Developing Intensity-Duration-Frequency (IDF) Curves From Satellite-Based Precipitation: Methodology and Evaluation

Given the continuous advancement in the retrieval of precipitation from satellites, it is important to develop methods that incorporate satellite-based precipitation data sets in the design and planning of infrastructure. This is because in many regions around the world, in situ rainfall observations are sparse and have insufficient record length. A handful of studies examined the use of satellite-based precipitation to develop intensity-duration-frequency (IDF) curves; however, they have mostly focused on small spatial domains and relied on combining satellite-based with ground-based precipitation data sets. In this study, we explore this issue by providing a methodological framework with the potential to be applied in ungauged regions. This framework is based on accounting for the characteristics of satellite-based precipitation products, namely, adjustment of bias and transformation of areal to point rainfall. The latter method is based on previous studies on the reverse transformation (point to areal) commonly used to obtain catchment-scale IDF curves. The paper proceeds by applying this framework to develop IDF curves over the contiguous United States (CONUS); the data set used is Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks – Climate Data Record (PERSIANN-CDR). IDFs are then evaluated against National Oceanic and Atmospheric Administration (NOAA) Atlas 14 to provide a quantitative estimate of their accuracy. Results show that median errors are in the range of (17–22%), (6–12%), and (3–8%) for one-day, two-day and three-day IDFs, respectively, and return periods in the range (2–100) years. Furthermore, a considerable percentage of satellite-based IDFs lie within the confidence interval of NOAA Atlas 14

Time-dependent Stochastic Modeling of Solar Active Region Energy

A time-dependent model for the energy of a flaring solar active region is presented based on a stochastic jump-transition model (Wheatland and Glukhov 1998; Wheatland 2008; Wheatland 2009). The magnetic free energy of the model active region varies in time due to a prescribed (deterministic) rate of energy input and prescribed (random) flare jumps downwards in energy. The model has been shown to reproduce observed flare statistics, for specific time-independent choices for the energy input and flare transition rates. However, many solar active regions exhibit time variation in flare productivity, as exemplified by NOAA active region AR 11029 (Wheatland 2010). In this case a time-dependent model is needed. Time variation is incorporated for two cases: 1. a step change in the rates of flare jumps; and 2. a step change in the rate of energy supply to the system. Analytic arguments are presented describing the qualitative behavior of the system in the two cases. In each case the system adjusts by shifting to a new stationary state over a relaxation time which is estimated analytically. The new model retains flare-like event statistics. In each case the frequency-energy distribution is a power law for flare energies less than a time-dependent rollover set by the largest energy the system is likely to attain at a given time. For Case 1, the model exhibits a double exponential waiting-time distribution, corresponding to flaring at a constant mean rate during two intervals (before and after the step change), if the average energy of the system is large. For Case 2 the waiting-time distribution is a simple exponential, again provided the average energy of the system is large. Monte Carlo simulations of Case~1 are presented which confirm the analytic estimates. The simulation results provide a qualitative model for observed flare statistics in active region AR 11029.Comment: 25 pages, 9 figure

The central European floods of August 2002: Part 1 - Rainfall periods and flood development

Record-breaking rainfall amounts and intensities were observed at several raingauges in central Europe during the first half of August 2002 (Fig. 1). They produced flash floods in small rivers in the Erz Mountains, the Bohemian Forest and in Lower Austria (see Fig. 2), followed by record-breaking floods of larger rivers fed from these areas. The Vltava submerged parts of the city of Prague on 13± 15 August, and subsequently the Elbe flooded parts of Dresden and further villages and towns located downstream. The gauge level of 9.40m measured at Dresden on 17 August 2002 is the highest level since 1275, exceeding the former maximum level of 8.77m recorded in 1845 (Grollmann and Simon 2002). Parts of the Danube catchment were also affected by severe flooding. There were 100 fatalities connected with the floods in central Europe, and the economic loss is estimated at 9 billion Euros for Germany (German government’s estimate), 3 billion Euros for Austria, and 2.5 billion Euros for the Czech Republic (estimates from Boyle 2002). The event thus replaced the European winter storm Lothar of December 1999 (Ulbrich et al. 2001) as the most expensive weather-related catastrophe in Europe in recent decades (see Cornford 2002). In this study, we give an overview of the exceptional rainfall experienced over wide areas on 12/13 August 2002, and the resulting floods. Further events during early August 2002, in particular the event on 6/7 August in Lower Austria, are briefly mentioned

The credibility challenge for global fluvial flood risk analysis

Quantifying flood hazard is an essential component of resilience planning, emergency response, and mitigation, including insurance. Traditionally undertaken at catchment and national scales, recently, efforts have intensified to estimate flood risk globally to better allow consistent and equitable decision making. Global flood hazard models are now a practical reality, thanks to improvements in numerical algorithms, global datasets, computing power, and coupled modelling frameworks. Outputs of these models are vital for consistent quantification of global flood risk and in projecting the impacts of climate change. However, the urgency of these tasks means that outputs are being used as soon as they are made available and before such methods have been adequately tested. To address this, we compare multi-probability flood hazard maps for Africa from six global models and show wide variation in their flood hazard, economic loss and exposed population estimates, which has serious implications for model credibility. While there is around 30-40% agreement in flood extent, our results show that even at continental scales, there are significant differences in hazard magnitude and spatial pattern between models, notably in deltas, arid/semi-arid zones and wetlands. This study is an important step towards a better understanding of modelling global flood hazard, which is urgently required for both current risk and climate change projections

