An emerging tropical cyclone-deadly heat compound hazard

Climate change may bring new hazards through novel combinations of extreme weather (compound events). Here we evaluate the possibility of dangerous heat following major tropical cyclones (TCs) – a combination with serious potential consequences given that mega-blackouts may follow powerful TCs2, and the heavy reliance on air conditioning. We show that “TC-heat” events are already possible along densely populated coastlines globally but, so far, only an estimated 1,000 people have been impacted. However, this number could rise markedly, with over two million at risk under a storyline of the observed TCs recurring in a 2°C warmer world than preindustrial. Using analogues as focussing events we show, for example, that if the catastrophic 1991 Bangladesh Cyclone occurred with 2°C global warming, there would be >70% chance of subsequent dangerous heat. This research highlights a gap in adaptation planning and a need to prepare for an emerging TC-heat compound hazard

Communicating the deadly consequences of global warming for human heat stress

In December of 2015, the international community pledged to limit global warming to below 2 °C above preindustrial (PI) to prevent dangerous climate change. However, to what extent, and for whom, is danger avoided if this ambitious target is realized? We address these questions by scrutinizing heat stress, because the frequency of extremely hot weather is expected to continue to rise in the approach to the 2 °C limit. We use analogs and the extreme South Asian heat of 2015 as a focusing event to help interpret the increasing frequency of deadly heat under specified amounts of global warming. Using a large ensemble of climate models, our results confirm that global mean air temperature is nonlinearly related to heat stress, meaning that the same future warming as realized to date could trigger larger increases in societal impacts than historically experienced. This nonlinearity is higher for heat stress metrics that integrate the effect of rising humidity. We show that, even in a climate held to 2 °C above PI, Karachi (Pakistan) and Kolkata (India) could expect conditions equivalent to their deadly 2015 heatwaves every year. With only 1.5 °C of global warming, twice as many megacities (such as Lagos, Nigeria, and Shanghai, China) could become heat stressed, exposing more than 350 million more people to deadly heat by 2050 under a midrange population growth scenario. The results underscore that, even if the Paris targets are realized, there could still be a significant adaptation imperative for vulnerable urban populations

A cyclone climatology of the British-Irish Isles 1871-2012

The British-Irish Isles (BI) lie beneath the North Atlantic storm track year-round and thus are impacted by the passage of extra-tropical cyclones. Given recent extreme storminess and projections of enhanced winter cyclone activity for this region, there is much interest in assessing the extent to which the cyclone climate of the region may be changing. We address this by assessing a 142-year (1871-2012) record of cyclone frequency, intensity and 'storminess' derived from the 20th Century Reanalysis V2 (20CR) dataset. We also use this long-term record to examine associations between cyclone activity and regional hydroclimate. Our results confirm the importance of cyclone frequency in driving seasonal precipitation totals which we find to be greatest during summer months. Cyclone frequency and storminess are characterized by pronounced interannual and multi-decadal variability which are strongly coupled to atmospheric blocking in the Euro-Atlantic region, but we detect no evidence of an increasing trend. We observe an upward trend in cyclone intensity for the BI region, which is strongest in winter and consistent with model projections, but promote caution interpreting this given the changing data quality in the 20CR over time. Nonetheless, we assert that long-term reconstruction is helpful for contextualizing recent storminess and for identifying emerging changes in regional hydroclimate linked to cyclones

Transferability of hydrological models and ensemble averaging methods between contrasting climatic periods

Understanding hydrological model predictive capabilities under contrasting climate conditions enables more robust decision making. Using Differential Split Sample Testing (DSST), we analyze the performance of six hydrological models for 37 Irish catchments under climate conditions unlike those used for model training. Additionally, we consider four ensemble averaging techniques when examining interperiod transferability. DSST is conducted using 2/3 year noncontinuous blocks of (i) the wettest/driest years on record based on precipitation totals and (ii) years with a more/less pronounced seasonal precipitation regime. Model transferability between contrasting regimes was found to vary depending on the testing scenario, catchment, and evaluation criteria considered. As expected, the ensemble average outperformed most individual ensemble members. However, averaging techniques differed considerably in the number of times they surpassed the best individual model member. Bayesian Model Averaging (BMA) and the Granger-Ramanathan Averaging (GRA) method were found to outperform the simple arithmetic mean (SAM) and Akaike Information Criteria Averaging (AICA). Here GRA performed better than the best individual model in 51%–86% of cases (according to the Nash-Sutcliffe criterion). When assessing model predictive skill under climate change conditions we recommend (i) setting up DSST to select the best available analogues of expected annual mean and seasonal climate conditions; (ii) applying multiple performance criteria; (iii) testing transferability using a diverse set of catchments; and (iv) using a multimodel ensemble in conjunction with an appropriate averaging technique. Given the computational efficiency and performance of GRA relative to BMA, the former is recommended as the preferred ensemble averaging technique for climate assessment

