Search

In the current context of climate change, the increase in minimum temperatures recorded in recent decades has received special scientific attention due to its importance for the proper night's sleep and health of the population, among other considerations. One of the main indicators usually considered refers to the frequency of tropical nights (≥20°C), which have begun to become widespread in regions hitherto excluded from this type of event. This paper analyses tropical nights in Spain between 1970 and 2023, addressing their mean annual occurrence, their intensity, their monthly distribution and the average number of consecutive tropical nights recorded, as well as their relationship with relative humidity. The results, based on the analysis of 75 homogenized series located in 44 different provinces, allow us to differentiate seven large areas based on the minimum temperature in which there has been an increase in the frequency and intensity of tropical nights, which progressively extend the season in which they can appear. Similarly, a generalized increase in the maximum number of consecutive nights thermally above 20°C was identified, in addition to the presence of high relative humidity in coastal areas during these episodes. [ABSTRACT FROM AUTHOR]

In this paper we analyse the relationship between the mean and extreme precipitation for five stations in Hungary and the circulation types at the 500 hPa level, for a 52‐year period, 1958–2010. We used daily rainfall data for each station and a calendar of the daily circulation types at the 500 hPa geopotential height for Hungary based on an automatic classification scheme. A trend analysis showed that, in general, the mean and extreme precipitation rarely exhibit significant trends, similarly to previous studies. The only exception was found for the number of annual and summer rainy days in Budapest with significant negative trends (p = .05), as well as the number of days with rainfall amounts greater than the 95% probability level for Debrecen with a significant positive trend. It was found that the circulation types that are mainly responsible for the largest precipitation amounts overall show (in some cases significant) negative trends, as well as the precipitation amounts that are associated with them (Cwsw, Cse, Cwnw). In most cases, the circulation types that are prevailing during the extreme precipitation events are associated with western or almost‐western atmospheric circulations (Cwsw, Ase) and Mediterranean‐ or Atlantic‐origin depressions. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper documents the changes in climate extremes over Indonesia during the past three decades (1983-2012) based on a subset of extreme indices recommended by the Expert Team on Climate Change Detection and Indices ( ETCCDI). The extreme indices were calculated based on the quality controlled daily observational data (minimum and maximum temperature and precipitation) from 88 weather stations. Overall, we found significant and spatially coherent trends of warming in the temperature indices over Indonesia, consistent with other studies conducted at different countries within the Southeast Asia. The frequency of cool days ( TX10p) and cools nights ( TN10p) had decreased whereas warm days ( TX90p) and warm nights ( TN90p) were observed more frequently. Averaged over the country, the annual mean of daily maximum ( TXmean) and minimum temperature ( TNmean) had increased significantly by 0.18 and 0.30 °C decade−1, respectively. Other temperature indices also showed significant warming trends. In contrast, trends in the precipitation extremes indices were generally not significant and less spatially coherent. However, a tendency towards wetter conditions was observed, in agreement with the results at the global scale. The daily precipitation intensity ( SDII) had increased significantly over the country by 0.21 mm day−1 decade−1 during the period studied. At the regional scale, we observed a significant wetting trend in the annual highest daily amount ( RX1day) and the rainfall amount contributed by the extremely very wet days (R99p) in the northern part of the country. The wetting trends of a number of extreme precipitation indices were depicted prominently in December-January-February ( DJF) and/or March-April-May ( MAM) seasons, both at country and regional levels. However, for the southern region of Indonesia, a drying tendency was observed for June-July-August ( JJA), September-October-November ( SON) and MAM. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper presents an analysis of winter climate variability based on daily mean temperature and precipitation data since 1970 in the Chic-Chocs Mountain range (located in the Gaspé Peninsula, Eastern Quebec, Canada). Mountain environments are particularly sensitive to rapid climate change and are therefore good indicators of recent global warming. The main goal of this study is to demonstrate how joint probability temperature/precipitation distributions can be used to estimate winter condition changes (trends) for six meteorological stations in the study area (the altitudinal range for the stations is from 5 to 574 m). The presence and persistence of snow cover was also estimated. Previous studies have shown a lack of evidence of significant trends in snow-cover characteristics (density, depth and snow water equivalent (SWE)) from the early 1980s to the present, despite an increase in temperature over the same period. A reanalysis of these data sets in addition to the use of a combination of temperature and precipitation data categorized into four modes (warm/wet, warm/dry, cold/wet and cold/dry) was also performed. Despite this new analysis, no clear evidence of climate change could be found in the study area over the last four decades. The results revealed that patterns and trends are quite different from one station to another, but when the environment is taken into account (valley or plateau, coastal versus inland) some apparent patterns emerge. [ABSTRACT FROM AUTHOR]

