Precipitation from persistent extremes is increasing in most regions and globally

Extreme precipitation often persists for multiple days with variable duration but has usually been examined at fixed duration. Here we show that considering extreme persistent precipitation by complete event with variable duration, rather than a fixed temporal period, is a necessary metric to account for the complexity of changing precipitation. Observed global mean annual-maximum precipitation is significantly stronger (49.5%) for persistent extremes than daily extremes. However, both globally observed and modeled rates of relative increases are lower for persistent extremes compared to daily extremes, especially for Southern Hemisphere and large regions in the 0-45°N latitude band. Climate models also show significant differences in the magnitude and partly even the sign of local mean changes between daily and persistent extremes in global warming projections. Changes in extreme precipitation therefore are more complex than previously reported, and extreme precipitation events with varying duration should be taken into account for future climate change assessments

Climate variation in New Zealand and the Southwest Pacific

Climate variation in the New Zealand and Southwest Pacific region is very much a subset of climate variation within the global climate system. The climate in any place over a particular time period is determined by processes within the Earth-atmosphere system, as well as external components. Those regarded as external to the system include the Sun and its solar output, the Sun-Earth geometry, and the Earth's slowly changing orbit around the Sun. These features determine the mean climate, which may vary owing to natural causes within the climate system. The Earth absorbs radiation from the Sun, mainly at the surface. This energy is then redistributed by the circulation of the atmosphere and ocean and radiated to space at longer wavelengths, as described in Chapter 4. On average, for the entire globe, the incoming solar energy is balanced by outgoing terrestrial radiation. Any factor that alters the quantity of radiation received from the Sun or lost to space, or alters the redistribution of energy within the Earth-atmosphere system, can effect climate. Therefore, change in the energy available to the climate system is essentially a radiative forcing

New Zealand is drying out, and here’s why

Over 2012 and 2013, parts of New Zealand experienced their worst drought in nearly 70 years. Drought is the costliest climate extreme in New Zealand; the 2012-2013 event depressed the country’s GDP by 0.7-0.9%. The drought of 1988-1989 affected 5,500 farms, pushing some farmers to the wall. But what does a climate-changed future hold? Recent evidence confirms that New Zealand on the whole is getting dryer. And we’re beginning to understand why — increasing greenhouse and ozone-depleting gases are driving changes in the atmosphere, with impacts far beyond New Zealand. A history of drought Agricultural drought is occurs when there is not enough moisture in the soil available to support crop and pasture growth. It is usually fairly extensive over significant parts of the country. In March this year we reported that there is distinct trend towards increased agricultural drought since 1941, in four (80%) out of the five agricultural drought regions. There is a trend toward a summer drying in all of these regions except the west of the North Island. The overall trend for New Zealand agricultural drought is shown in the diagram below.   New Zealand agricultural drought index 1941-2013 averaged over the country. The bars represent individual years, and the straight line shows the 72-year trend. Positive values mean a droughtier year, and negative values mean a wetter year for agriculture.   What’s causing the big dry? Two recent reports shed light on why drought is increasing in New Zealand. On 9 September the Geneva based World Meteorological Organization (WMO), a United Nations body, announced that the amount of greenhouse gases in the atmosphere reached a new record high in 2013, propelled by a surge in levels of carbon dioxide during between 2012 and 2013. Last year the concentration of CO2 in the atmosphere reached 142% of the pre-industrial era (1750). Methane levels reached 253% and nitrous oxide 121%. Between 1990 and 2013 there was a 34% increase in radiative forcing — the warming effect on our climate — because of long-lived greenhouse gases such as carbon dioxide (CO2), methane and nitrous oxide. These have warmed the climate. Over the last 72 years mean annual global and New Zealand temperatures have increased by 0.6 and 0.7C respectively. And on September 11 a new report, with Dr Olaf Morgenstern of the NZ National Institute of Water and Atmospheric Research as a reviewer recognised the role of ozone depletion in drying parts of southern Australia. The same link has been established in New Zealand. Ozone depletion affects an atmospheric pattern known as the Southern Annular Mode, or SAM. These changes are particularly pertinent as the spring time stratospheric Antarctic ozone hole peaked this year at 24 million square kilometres on September 11. SAM describes the movement of the westerly wind belt that circles the Southern Oceans between the South Island of New Zealand and Antarctica. In its positive phase, SAM causes the belt of strong westerly winds to contract towards Antarctica. There are weaker westerly winds than normal over the South Island with higher pressures, and less cold fronts crossing New Zealand. The opposite occurs in the negative phase of SAM with the westerly wind belt expanded north towards New Zealand and the passage of more westerly cold fronts. The positive SAM has also been linked to decreasing rainfall in south western Australian, and the recent record-breaking expansion of Antarctic sea ice.   Index of the Southern Annular Mode, 1957 – 2013. Source: British Antarctic Survey, Cambridge, UK.   The graph of SAM over the last 56 years shows a trend towards a more positive index, averaging around -3 at the beginning of the record to +1 in recent years. Several researchers have now shown that this increase in SAM is strongly associated with stratospheric ozone depletion. Less rain, more evaporation Recent work has revealed that changes in SAM in New Zealand have resulted in a weakening of moisture laden westerly winds during the summer, and increased high pressures over the North Island with less rain. The warming trend caused by increasing greenhouse gases has led to more moisture loss to the atmosphere from plants because of increased evapotranspiration. This is where plants “breathe out” into the air moisture that is stored in the soil. The hotter it is, the more moisture plants pump out into the atmosphere. These two effects — less rainfall and more water loss from the soil have resulted in our climate becoming droughtier for agricultural activities. Bringing back the rains The stratospheric ozone layer is now protected by the Montreal Protocol — an international treaty to protect the ozone layer by phasing out production of ozone-depleting substances signed in 1989. Unfortunately it has not prevented some impacts on New Zealand climate — but at least these impacts will be slowed then reversed in coming decades. The Antarctic stratospheric ozone hole peaked in 2006 at around 30 million square kilometres. However there is no such robust agreement to curb the growth of greenhouse gases in the atmosphere. The World Meteorological Organisation has called for even greater urgency for concerted international action against accelerating and potentially devastating climate change. Any future New Zealand government must front up to New Zealand taking full leadership in any international agreements to rapidly halt and reverse the growth of greenhouse gases, as the country did with the Montreal Protection to protect the stratospheric ozone layer twenty five years ago. After all, these trends are now affecting the country’s land-based industries vital for its wealth. Jim Salinger does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations. This article was originally published on The Conversation. Read the original article. Photo: Dave Young / Flick