Attribution of detected changes in streamflow using multiple working hypotheses

This paper revisits a widely cited study of the Boyne catchment in east Ireland that attributed greater streamflow from the mid-1970s to increased precipitation linked to a shift in the North Atlantic Oscillation. Using the method of multiple working hypotheses we explore a wider set of potential drivers of hydrological change. Rainfall-runoff models are used to reconstruct streamflow to isolate the effect of climate, taking account of both model structure and parameter uncertainty. The Mann-Kendall test for monotonic trend and Pettitt change point test are applied to explore signatures of change. Contrary to earlier work, arterial drainage and simultaneous onset of field drainage in the 1970s and early 1980s are now invoked as the predominant drivers of change in annual mean and high flows within the Boyne. However, a change in precipitation regime is also present in March, thereby amplifying the effect of drainage. This new explanation posits that multiple drivers acting simultaneously were responsible for the observed change, with the relative contribution of each driver dependant on the timescale investigated. This work demonstrates that valuable insights can be gained from a systematic application of the method of multiple working hypotheses in an effort to move towards more rigorous attribution, which is an important part of managing emerging impacts on hydrological systems. © Author(s) 2014

Using a scenario-neutral framework to avoid potential maladaptation to future flood risk

This study develops a coherent framework to detect those catchment types associated with ahigh risk of maladaptation to futureflood risk. Using the“scenario‐neutral”approach to impactassessment the sensitivity of Irish catchments tofluvialflooding is examined in the context of nationalclimate change allowances. A predefined sensitivity domain is used to quantifyflood responses to +2 °Cmean annual temperature with incremental changes in the seasonality and mean of the annual precipitationcycle. The magnitude of the 20‐yearflood is simulated at each increment using two rainfall‐runoff models(GR4J, NAM), then concatenated as response surfaces for 35 sample catchments. A typology of catchmentsensitivity is developed using clustering and discriminant analysis of physical attributes. The same attributesare used to classify 215 ungauged/data‐sparse catchments. To address possible redundancies, the exposure ofdifferent catchment types to projected climate is established using an objectively selected subset of theCoupled Model Intercomparison Project Phase 5 ensemble. Hydrological model uncertainty is shown tosignificantly influence sensitivity and have a greater effect than ensemble bias. A nationalflood riskallowance of 20%, considering all 215 catchments is shown to afford protection against ~48% to 98% of theuncertainty in the Coupled Model Intercomparison Project Phase 5 subset (Representative ConcentrationPathway 8.5; 2070–2099), irrespective of hydrological model and catchment type. However, results indicatethat assuming a standard national or regional allowance could lead to local over/under adaptation. Herein,catchments with relatively less storage are sensitive to seasonal amplification in the annual cycle ofprecipitation and warrant special attention

An evaluation of persistent meteorological drought using a homogeneous Island of Ireland precipitation network

This paper investigates the spatial and temporal properties of persistent meteorological droughts using the homogeneous Island of Ireland Precipitation (IIP) network. Relative to a 1961–1990 baseline period it is shown that the longest observed run of below average precipitation since the 1850s lasted up to 5 years (10 half-year seasons) at sites in southeast and east Ireland, or 3 years across the network as a whole. Dry spell and wet spell length distributions were represented by a first-order Markov model which yields realistic runs of below average rainfall for individual sites and IIP series. This model shows that there is relatively high likelihood (p = 0.125) of a 5-year dry spell at Dublin, and that near unbroken dry runs of 10 years or more are conceivable. We suggest that the IIP network and attendant rainfall deficit modelling provide credible data for stress testing water supply and drought plans under extreme conditions

Irish droughts in newspaper archives: rediscovering forgotten hazards?

