Figure 23: Analysis of inter-model consistency in regional precipitation change. Regions are classified as showing either agreement on increase with an average change of greater than 20% ('Large increase'), agreement on increase with an average change between 5 and 20% ('Small increase'), agreement on a change between -5 and +5% or agreement with an average change between -5 and 5% ('No change'), agreement on decrease with an average change between -5 and -20% ('Small decrease'), agreement on decrease with an average change of less than -20% ('Large decrease'), or disagreement ('Inconsistent sign'). A consistent result from at least seven of the nine models is deemed necessary for agreement. [Based on Chapter 10, Box 1, Figure 2]
Based on patterns emerging from a limited number of studies with current AOGCMs, older GCMs, and regionalisation studies, there is a strong correlation between precipitation interannual variability and mean precipitation. Future increases in mean precipitation will likely lead to increases in variability. Conversely, precipitation variability will likely decrease only in areas of reduced mean precipitation.
For some other extreme phenomena, many of which may have important impacts on the environment and society, there is currently insufficient information to assess recent trends, and confidence in models and understanding is inadequate to make firm projections. In particular, very small-scale phenomena such as thunderstorms, tornadoes, hail, and lightning are not simulated in global models. Insufficient analysis has occurred of how extra-tropical cyclones may change.
|Table 4: Estimates of confidence in observed and projected changes in extreme weather and climate events. The table depicts an assessment of confidence in observed changes in extremes of weather and climate during the latter half of the 20th century (left column) and in projected changes during the 21st century (right column)a. This assessment relies on observational and modelling studies, as well as physical plausibility of future projections across all commonly used scenarios and is based on expert judgement (see Footnote 4). [Based upon Table 9.6]|
Confidence in observed changes (latter half of the 20th century)
Changes in Phenomenon
Confidence in projected changes (during the 21st century)
|Likely||Higher maximum temperatures and more hot days over nearly all land areas||Very likely|
|Very likely||Higher minimum temperatures, fewer cold days and frost days over nearly all land areas||Very likely|
|Very likely||Reduced diurnal temperature range over most land areas||Very likely|
|Likely, over many areas||Increase of heat index8 over land areas||Very likely, over most areas|
|Likely, over many Northern Hemisphere mid- to high latitude land areas||More intense precipitation eventsb||Very likely, over many areas|
|Likely, in a few areas||Increased summer continental drying and associated risk of drought||Likely, over most mid-latitude continental interiors (Lack of consistent projections in other areas)|
|Not observed in the few analyses available||Increase in tropical cyclone peak wind intensitiesc||Likely, over some areas|
|Insufficient data for assessment||Increase in tropical cyclone mean and peak precipitation intensitiesc||Likely, over some areas|
|a For more details
2 (observations) and Chapters
b For other areas there are either insufficient data or conflicting analyses.
c Past and future changes in tropical cyclone location and frequency are uncertain.
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