In the context of climate change characterized by rising temperature and more extreme precipitation regimes, drought is one of the most relevant natural disasters. This paper presents maps of global drought frequency, duration, and severity for the periods 1951-1970, 1971-1990, and 1991-2010, to give an overview of the respective drought hot spots. Drought frequency is defined as the number of drought events occurred, drought duration as the number of months in drought conditions, and drought severity as the sum of the integral area below zero of each event. Because drought is mainly driven by rainfall deficits, we chose the Standardized Precipitation Index (SPI) as the base indicator to derive drought-related quantities. SPI-12 has been calculated on a monthly basis using a Gamma distribution fitted to a 60-year baseline period (1951-2010). Global grids (0.5° ×0.5°) of the Full Data Reanalysis Version 6.0 dataset provided by the Global Precipitation Climatology Centre (GPCC) have been used as precipitation data input. The regions most exposed to prolonged and severe droughts during 1951-1970 were the Central United States, the Argentinian Pampas, Russia, and Central Australia; during 1971-1990 they were Southern Chile, the Sahel, and Siberia; during 1991-2010 they were the Amazon Forest, the Congo River Basin, Mongolia, North Eastern China, and Borneo. A linear trend analysis between 1951 and 2010 shows a small global increase in each drought component, but drought frequency decreased in the Northern Hemisphere. The increase in drought frequency, duration, and severity is found to be significant in Africa, Eastern Asia, Mediterranean region, and Southern Australia, while the Americas and Russia show a decrease in each drought component. [ABSTRACT FROM AUTHOR]

ABSTRACT In a recent article, Diem (2012) examined the impact of the North Atlantic Subtropical High ( NASH) and atmospheric moistening on summer rainfall variability in the Atlanta, Georgia region. In his paper, he indicated that the results concerning the variability of the NASH western ridge discussed in Li et al. (2011) are incorrect. We present new evidence here to show that the comments by Diem (2012) are unjustified; the main conclusions in Li et al. (2011) were drawn according to the data over a 60-year (1948-2007) and 45-year (1958-2002) periods of NCEP/ NCAR and ERA-40 reanalysis, whereas conclusions of Diem (2011) were based upon the trend analysis of a similar but different index of the NASH using sub-periods of 1948-2009 (since late 1970s). The comment emphases the importance of climate dynamics to study precipitation variability over the Southeastern US and further strengthens the conclusions originally put forth in Li et al. (2011): over the last 60 years (1948-2007), the NASH has shown a significant trend of westward movement, and the meridional movement of the NASH western-ridge (i.e. its latitudinal change) has enhanced in the recent three decades. [ABSTRACT FROM AUTHOR]

This study investigates the long‐term variability of surface air temperature (SAT) over the Arabian Peninsula (AP), using data from the Climate Research Unit (TS 3.22) for the 1960–2010 period. The long‐term climatology suggests that the warmest AP mean temperatures occur during summer, with the highest temperatures over the northern AP (NAP), due to the monsoon–desert mechanism. During winter, the NAP exhibits low SATs under the influence of western disturbances originating from the Mediterranean. The southwestern AP exhibits the lowest temperatures because of its proximity to the Arabian Sea cold waters, and also because of the orographic effects. The inter‐annual variability of the SAT is stronger during winters. A linear trend analysis reveals a significant increase in the SAT anomaly (0.10 °C/decade) across the AP, consistently with the global temperature anomalies. Besides the local convective heating, summer SAT variability is associated with the weakening of the Asian jet stream and a Rossby wave train from the Indian Ocean. This variability is also influenced by the anomalous low pressure over the North Atlantic and the Sahara, a high‐pressure system over Siberia and the northwest Pacific. Both in spring and autumn, sea surface temperature (SST) variations over the Indo‐western Pacific are highly influenced the AP SATs, whereas winter SATs are modulated by the subtropical jet stream and the Middle East jet stream. In all seasons, the AP SAT is strongly influenced by the SST variations over the tropical oceans. The temperature variability is closely associated with the El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). The warm phase of ENSO (i.e., El Niño) is one possible reason behind the inter‐annual increase in SAT over the southern AP. The negative phases of NAO and AO also play a role in increasing AP SAT. Seasonal and annual mean surface air temperature (°C, shaded) and standard deviation (contours) over the Arabian Peninsula for the period 1960–2010. [ABSTRACT FROM AUTHOR]

