Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

/pdf/climate-change-2007-the-physical-science-basis-1x93ttz9jt.pdf

Climate Change 2007: The Physical Science Basis.

A review of drought concepts

This chapter addresses changes in weather and climate events relevant to extreme impacts and disasters. An extreme (weather or climate) event is generally defined as the occurrence of a value of a weather or climate variable above (or below) a threshold value near the upper (or lower) ends (‘tails’) of the range of observed values of the variable. Some climate extremes (e.g., droughts, floods) may be the result of an accumulation of weather or climate events that are, individually, not extreme themselves (though their accumulation is extreme). As well, weather or climate events, even if not extreme in a statistical sense, can still lead to extreme conditions or impacts, either by crossing a critical threshold in a social, ecological, or physical system, or by occurring simultaneously with other events. A weather system such as a tropical cyclone can have an extreme impact, depending on where and when it approaches landfall, even if the specific cyclone is not extreme relative to other tropical cyclones. Conversely, not all extremes necessarily lead to serious impacts. [3.1] Many weather and climate extremes are the result of natural climate variability (including phenomena such as El Nino), and natural decadal or multi-decadal variations in the climate provide the backdrop for anthropogenic climate changes. Even if there were no anthropogenic changes in climate, a wide variety of natural weather and climate extremes would still occur. [3.1] A changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of weather and climate extremes, and can result in unprecedented extremes. Changes in extremes can also be directly related to changes in mean climate, because mean future conditions in some variables are projected to lie within the tails of present-day conditions. Nevertheless, changes in extremes of a climate or weather variable are not always related in a simple way to changes in the mean of the same variable, and in some cases can be of opposite sign to a change in the mean of the variable. Changes in phenomena such as the El Nino-Southern Oscillation or monsoons could affect the frequency and intensity of extremes in several regions simultaneously.

/pdf/changes-in-climate-extremes-and-their-impacts-on-the-natural-1fikyoq21o.pdf

Changes in climate extremes and their impacts on the natural physical environment.

Changes in climate extremes and their impacts on the natural physical environment: An overview of the IPCC SREX report

Radiative effects of anthropogenic changes in atmospheric composition are expected to cause climate changes, in particular an intensification of the global water cycle with a consequent increase in flood risk. But the detection of anthropogenically forced changes in flooding is difficult because of the substantial natural variability; the dependence of streamflow trends on flow regime further complicates the issue. Here we investigate the changes in risk of great floods--that is, floods with discharges exceeding 100-year levels from basins larger than 200,000 km(2)--using both streamflow measurements and numerical simulations of the anthropogenic climate change associated with greenhouse gases and direct radiative effects of sulphate aerosols. We find that the frequency of great floods increased substantially during the twentieth century. The recent emergence of a statistically significant positive trend in risk of great floods is consistent with results from the climate model, and the model suggests that the trend will continue.

Increasing risk of great floods in a changing climate

This paper documents the record-breaking weather and flooding of winter 2013/14, considers the potential drivers and discusses whether climate change contributed to the severity of the weather and its impacts.

The recent storms and floods in the UK

Observational trend analysis is fundamental for tracking emerging changes in river flows and placing extreme events in their longer-term historical context, particularly as climate change is expected to intensify the hydrological cycle. However, human disturbance within catchments can introduce artificial changes and confound any underlying climate-driven signal. The UK Benchmark Network (UKBN), designated in the early 2000s, comprised a subset of National River Flow Archive (NRFA) stations that were considered near-natural and thus appropriate for identification and interpretation of climate-driven hydrological trends. Here, the original network was reviewed and updated, resulting in the UKBN2 dataset consisting of 146 near-natural catchments. Additionally, the UKBN2 provides user guidance on the suitability of each station for the assessment of low, medium, and high flows. A trend analysis was performed on the updated UKBN2 dataset and results show that while the strength and direction of changes are dependent on the period of record selected, previously detected patterns of river flow change in the UK remain robust for longer periods (>50 years), despite the recent prevalence of extremes. Such a quality assured observational dataset will provide a foundation for future scientific efforts to better understand the changing nature of the hydrological cycle.

/pdf/designation-and-trend-analysis-of-the-updated-uk-benchmark-jk5dwjhtn1.pdf

Designation and trend analysis of the updated UK Benchmark Network of river flow stations: the UKBN2 dataset

Identifying climate-driven trends in river flows on a global basis is hampered by a lack of long, quality time series data for rivers with relatively undisturbed regimes. This is a global problem compounded by the lack of support for essential long-term monitoring. Experience demonstrates that, with clear strategic objectives, and the support of sponsoring organizations, reference hydrologic networks can constitute an exceptionally valuable data source to effectively identify, quantify and interpret hydrological change—the speed and magnitude of which is expected to a be a primary driver of water management and flood alleviation strategies through the future—and for additional applications. Reference hydrologic networks have been developed in many countries in the past few decades. These collections of streamflow gauging stations, that are maintained and operated with the intention of observing how the hydrology of watersheds responds to variations in climate, are described. The status of network...

/pdf/reference-hydrologic-networks-i-the-status-and-potential-20wrwnp1iw.pdf

Reference hydrologic networks I: the status and potential future directions of national reference hydrologic networks for detecting trends

/pdf/2012-from-drought-to-floods-in-england-and-wales-5fvvaiwkrf.pdf

2012: from drought to floods in England and Wales

A remarkably persistent and exceptionally mild cyclonic episode beginning in early-November 2015 and lasting around fourteen weeks brought severe, extensive and protracted flooding which impacted most damagingly on northern Britain, Northern Ireland and parts of Wales. Many existing rainfall and seasonal temperature records were eclipsed during this period and, most notably, maximum recorded river flows were exceeded over a substantial proportion of the country. At the national scale, previous maximum daily and monthly outflows were clearly eclipsed and four relatively discrete episodes of extreme runoff can be recognised. In many areas, the magnitude, persistence and repetitive nature of the flooding had major adverse impacts on communities, infrastructure, agriculture and a host of other sectors of the economy.


The extent and duration of the flooding has very few close parallels in the historical record and, overall, it was a hydrometeorological episode which ranks alongside the 1975/1976 drought and 1947 floods as the most extreme broad-scale events captured in observational records during the last 100 years at least. The truly exceptional runoff patterns experienced in 1947 and 1976 had a major impact on flood and drought management strategies but occurred before the exacerbating impact of climate change was generally recognised. The 2015/2016 flooding, together with the impact of other protracted flood events in the 21st century thus far, has underlined the need to adapt engineering design and flood management strategies to accommodate the recent extension in the range of recorded runoff variability.

The winter floods of 2015/2016 in the UK - a review

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