Editing IPCC:AR6/WGI/Chapter-12 (section)

=== FAQ 12.3 | How Will Climate Change Affect the Regional Characteristics of a Climate Hazard? ===

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Human-driven climate change can alter the regional characteristics of a climate hazard by changing the magnitude or intensity of the climate hazard, the frequency with which it occurs, the duration that hazardous conditions persist, the timing when the hazard occurs, or the spatial extent threatened by the hazard. By examining each of these aspects of a hazard’s profile change, climate services may provide climate risk information that allows decision makers to better tailor adaptation, mitigation and risk management strategies.

A climate hazard is a climate condition with the potential to harm natural systems or society. Examples include heatwaves, droughts, heavy snowfall events and sea level rise. Climate scientists look for patterns in climatic impact-drivers to detect the signature of changing hazards that may influence stakeholder planning (FAQ 12.1). Climate service providers work with stakeholders and impacts experts to identify key system responses and tolerance thresholds (FAQ 12.2) and then examine historical observations and future climate projections to identify associated changes to the characteristics of a regional hazard’s profile. Climate change can alter at least five different characteristics of the hazard profile of a region (FAQ 12.3, Figure 1):

Magnitude or intensity is the raw value of a climate hazard, such as an increase in the maximum yearly temperature or in the height of flooding that results from a coastal storm with a 1% change of occurring each year.

Frequency is the number of times that a climate hazard reaches or surpasses a threshold over a given period. For example, increases to the number of heavy snowfall events, tornadoes, or floods experienced in a year or in a decade.

Duration is the length of time over which hazardous conditions persist beyond a threshold, such as an increase in the number of consecutive days where maximum air temperature exceeds 35°C, the number of consecutive months of drought conditions, or the number of days that a tropical cyclone affects a location.

Timing captures the occurrence of a hazardous event in relation to the course of a day, season, year, or other period in which sectoral elements are evolving or co-dependent (such as the time of year when migrating animals expect to find a seasonal food supply). Examples include a shift towards an earlier day of the year when the last spring frost occurs or a delay in the typical arrival date for the first seasonal rains, the length of the winter period when the ground is typically covered by snow, or a reduction in the typical time needed for soil moisture to move from normal to drought conditions.

Spatial extent is the region in which a hazardous condition is expected, such as the area currently threatened by tropical cyclones, geographical areas where the coldest day of the year restricts a particular pest or pathogen, terrain where permafrost is present, the area that would flood following a common storm, zones where climate conditions are conducive to outdoor labour, or the size of a marine heatwave.

Hazard profile changes are often intertwined or stem from related physical changes to the climate system. For example, changes in the frequency and magnitude of extreme events are often directly related to each other as a result of atmospheric dynamics and chemical processes. In many cases, one aspect of hazard change is more apparent than others, which may provide a first emergent signal indicating a larger set of changes to come (FAQ 1.2).

Information about how a hazard has changed or will change helps stakeholders prioritize more robust adaptation, mitigation and risk management strategies. For example, allocation of limited disaster relief resources may be designed to recognize that tropical cyclones are projected to become more intense even as the frequency of those storms may not change. Planning may also factor in the fact that even heatwaves that are not record-breaking in their intensity can still be problematic for vulnerable populations when they persist over a long period. Likewise, firefighters recognize new logistical challenges in the lengthening of the fire weather season and an expansion of fire conditions into parts of the world where fires were not previously a great concern. Strong engagement between climate scientists and stakeholders therefore helps climate services tailor and communicate clear information about the types of changing climate hazards to be addressed in resilience efforts.

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'''FAQ 12.3, Figure 1 |''' '''Types of changes to a region’s hazard profile.''' The first five panels illustrate how climate changes can alter a hazard’s intensity (or magnitude), frequency, duration, and timing (by seasonality and speed of onset) in relation to a hazard threshold (horizontal grey line, marked ‘H’). The difference between the historical climate (blue) and future climate (red) shows the changing aspects of climate change that stakeholders will have to manage. The bottom right-hand panel shows how a given climate hazard (such as a current once-in-100-year river flood, geographic extent in blue) may reach new geographical areas under a future climate change (extended area in red).

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