliados. Para a bacia do rio Japaratuba-Mirim a transferência de vazões mínimas e médias deve ser realizada considerando-se o produto área x precipitação média anual e para as vazões máximas deve-se considerar o comprimento do rio até a seção. Para a bacia do Siriri, os melhores resultados de transferência de vazões médias e máximas foram obtidos com o produto "área x precipitação média anual” e a variável "precipitação média anual" gerou um erro menor para as vazões mínimas. Assessing the reference flow transfer methodologies in watersheds: their application at Japaratuba River Basin – Sergipe State – BrazilA B S T R A C TIn order to evaluate the water availability and define the flood areas in the river basins, it is necessary to consider minimum, medium and maximum discharge, called reference flows requiring records on flow data, quite scarce in Brazilian river basin, mainly those of small and medium scale. To overcome this gap, data from nearby basins with similar hydrological behavior are used, based on mathematical operations involving physical and climatic variables of the contributing basins. However, these procedures are poorly evaluated for their accuracy. Thus, this study aimed to evaluate the accuracy of the estimation of five reference flows through the transfer of information, using physical and climatic variables in four gage stations of the main tributaries of the Japaratuba river basin (Japaratuba-Mirim and Siriri river) - Sergipe State, Brazil. The results showed different behaviors for the two sub-basins as for either by influential variables or by anthropic effects such as land use and land cover changes that need to be better evaluated. The flow transfer to the subbasin of the Japaratuba-Mirim river should be performed considering the product "Area x Mean annual rainfall" for minimum and medium flows. For maximum flows the "Length" of the basin should be considered. For the Siriri river basin, the "Mean annual rainfall" variable generated a smaller error in the minimum flows and the product "Area x Mean annual rainfall” led to better results for medium and maximum flows.Keywords: Water resource management; statistical hydrology; geographic information systems.

Future changes in annual, seasonal and monthly runoff signatures in contrasting Alpine catchments in Austria

Hydrological regimes of alpine catchments are expected to be strongly affected by climate change, mostly due to their dependence on snow and ice dynamics. While seasonal changes have been studied extensively, studies on changes in the timing and magnitude of annual extremes remain rare. This study investigates the effects of climate change on runoff patterns in six contrasting Alpine catchments in Austria using a process-based, semi-distributed hydrological model and projections from 14 regional and global climate model combinations for two representative concentration pathways, namely RCP4.5 and RCP8.5. The study catchments represent a spectrum of different hydrological regimes, from pluvial–nival to nivo-glacial, as well as distinct topographies and land forms, characterizing different elevation zones across the eastern Alps to provide a comprehensive picture of future runoff changes. The climate projections are used to model river runoff in 2071–2100, which are then compared to the 1981–2010 reference period for all study catchments. Changes in the timing and magnitude of annual maximum and minimum flows, as well as in monthly runoff and snowmelt, are quantified and analyzed. Our results indicate a substantial shift to earlier occurrences in annual maximum flows by 9 to 31 d and an extension of the potential flood season by 1 to 3 months for high-elevation catchments. For low-elevation catchments, changes in the timing of annual maximum flows are less pronounced. Magnitudes of annual maximum flows are likely to increase by 2 %–18 % under RCP4.5, while no clear changes are projected for four catchments under RCP8.5. The latter is caused by a pronounced increase in evaporation and decrease in snowmelt contributions, which offset increases in precipitation. In the future, minimum annual runoff will occur 13–31 d earlier in the winter months for high-elevation catchments, whereas for low-elevation catchments a shift from winter to autumn by about 15–100 d is projected, with generally larger changes for RCP8.5. While all catchments show an increase in mean magnitude of minimum flows by 7–30% under RCP4.5, this is only the case for four catchments under RCP8.5. Our results suggest a relationship between the elevation of catchments and changes in the timing of annual maximum and minimum flows. For the magnitude of the extreme flows, a relationship is found between catchment elevation and annual minimum flows, whereas this relationship is lacking between elevation and annual maximum flow.