Non‐meteorological factors may bias wind speed measurements in a number of ways, among them the types of instruments used, their calibration and standards of maintenance, station relocations, and changes in the physical surroundings of a given station. Moreover, homogenisation of series of such measurements is more complicated than that of other climatic variables. This contribution uses figures from the Czech Republic as an example to demonstrate that measured (raw) data may produce different results in mean daily wind speeds from those acquired in homogenous series. A basic set of measurements taken in 1961–2015 at 178 meteorological stations was quality‐checked and then homogenized using the Standard Normal Homogeneity test (SNHT) and the Maronna‐Yohai test. Subsequent analyses were based on homogenized series from 119 stations. Station relocations and automation of wind speed measurements were identified as the most important sources of break‐points in series of mean daily wind speeds. Generally lower mean wind speeds (as well as wind speed variability) were obtained from homogenous series in comparison with measured data, with reflections also found in their spatial distribution around the territory of the Czech Republic. Statistically significant decreasing linear trends calculated from measured and homogenized daily wind speed series from 119 stations confirm the existence of wind stilling as a typical feature of land mid‐latitudes in recent decades. However, trends from measured data are highly overestimated compared with those from homogenized series. Fluctuations in mean annual wind speed series based on measured (1) and homogenized (2) data in the 1961–2015 period for four altitudinal groups (I: ≤300 m asl, II: 301–600 m asl, III: 601–900 m asl, IV: >900 m asl) and the entire Czech Republic (CR). Linear trends and their values (m s−1 dec−1; left below) for both types of series are included [ABSTRACT FROM AUTHOR]

A comprehensive analysis of the spatial and temporal variability of daily precipitation in Spain in the period 1950–2012 was carried out based on the high‐resolution gridded data set SPREAD at a 5 × 5 km spatial resolution. Temporal trends of 12 daily precipitation indices were computed by application of the Sen's slope and the Mann–Kendall tests. The spatial distribution of the trends showed (a) a global slight increase in the duration of the precipitation events, especially along the Mediterranean fringe; (b) an increase of the frequency of low precipitation events and a decrease of the frequency of high and very high events (inverse in the Mediterranean coast); and (c) a slight decrease of the intensity when considering single events (1‐ or 5‐day duration), but a significant negative trend in mean and median precipitation when considering all the precipitation days (p > 0), especially in the Mediterranean coast. [ABSTRACT FROM AUTHOR]

High‐resolution numerical simulations were carried out for the most recent 30‐year period (1987–2016), focusing on the Euro‐Mediterranean region. A sophisticated thermo‐physiologically significant thermal index, namely the physiologically equivalent temperature (PET), was computed for assessing the thermal bioclimate of the study area and for investigating the presence of long‐term trends, focusing on bioclimatic extremes. Results indicate that the Euro‐Mediterranean thermal bioclimate follows a zonal pattern, upon which topography acts to delineate regional maxima and minima. The conducted time series analysis reveals statistically significant trends that are generally more pronounced for cold extremes. In particular, it is found that the number of days with cold (hot) stress has decreased (increased), with the distribution of PET exhibiting warming of both its cold and warm tail. The south–east Mediterranean and the Balkans are found to be the most responsive to bioclimatic changes, showing coherent and statistically significant warming trends. Overall, the results of this study provide a new point of view of the Euro‐Mediterranean climate, which could be of usefulness in a wide range of future applications. The detailed spatio‐temporal bioclimatic data could be exploited, for instance, to support applications related to tourism and recreation, highlighting regions with favourable or less favourable thermal comfort conditions. Furthermore, the trend data could be employed for quantifying the vulnerability of certain regions to cold and heat stress, in the context of public health applications. [ABSTRACT FROM AUTHOR]