Irish newspaper collections are a rich source of information on historical droughts. Following a search of 250 years of such archives, this paper brings to light four newspaper articles describing three drought events that convey the cultural impacts and unusual societal responses to nineteenth century drought in Ireland. Amongst the archives we find two poems from 1806 and 1893, a call to pray for rain in 1887, and a suggestion for weather modification in 1893. These records demonstrate that, contrary to recent experience, Ireland is surprisingly prone to drought

The “dirty dozen” of freshwater science: Detecting then reconciling hydrological data biases and errors

Sound water policy and management rests on sound hydrometeorological and ecological data. Conversely, unrepresentative, poorly collected or erroneously archived data introduces uncertainty regarding the magnitude, rate and direction of environmental change, in addition to undermining confidence in decision-making processes. Unfortunately, data biases and errors can enter the information flow at various stages, starting with site selection, instrumentation, sampling/ measurement procedures, post-processing and ending with archiving systems. Techniques such as visual inspection of raw data, graphical representation and comparison between sites, outlier and trend detection, and referral to metadata can all help uncover spurious data. Tell-tale signs of ambiguous and/or anomalous data are highlighted using 12 carefully chosen cases drawn mainly from hydrology (‘the dirty dozen’). These include evidence of changes in site or local conditions (due to land management, river regulation or urbanisation); modifications to instrumentation or inconsistent observer behaviour; mismatched or misrepresentative sampling in space and time; treatment of missing values, post-processing and data storage errors. As well as raising awareness of pitfalls, recommendations are provided for uncovering lapses in data quality after the information has been gathered. It is noted that error detection and attribution are more problematic for very large data sets, where observation networks are automated, or when various information sources have been combined. In these cases, more holistic indicators of data integrity are needed that reflect the overall information life-cycle and application(s) of the hydrological data

An investigation into the teaching and learning of probability at senior cycle

In Ireland at present, the National Council for Curriculum and Assessment is comprehensively overhauling the Second Level Mathematics curriculum. This reformed curriculum is known as Project Maths and is a response to concerns about how Irish students are taught and learn mathematics. These concerns are based around the achievement of Irish student’s in international studies (Close and Oldham 2005; Cosgrove, Shiel, Sofroniou, Zastrutzki and Shortt 2005; Perkins, Moran, Cosgrove and Shiel 2010; Oldham 2002, 2006) as well as domestic and international literature which, highlights the problems associated with the behaviourist methodology favoured by Irish teachers (Conway and Sloane 2006; English, O’Donoghue and Bajpai 1992; Lyons, Lynch, Close, Sheerin and Boland 2003; NCCA 2005). The aim of the study was to improve the teaching and learning of Probability through the development of a resource pack. probability was chosen as the focus of the intervention due to the author’s experiences in the classroom, international literature highlighting its pedagogical difficulties (Shaughnessy 1992; Fischbein, Nello and Marino 1991; Ahlgren and Garfield 1988; Hawkins and Kapadia 1984) and its lack of popularity among Irish Leaving Certificate students (Chief Examiner 2000, 2005). The study was designed to examine the benefits of the active learning methodologies and contextualised questions promoted by the Project Maths curriculum, specifically with regards to students’ attitudes and understanding through the implementation and evaluation of a resource pack designed by the author. The evaluation process produced data, which was inconclusive in establishing a link between the promoted methodologies and students’ attitudes and understanding. The only significant shift in students’ attitude was a negative one in response to the statement “I know I can do well in Maths”. A dip in students’ confidence however is not unusual in studies involving changes in pedagogical style (Carpenter, Franke, Jacobs, Fennema and Epsom 1998; Cobb, Wood, Yackel, Nicholls, Wheatley, Trigatti and Perlwitz, 1991; Vershaffel and De Corte 1997; Fauzan et al. 2002; Van Reeuwijk 1992) and though not significant, student scores did improve in the three sub-categories of ‘Perception of Usefulness’, ‘Anxiety’ and ‘Effective Motivation’. There were also indications that these methodologies had a positive effect on understanding. The data also suggested that the resource pack, designed and developed by the author to support the teaching and learning of probability, will be of use to teachers who embrace Project Maths and what it is trying to achieve in Irish classrooms