Recent Changes in Hydroclimatic Patterns over Medium Niger River Basins at the Origin of the 2020 Flood in Niamey (Niger)

Niamey, the capital of Niger, is particularly prone to floods, since it is on the banks of the Niger River, which in its middle basin has two flood peaks: one in summer (the red flood) and one in winter (the black flood). In 2020, the Niger River in Niamey reached its all-time highest levels following an abundant rainy season. On the other hand, the floods in Niamey have been particularly frequent in the last decade, a symptom of a change in hydroclimatic behaviour already observed since the end of the great droughts of the 1970s and 1980s and which is identified with the name of Sahelian Paradox. This study, starting from the analysis of the 2020 flood and from the update of the rating curve of the Niamey hydrometric station, analyses the rainfall–runoff relationship on the Sahelian basins of the Medium Niger River Basin (MNRB) that are at the origin of the local flood. The comparative analysis of runoffs, annual maximum flows (AMAX) and runoff coefficients with various rainfall indices calculated on gridded datasets allowed to hydroclimatically characterise the last decade as a different period from the wet one before the drought, the dry one and the post-drought one. Compared to the last one, the current period is characterised by a sustained increase in hydrological indicators (AMAX +27%) consistent with the increase in both the accumulation of precipitation (+11%) and the number (+51%) and magnitude (+54%) of extreme events in the MNRB. Furthermore, a greater concentration of rainfall and extremes (+78%) in August contributes to reinforcing the red flood’s positive anomalies (+2.23 st.dev in 2020). The study indicates that under these conditions the frequency of extreme hydrological events in Niamey will tend to increase further also because of the concurrence of drivers such as river-bed silting and levee effects. Consequently, the study concludes with the need for a comprehensive flood-risk assessment on the Niamey city that considers both recent hydroclimatic trends and urbanisation dynamics in flood zones hence defining the most appropriate risk-reduction strategies.

Assessing Climatic Drivers of Spring Mean and Annual Maximum Flows in Western Canadian River Basins

Flows originating from cold and mountainous watersheds are highly dependent on temperature and precipitation patterns, and the resulting snow accumulation and melt conditions, affecting the magnitude and timing of annual peak flows. This study applied a multiple linear regression (MLR) modelling framework to investigate spatial variations and relative importance of hydroclimatic drivers of annual maximum flows (AMF) and mean spring flows (MAMJflow) in 25 river basins across western Canada. The results show that basin average maximum snow water equivalent (SWEmax), April 1st SWE and spring precipitation (MAMJprc) are the most important predictors of both AMF and MAMJflow, with the proportion of explained variance averaging 51.7%, 44.0% and 33.5%, respectively. The MLR models’ abilities to project future changes in AMF and MAMJflow in response to changes to the hydroclimatic controls are also examined using the Canadian Regional Climate Model (CanRCM4) output for RCP 4.5 and RCP8.5 scenarios. The results show considerable spatial variations depending on individual watershed characteristics with projected changes in AMF ranging from −69% to +126% and those of MAMJflow ranging from −48% to +81% by the end of this century. In general, the study demonstrates that the MLR framework is a useful approach for assessing the spatial variation in hydroclimatic controls of annual maximum and mean spring flows in the western Canadian river basins. However, there is a need to exercise caution in applying MLR models for projecting changes in future flows, especially for regulated basins.

Influência do uso e ocupação do solo na disponibilidade hídrica das bacias dos rios Peruípe, Itanhém e Jucuruçu, Bahia