We present the Caribbean's Virgin Islands’ climate variability over the last 60 years from indices of extreme temperature and precipitation, as well as their quantitative support for a recent climatic shift (1983.2 ± 5.5 years). The region's climate indices (defined via time series averages) and trends (defined via linear least squares regression fitting) of extreme temperature and precipitation were cross‐examined from 1952, 1961, 1978, and 1983–2014 to diagnose: the area's climatic extremes; a climatic transition's role in assessing decadal climate anomaly rates; and to provide an analytically independent test of the transition's existence. Analyses relied on the use of varying physical constraints to include weighting from statistical and non‐statistical uncertainties in our climatic outcomes. We report that diurnal warming and enhanced precipitation accompanied each interval, however, non‐negligible deviations existed in comparisons between the same anomalies in any 2 intervals. Our Virgin Islands’ long (1952, 1961–2014) versus short (1978, 1983–2014) climate variation comparisons provide evidence for the manifestation of decadal (or longer) shifts, and thus, biases, in recent Caribbean reports. Our climatic transition's overlap with the renowned 1976/1977 Pacific event insinuates a local Caribbean teleconnection, and contributes to the evidence growing globally for 1980s’ shifts in an abundance of feedback measures of Earth's energy budget. [ABSTRACT FROM AUTHOR]

ABSTRACT: Observational analyses of changing climate extremes over the West Africa region have been limited by the availability of long and high‐quality datasets. To help address this gap, a climate extremes indices workshop was held in the Gambia in December 2011 with participants from 14 West African countries. The resulting analysis utilized 15 annual indices derived from observed daily temperatures and 10 annual indices derived from observed daily precipitation. The analysis was conducted for 166 meteorological stations in 13 countries for 2 periods: 1960–2010 and 1981–2010. The analyses of trends in the annual mean temperature indices have identified statistically significant increases of 0.16 °C/decade and 0.28 °C/decade for mean annual maximum and mean annual minimum temperatures, respectively, averaged over all available land stations in the region during the last 50 years. The seasonal‐temperature‐related indices show significant patterns of warming in all seasons. The annual mean of daily minimum temperature has increased more than the annual mean of daily maximum temperature leading to a decreasing trend in the diurnal temperature range. Warm days and warm nights have become more frequent, and cold days and cold nights have become less frequent. The analyses of precipitation‐based indices indicate spatially non‐coherent changes throughout the study area with few statistically significant trends over the longer period. Exceptions to this are the simple daily intensity index and maximum 5‐day precipitation, which show significant increasing regional trends over both the shorter and longer periods. Additionally, over the recent period (1981–2010) most of the precipitation related indices show significant trends towards wetter conditions. However, this period of increased rainfall follows a decade of significantly drier conditions in the region – it is not clear whether the recent upward trends reflect the ‘recovery’ from this long drought period or represents a long‐term response to warming. [ABSTRACT FROM AUTHOR]

ABSTRACT Quantifying precipitation variability and trends is difficult and merits regular reassessment. In the present study, the seasonal homogenized precipitation series in Switzerland is investigated for the period 1901-2013 in terms of trends, inter-annual variability and the influence of large-scale flow. An objective clustering is applied, resulting in 32 distinct precipitation regions. Trends are analysed for all 32 regions with moving trend windows, and statistical significance ( p < 0.05) is assessed with Theil-Sen trend estimates and nonparametric Mann-Kendall trend tests. Inter-annual precipitation varies considerably regionally and seasonally. Of 2720 analysed trend windows of 33-113 years in length, 194 (7.1%) show a significantly positive trend and 10 (0.4%) a significantly negative trend. Most of the significantly positive trends are found for 50+ year series for winter, autumn and the year. 81% of the annual and 72% of the winter series show positive trends (0-3% per decade) for the 1901-2013 period. The trends are significant for 34% (22%) of the annual (winter) series. Long-term trends are generally in line with earlier estimates in literature considering somewhat shorter time periods. Significantly negative trends are only found for winter in the most recent decades. No significant trends are found for inter-annual variability and changes in the 10th and 90th percentile seasonal extreme precipitation thresholds. The influence of large-scale flow on precipitation variability is strongest in winter. The leading pattern for northern Switzerland ( nS) is the Euro-Atlantic blocking pattern. For southern Switzerland ( sS), the Eastern Atlantic (Scandinavian) pattern is dominant in winter (autumn). In nS, wet (dry) seasons are linked to south-westerly (north-easterly) flow. In sS, wet (dry) seasons are linked to southerly (northerly) flow. Strong evidence for imprints of atmospheric blocking on seasonal precipitation variability is found in winter and autumn. In spring, a high pressure anomaly stretching from the mid-Atlantic to central Europe is indicative of dryness in nS. [ABSTRACT FROM AUTHOR]