Australia and New Zealand

http://trove.nla.gov.au/work/3234109

Globally observed annual precipitation maxima

This data is used to analyse the changes in the observed global extreme daily and persistent precipitation.Peer reviewe

Extreme precipitation on consecutive days occurs more often in a warming climate

Extreme precipitation occurring on consecutive days may substantially increase the risk of related impacts, but changes in such events have not been studied at a global scale. Here we use a unique global dataset based on in situ observations and multimodel historical and future simulations to analyze the changes in the frequency of extreme precipitation on consecutive days (EPCD). We further disentangle the relative contributions of variations in precipitation intensity and temporal correlation of extreme precipitation to understand the processes that drive the changes in EPCD. Observations and climate model simulations show that the frequency of EPCD is increasing in most land regions, in particular, in North America, Europe, and the Northern Hemisphere high latitudes. These increases are primarily a consequence of increasing precipitation intensity, but changes in the temporal correlation of extreme precipitation regionally amplify or reduce the effects of intensity changes. Changes are larger in simulations with a stronger warming signal, suggesting that further increases in EPCD are expected for the future under continued climate warming.M.G.D. acknowledges support by the Horizon 2020 EUCP project under Grant Agreement 776613 and by the Spanish Ministry for the Economy, Industry and Competitiveness Ramón y Cajal 2017 Grant Reference RYC-2017-22964

Extreme precipitation on consecutive days occurs more often in a warming climate

Extreme precipitation occurring on consecutive days may substantially increase the risk of related impacts, but changes in such events have not been studied at a global scale. Here we use a unique global dataset based on in situ observations and multimodel historical and future simulations to analyze the changes in the frequency of extreme precipitation on consecutive days (EPCD). We further disentangle the relative contributions of variations in precipitation intensity and temporal correlation of extreme precipitation to understand the processes that drive the changes in EPCD. Observations and climate model simulations show that the frequency of EPCD is increasing in most land regions, in particular, in North America, Europe, and the Northern Hemisphere high latitudes. These increases are primarily a consequence of increasing precipitation intensity, but changes in the temporal correlation of extreme precipitation regionally amplify or reduce the effects of intensity changes. Changes are larger in simulations with a stronger warming signal, suggesting that further increases in EPCD are expected for the future under continued climate warming.https://journals.ametsoc.org/view/journals/bams/bams-overview.xml2022-12-09dm2022Geography, Geoinformatics and Meteorolog