O processo de modificação da paisagem através da retirada da vegetação nativa para a implantação de atividade antrópicas acarreta alterações no comportamento hidrológico de uma bacia hidrográfica. Diante disso, este trabalho teve como objetivo analisar a influência da alteração do uso e ocupação do solo na disponibilidade hídrica das bacias hidrográficas dos rios Peruípe, Itanhém e Jucuruçu, no período de 1990 a 2018. Para tanto, utilizou-se dados das séries históricas das estações fluviométricas localizadas nas áreas de drenagem das bacias, importadas do portal HidroWeb da Agência Nacional de Águas e Saneamento Básico (ANA). A partir destas, foram obtidas as variáveis hidrológicas anuais: vazão máxima, vazão média e mínima. Já os dados de uso e ocupação do solo foram cedidos pelo Fórum Florestal do Extremo Sul da Bahia e estes passaram por processamento no software QGIS, onde foram obtidas as áreas de cada classe de uso e ocupação do solo. Posteriormente, fez-se a associação dos dados através de análise quantitativa executada no software SAS, onde foram obtidas as correlações simples entre as variáveis. As formas de uso do solo nas bacias hidrográficas estudadas passaram por significativa redução das áreas de vegetação nativa em virtude do crescimento das áreas de atividades antrópicas, principalmente as destinadas a pecuária e silvicultura. A análise de correlação demonstrou que a expansão dessas áreas tem influenciado a diminuição das vazões mínimas. Em contrapartida, apesar da diminuição significativa das áreas de vegetação nativa, os remanescentes florestais continuam atuando na redução das vazões máximas e aumento das vazões mínimas. Influence of land use and occupation on water availability in the Peruípe, Itanhém and Jucuruçu river basins, BahiaABSTRACTThe process of modifying the landscape through the removal of native vegetation for the implementation of anthropic activities causes changes in the hydrological behavior of a hydrographic basin. In view of this, this study aimed to analyze the influence of changes in land use and occupation on the water availability of the hydrographic basins of the Peruípe, Itanhém and Jucuruçu rivers, from 1990 to 2018. For this purpose, data from the historical series were used. the fluviometric stations belonging to the drainage areas of the basins, imported from the HidroWeb portal of the National Water Agency. From these, the hydrological variables were obtained: maximum flow, average and minimum flow. The data on land use and occupation were provided by the Forest Forum of the Extreme South of Bahia and these were processed in the QGIS software, where the areas of each class of land use and occupation were obtained. Subsequently, the association of the data was made through quantitative analysis performed in the software SAS University Edition, where simple correlations between variables were obtained. The forms of land use and occupation in the hydrographic basins studied underwent a significant reduction in the areas of native vegetation due to the growth of the areas of anthropic activities, mainly those destined for livestock and forestry. The correlation analysis showed that the expansion of these areas has influenced the decrease in minimum flows. On the other hand, despite the significant decrease in the areas of native vegetation, the forest remnants continue to act in reducing maximum flows and increasing minimum flows. Influence of land use and occupation on water availability in the Peruípe, Itanhém and Jucuruçu river basins, Bahia A B S T R A C TThe process of modifying the landscape through the removal of native vegetation for the implementation of anthropic activities causes changes in the hydrological behavior of a hydrographic basin. In view of this, this study aimed to analyze the influence of changes in land use and occupation on the water availability of the hydrographic basins of the Peruípe, Itanhém and Jucuruçu rivers, from 1990 to 2018. For this purpose, data from the historical series were used. the fluviometric stations belonging to the drainage areas of the basins, imported from the HidroWeb portal of the National Water Agency. From these, the hydrological variables were obtained: maximum flow, average and minimum flow. The data on land use and occupation were provided by the Forest Forum of the Extreme South of Bahia and these were processed in the QGIS software, where the areas of each class of land use and occupation were obtained. Subsequently, the association of the data was made through quantitative analysis performed in the software SAS University Edition, where simple correlations between variables were obtained. The forms of land use and occupation in the hydrographic basins studied underwent a significant reduction in the areas of native vegetation due to the growth of the areas of anthropic activities, mainly those destined for livestock and forestry. The correlation analysis showed that the expansion of these areas has influenced the decrease in minimum flows. On the other hand, despite the significant decrease in the areas of native vegetation, the forest remnants continue to act in reducing maximum flows and increasing minimum flows.Keywords: geoprocessing, hydrological behavior, water inertia.

Timing and magnitude of runoff in Austrian mountain catchments in a warming climate

<p>Hydrological regimes of alpine catchments are expected to be strongly influenced by climate change due to their dependence on snow dynamics. While seasonal changes have been studied extensively, studies on changes in the timing and magnitude of annual extremes remain rare. This study investigates the effects of climate change on runoff patterns in six alpine catchments in Austria by using a topography-driven semi-distributed hydrological model and 14 climate projections for RCP 4.5 and RCP 8.5. The study catchments represent a range of alpine catchments, from pluvial-nival to nivo-glacial, as the study focuses on providing a comprehensive picture of future runoff changes on catchments at different altitudes. Simulations of 1981-2010 are compared to projections of 2071-2100 by examining changes in timing and magnitude of annual maximum and minimum flows as well as monthly discharges.</p><p>Our results indicate a substantial shift to earlier occurrences in annual maximum flows by 9 to 31 days on average and an extension of the potential flood season by 1 to 3 months for high elevation catchments. For lower elevation catchments, changes in timing of annual maximum flows are less pronounced. Magnitudes of annual maximum flows are likely to increase, with four catchments exhibiting larger increases under RCP 4.5 compared to RCP 8.5. The timing of minimum annual discharges shifts to earlier in the winter months for high elevation catchments, whereas for lower elevation catchments a shift from winter to autumn is observed. While all catchments show an increase in mean magnitude of minimum flows under RCP 4.5, this is not the case for two low elevation catchments under RCP 8.5.</p><p>Our results suggest a relationship between the altitude of catchments and changes in timing of annual maximum and minimum flows and magnitude of low flows, whereas no relationship between altitude and magnitude of annual maximum flows could be distinguished.</p>