ABSTRACT Trends of annual maximum 1-day precipitation in three major Hawaiian Islands are investigated using a nonparametric Mann-Kendall method and Sen's test ( MKS). The records are from 24 stations on Oahu, Maui, and Hawaii, and the period of analysis ranges from 1960 to 2009. To complement the MKS method, a non-stationary three-parameter generalized extreme value ( GEV) distribution is also used to detect trends in precipitation extremes. Both methods demonstrate that negative trends prevail for Oahu and Maui but positive trends dominate the Island of Hawaii. The influence of the location and the scale parameter in the GEV model on different return levels (2-year, 20-year, and 100-year) are explicitly described. The return-level threshold values are found to change with time considerably. As a result, a rare storm with daily precipitation of 300 mm (20-year return period) in 1960 has become a rather common storm event (3-5-year return period) in 2009 on the Island of Hawaii. The opposite trend behavior in extreme events is observed on Oahu and Maui, where rainfall extremes have become less frequent in the last five decades. A positive relationship is found between the precipitation extremes and Southern Oscillation Index ( SOI), implying greater extreme events during La Niña years and the opposite for El Niño years. [ABSTRACT FROM AUTHOR]

ABSTRACT Hailstorms have become a serious meteorological risk in mid-latitude countries because of their small-scale development and short time span, and their forecasting remains problematic. Moreover, the lack of reliable hailstorm databases is an important handicap for Numerical Weather Prediction (NWP) model validation, time trend studies and establishment of hailstorm relationships with global warming and climate change. However, this can be overcome by ascertaining physical relationships between favourable synoptic patterns and mesoscale trigger factors for hailstorm development in a local study area. North-eastern Spain is one of the European regions with largest number of hailstorm days ( HD) observed in the summer. Since 2001, from May through September, reliable databases of hailstorm occurrence in the middle Ebro Valley have been constructed, which include intensity, temporal frequency and spatial coordinate data. June and July 2006 had the largest number of HD in 2001-2010. With the objective of analysing meteorological factors responsible for this anomaly, atmospheric patterns at low and mid-tropospheric levels were studied. We determined a set of special synoptic configurations, with an evident deviation from climatic values generating anomalies of 850 hPa temperature relative to the characteristic values of 2001-2010 and 1950-2010. An analysis of these anomalies detected a positive trend of 850 hPa temperature and geopotential height in the western Mediterranean area. As a consequence, the characteristic synoptic circulation has changed since 1950, towards low-level patterns favouring adequate thermodynamic environments for hailstorm development in north-eastern Spain. Finally, after a cluster analysis, we studied periodicities in the monthly 850 hPa temperature field to improve knowledge for seasonal forecasting of hailstorms. [ABSTRACT FROM AUTHOR]

