On the nature of rainfall intermittency as revealed by different metrics and sampling approaches

A general consensus on the concept of rainfall intermittency has not yet been reached, and intermittency is often attributed to different aspects of rainfall variability, including the fragmentation of the rainfall support (i.e., the alternation of wet and dry intervals) and the strength of intensity fluctuations and bursts. To explore these different aspects, a systematic analysis of rainfall intermittency properties in the time domain is presented using high-resolution (1-min) data recorded by a network of 201 tipping-bucket gauges covering the entire island of Sardinia (Italy). Four techniques, including spectral and scale invariance analysis, and computation of clustering and intermittency exponents, are applied to quantify the contribution of the alternation of dry and wet intervals (i.e., the rainfall support fragmentation), and the fluctuations of intensity amplitudes, to the overall intermittency of the rainfall process. The presence of three ranges of scaling regimes between 1 min to ~ 45 days is first demonstrated. In accordance with past studies, these regimes can be associated with a range dominated by single storms, a regime typical of frontal systems, and a transition zone. The positions of the breaking points separating these regimes change with the applied technique, suggesting that different tools explain different aspects of rainfall variability. Results indicate that the intermittency properties of rainfall support are fairly similar across the island, while metrics related to rainfall intensity fluctuations are characterized by significant spatial variability, implying that the local climate has a significant effect on the amplitude of rainfall fluctuations and minimal influence on the process of rainfall occurrence. In addition, for each analysis tool, evidence is shown of spatial patterns of the scaling exponents computed in the range of frontal systems. These patterns resemble the main pluviometric regimes observed on the island and, thus, can be associated with the corresponding synoptic circulation patterns. Last but not least, we demonstrate how the methodology adopted to sample the rainfall signal from the records of the tipping instants can significantly affect the intermittency analysis, especially at smaller scales. The multifractal scale invariance analysis is the only tool that is insensitive to the sampling approach. Results of this work may be useful to improve the calibration of stochastic algorithms used to downscale coarse rainfall predictions of climate and weather forecasting models, as well as the parameterization of intensity-duration-frequency curves, adopted for land planning and design of civil infrastructures

Physical controls on the scale-dependence of ensemble streamflow forecast dispersion

Abstract. The accuracy of ensemble streamflow forecasts (ESFs) is impacted by the propagation of uncertainty associated with quantitative precipitation forecasts (QPFs) through the physical processes occurring in the basin. In this study, we consider consistent ESFs (i.e., observations and ensemble members are equally likely) and we study the effect of basin area (A) and antecedent rainfall (AR) on the ESF dispersion, a metric of flood forecast skill. Results from a set of numerical experiments indicate that: (i) for small basins (≲180 km2), ESF dispersion is mainly dominated by the runoff generation process and does not depend on the basin size A; (ii) for larger areas, ESF dispersion decreases with A according to a log-linear relation due to the decreasing variability of ensemble QPFs and, possibly, to the channel routing process. In addition, we found that, regardless the basin size, the ESF dispersion decreases as AR increases, and that the influence of AR is larger for basins with fast response times. Physical controls (land cover, soil texture and morphometric features) on the analyzed basin response confirm these interpretations

Distributed hydrologic modeling of a sparsely monitored basin in Sardinia, Italy, through hydrometeorological downscaling

The water resources and hydrologic extremes in Mediterranean basins are heavily influenced by climate variability. Modeling these watersheds is difficult due to the complex nature of the hydrologic response as well as the sparseness of hydrometeorological observations. In this work, we present a strategy to calibrate a distributed hydrologic model, known as TIN-based Real-time Integrated Basin Simulator (tRIBS), in the Rio Mannu basin (RMB), a medium-sized watershed (472.5 km2) located in an agricultural area in Sardinia, Italy. In the RMB, precipitation, streamflow and meteorological data were collected within different historical periods and at diverse temporal resolutions. We designed two statistical tools for downscaling precipitation and potential evapotranspiration data to create the hourly, high-resolution forcing for the hydrologic model from daily records. Despite the presence of several sources of uncertainty in the observations and model parameterization, the use of the disaggregated forcing led to good calibration and validation performances for the tRIBS model, when daily discharge observations were available. The methodology proposed here can be also used to disaggregate outputs of climate models and conduct high-resolution hydrologic simulations with the goal of quantifying the impacts of climate change on water resources and the frequency of hydrologic extremes within medium-sized basins

Investigating parameter transferability across models and events for a Semiarid Mediterranean Catchment

Physically based distributed hydrologic models (DHMs) simulate watershed processes by applying physical equations with a variety of simplifying assumptions and discretization approaches. These equations depend on parameters that, in most cases, can be measured and, theoretically, transferred across different types of DHMs. The aim of this study is to test the potential of parameter transferability in a real catchment for two contrasting periods among three DHMs of varying complexity. The case study chosen is a small Mediterranean catchment where the TIN-based Real-time Integrated Basin Simulator (tRIBS) model was previously calibrated and tested. The same datasets and parameters are used here to apply two other DHMs-the TOPographic Kinematic Approximation and Integration model (TOPKAPI) and CATchment HYdrology (CATHY) models. Model performance was measured against observed discharge at the basin outlet for a one-year period (1930) corresponding to average wetness conditions for the region, and for a much drier two-year period (1931-1932). The three DHMs performed comparably for the 1930 period but showed more significant differences (the CATHY model in particular for the dry period. In order to improve the performance of CATHY for this latter period, an hypothesis of soil crusting was introduced, assigning a lower saturated hydraulic conductivity to the top soil layer. It is concluded that, while the physical basis for the three models allowed transfer of parameters in a broad sense, transferability can break down when simulation conditions are greatly altered