Natural and human-induced coastal dynamics at a back-barrier beach

This study contributes to the understanding of very low-energy fetch-limited environments by reporting the evolution of a back-barrier beach (Ancão Peninsula, southern Portugal). It considers two timescales: a large-scale evolution for the past 60 years based on aerial photograph analysis, and a small-scale beach evolution based on monthly topographic surveys performed during three years of monitoring. Each timescale revealed a different rate of evolution, the first reporting a modified beach response-type (from human activities), and the second reporting a natural beach response-type. Human activities caused significant changes in the back-barrier shore, whereas changes under natural forcing were much smaller, were less influential on the area's evolution, and were not sufficient to counteract or mask the consequences of human activities. The findings of the study should contribute to a better understanding about the large- and small- scale changes in other back-barriers characterised by similar very low-energy conditions.info:eu-repo/semantics/publishedVersio

Weather, disease, and wheat breeding effects on Kansas wheat varietal yields, 1985 to 2011.

Wheat (Triticum aestivum L.) yields in Kansas have increased due to wheat breeding and improved agronomic practices, but are subject to climate and disease challenges. The objective of this research is to quantify the impact of weather, disease, and genetic improvement on wheat yields of varieties grown in 11 locations in Kansas from 1985 to 2011. Wheat variety yield data from Kansas performance tests were matched with comprehensive location-specific disease and weather data, including seasonal precipitation, monthly air temperature, air temperature and solar radiation around anthesis, and vapor pressure deficit (VPD). The results show that wheat breeding programs increased yield by 34 kg ha⁻¹ yr⁻¹. From 1985 through 2011, wheat breeding increased average wheat yields by 917 kg ha⁻¹, or 27% of total yield. Weather was found to have a large impact on wheat yields. Simulations demonstrated that a 1°C increase in projected mean temperature was associated with a decrease in wheat yields of 715 kg ha⁻¹, or 21%. Weather, diseases, and genetics all had significant impacts on wheat yields in 11 locations in Kansas during 1985 to 2011

Trophic positioning of meiofauna revealed by stable isotopes and food-web analyses

Despite important advances in the ecology of river food-webs, the strength and nature of the connection between the meio- and macrofaunal components of the web are still debated. Some unresolved issues are the effects of the inclusion of meiofaunal links and their temporal variations on the overall river food web properties, and the significance of autochtonous and allochtonous material for these components. In the present study we conducted gut content of macro- and meiofauna, and stable isotope analyses of meiofauna to examine seasonal food webs of a chalk stream. The results of the gut content analyses, confirmed by the δ13C signatures, revealed a seasonal shift from a dependence on autochthonous (biofilm) to allochthonous food sources. Here, we demonstrate that aggregating basal or meiofaunal species into single categories affects key web properties such as web size, links, linkage density, and predator-prey ratios. More importantly, seasonal variation in attributes characterized the entire web and these changes persist regardless of taxonomic resolution. Furthermore, our analyses evidenced discrete variations in δ15N across the meiofauna community with a trophic structure that confirms gut content analyses, placing the meiofauna high in the food web. We, therefore, conclude that small body-sized taxa can occur high in dynamic river food webs, questioning assumptions that trophic position increases with body size and that webs are static

Farmer’s perception of climate change and responsive strategies in three selected provinces of South Africa

The world has responded to climate change phenomenon through two broad response mechanisms (mitigation and adaptation strategies) with the aim of moderating the adverse effects of climate change and/or to exploit any arising beneficial opportunities. The paper aims to examine the trend in climate parameters, farmers’ perception of climate change, constraints faced in production and to identify the strategies (if any) that farmers have adopted to cope with the effects of changing climate. A one-way analysis of variance, percentage analysis and Garrett ranking technique were applied to a set of primary data collected from 150 randomly sampled farmers with the aid of questionnaires in three purposively selected provinces through the months of June to August 2015. The analytical results of obtained recent weather data revealed that the climate parameters have significantly changed over time and these were substantiated by farmers’ experiences. The farmers are engaging in various climate-response strategies, among which, the planting of drought-tolerant varieties is most common. Therefore, it is important to enhance farmers’ access to improved drought-tolerant seeds and efficient irrigation systems. Also observed, is that the lack of awareness of insurance products and inability to afford insurance premiums were the principal reasons majority of the farmers did not have insurance. These present a need to strengthen insurance adoption among farmers through various supporting programmes that may include premium subsidies and media outreach. The paper under one platform provides evidence of changing climate, farmers’ responses towards mitigating perceived adverse effects of the changed climate, and South Africa’s national policy on adaptation and mitigation