Epistemic Vigilance

Humans massively depend on communication with others, but this leaves them open to the risk of being accidentally or intentionally misinformed. To ensure that, despite this risk, communication remains advantageous, humans have, we claim, a suite of cognitive mechanisms for epistemic vigilance. Here we outline this claim and consider some of the ways in which epistemic vigilance works in mental and social life by surveying issues, research and theories in different domains of philosophy, linguistics, cognitive psychology and the social sciences

Increasing Liana Abundance and Basal Area in a Tropical Forest: The Contribution of Long‐distance Clonal Colonization

Recent evidence suggests that liana abundance and biomass are increasing in Neotropical forests, representing a major structural change to tropical ecosystems. Explanations for these increases, however, remain largely untested. Over an 8‐yr period (1999–2007), we censused lianas in nine, 24 × 36 m permanent plots in old‐growth and selectively logged forest at La Selva Biological Station, Costa Rica to test whether: (1) liana abundance and basal area are increasing in this forest; (2) the increase is being driven by increased recruitment, decreased mortality, or both; and (3) long‐distance clonal colonization explains the increase in liana abundance and basal area. We defined long‐distance clonal colonization as lianas that entered and rooted in the plots as vegetative propagules of stems that originated from outside or above the plot, and were present in 2007, but not in 1999 or 2002. Our hypotheses were supported in the old‐growth forest: mean liana abundance and BA (≥1 cm diameter) increased 15 and 20 percent, respectively, and clonal colonization from outside of the plots contributed 19 and 60 percent (respectively) to these increases. Lianas colonized clonally by falling vertically from the forest canopy above or growing horizontally along the forest floor and re‐rooting—common forms of colonization for many liana species. In the selectively logged forest, liana abundance and BA did not change, and thus the pattern of increasing lianas may be restricted to old‐growth forests. In summary, our data support the hypothesis that lianas are increasing in old‐growth forests, and that long‐distance clonal colonization is a major contributor

A Mutation (G281E) of the Human Uroporphyrinogen Decarboxylase Gene Causes Both Hepatoerythropoietic Porphyria and Overt Familial Porphyria Cutanea Tarda: Biochemical and Genetic Studies on Spanish Patients

Hepatoerythropoietic porphyria is a severe cutaneous porphyria caused by deficiency of uroporphyrinogen decarboxylase and is considered to be the homozygous form of familial (type II) porphyria cutanea tarda. To elucidate further the relation between these conditions, we studied five Spanish families with hepatoerythropoietic porphyria and nine unrelated Spanish patients with familial porphyria cutanea tarda. Immunoreactive and catalytic uroporphyrinogen decarboxylase was decreased by greater than 95% in the five patients with hepatoerythropoietic porphyria. Hepatic uroporphyrinogen decarboxylase activity was decreased to 22% of normal. Four patients were homozygous for a mutation (G281E) originally identified in a Tunisian family; the fifth patient was a compound heterozygote for this mutation. The calculated carrier frequency for G281E in Spain is one in 1800. None of the nine familial porphyria cutanea tarda patients carried the G281E mutation. However, one G281E heterozygote in a family with hepatoerythropoietic porphyria had overt porphyria cutanea tarda. These findings suggest that the G281E mutation is functionally less severe than erythrocyte measurements indicate, that its clinical penetrance is very low in heterozygotes, and that, for this particular mutation, hepatoerythropoietic porphyria is the homozygous form of familial porphyria cutanea tarda

Distributed hydrologic modeling of a sparsely monitored basin in Sardinia, Italy, through hydrometeorological downscaling

The water resources and hydrologic extremes in Mediterranean basins are heavily influenced by climate variability. Modeling these watersheds is difficult due to the complex nature of the hydrologic response as well as the sparseness of hydrometeorological observations. In this work, we present a strategy to calibrate a distributed hydrologic model, known as TIN-based Real-time Integrated Basin Simulator (tRIBS), in the Rio Mannu basin (RMB), a medium-sized watershed (472.5 km2) located in an agricultural area in Sardinia, Italy. In the RMB, precipitation, streamflow and meteorological data were collected within different historical periods and at diverse temporal resolutions. We designed two statistical tools for downscaling precipitation and potential evapotranspiration data to create the hourly, high-resolution forcing for the hydrologic model from daily records. Despite the presence of several sources of uncertainty in the observations and model parameterization, the use of the disaggregated forcing led to good calibration and validation performances for the tRIBS model, when daily discharge observations were available. The methodology proposed here can be also used to disaggregate outputs of climate models and conduct high-resolution hydrologic simulations with the goal of quantifying the impacts of climate change on water resources and the frequency of hydrologic extremes within medium-sized basins

Statistical treatment of looking-time data

Looking times (LTs) are frequently measured in empirical research on infant cognition. We analyzed the statistical distribution of LTs across participants in order to develop recommendations for their treatment in infancy research. Our analyses focused on a common within-subject experimental design, in which longer looking to novel or unexpected stimuli is predicted. We analyzed data from two sources: an in-house set of LTs that included data from individual participants (47 experiments, 1584 observations), and a representative set of published papers reporting group-level LT statistics (149 experiments from 33 papers). We established that LTs are log-normally distributed across participants, and therefore should always be log-transformed before parametric statistical analyses. We estimated the typical size of significant effects in LT studies, which allowed us to make recommendations about setting sample sizes. We show how our estimate of the distribution of effect sizes of LT studies can be used to design experiments to be analyzed by Bayesian statistics, where the experimenter is required to determine in advance the predicted effect size rather than the sample size. We demonstrate the robustness of this method in both sets of LT experiments.This work was supported by an Advanced Investigator Grant (OSTREFCOM) from the European Research Council