ABSTRACT A workshop was held at the University of the West Indies, Jamaica, in May 2012 to build capacity in climate data rescue and to enhance knowledge about climate change in the Caribbean region. Scientists brought their daily observational surface temperature and precipitation data from weather stations for an assessment of quality and homogeneity and for the calculation of climate indices helpful for studying climate change in their region. This study presents the trends in daily and extreme temperature and precipitation indices in the Caribbean region for records spanning the 1961-2010 and 1986-2010 intervals. Overall, the results show a warming of the surface air temperature at land stations. In general, the indices based on minimum temperature show stronger warming trends than indices calculated from maximum temperature. The frequency of warm days, warm nights and extreme high temperatures has increased while fewer cool days, cool nights and extreme low temperatures were found for both periods. Changes in precipitation indices are less consistent and the trends are generally weak. Small positive trends were found in annual total precipitation, daily intensity, maximum number of consecutive dry days and heavy rainfall events particularly during the period 1986-2010. Correlations between indices and the Atlantic multidecadal oscillation ( AMO) index suggest that temperature variability and, to a lesser extent, precipitation extremes are related to the AMO signal of the North Atlantic surface sea temperatures: stronger associations are found in August and September for the temperature indices and in June and October for some of the precipitation indices. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents an analysis of observed climate extremes over the Arabian Peninsula ( AP); a region for which little such analysis has been available. A set of climate extremes indices developed by the Expert Team on Climate Change Detection and Indices ( ETCCDI) were computed and analysed for trends including the periods 1970-2008 and 1986-2008 at 23 stations covering six countries (Bahrain, Qatar, Kuwait, Oman, Saudi Arabia and UAE) and for Bahrain (1950-2008), Kuwait (1962-2008), Masirah and Salalah (1943-2008). The results indicate a general decreasing trend of cold temperature extremes and increasing trends of the warm temperature extremes during the periods of analysis. Over the whole region, a remarkable and highly significant increase in very warm nights during 1986-2008 has occurred. In general higher temperature trends (magnitudes/significance) are reported over the northern AP in the day-time extremes while for the night-time extremes the trends are higher and significant for the southern region especially during the recent decades. The precipitation indices trends are weak and insignificant except for the annual count of days when precipitation exceeds 10 mm which shows a significant decrease during 1986-2008. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article we examine trends in rainfall in the Fiji, using records from 14 stations in Fiji. These records cover more stations and significantly longer periods (>90 years for several stations) than those used in any previous studies. We find that over a period of nearly 100 years there is high interannual variability but no significant long-term trend in annual rainfall in Fiji in either 'wet-side' or 'dry-side' stations. This result is consistent with the more restricted results of almost all previous studies. We also find no significant trends in 'wet season' and 'dry season' rainfall, considered separately. Thus unlike temperature data, rainfall data from Fiji provides little evidence of long-term climate change. There is an indication that the few dry seasons with rainfall more than one standard deviation below the mean have occurred more frequently in the most recent 50 years than in the previous 50. Our results confirm that there is a significant influence of the El Niño Southern Oscillation on rainfall in Fiji, especially on the 'dry' side of the larger islands. However, we find that the Interdecadal Pacific Oscillation (IPO) does not modulate the correlation between rainfall in Fiji and the Southern Oscillation Index; contrary to the case in eastern Australia, this correlation is strongly positive for all phases of the IPO. [ABSTRACT FROM AUTHOR]

An analysis of recent-past changes in rainfall records from the three major transnational basins in Iberia was performed, using data from Spain and Portugal which are generally considered separately. Change point (to detect abrupt changes in rainfall) and trend analysis were performed in the basins of rivers Douro, Tagus and Guadiana for the period 1961 to 2009. Nonparametric tests (Pettitt, cusum and Mann-Kendall) were used in order not to assume a specific distribution for the data. Field significance was taken into account when applying the tests for trends and change points. The importance of spatial correlation when calculating field significance was demonstrated. As well as finding changes in rainfall which have great significance for water resources, some important issues are raised as to the nature of changes in rainfall to be expected. Significant decreases in rainfall were found for the month of February and, to a lesser extent, March. Significant increases in rainfall were found for October in the Spanish side of Douro and Tagus catchments. The variability of the NAO index was considered a likely explanation for the changes detected. It was also demonstrated that changes in rainfall cannot be interpreted as trends or change points always because the pattern of change can be more complex than these two simplistic ways of describing change. Furthermore, the magnitude of the change can be completely different depending on the type of change assumed. Therefore the quantification of the change must be made with care, as the widely used linear trend can result in an overestimation of the change and, in principle, is not coherent with the multiple alternative hypotheses (different admissible monotonic patterns) implied by the Mann-Kendall test. Copyright © 2013 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

This study analyses observed and projected climatic trends over Ethiopia, through analysis of temperature and rainfall records and related meteorological fields. The observed datasets include gridded station records and reanalysis products; while projected trends are analysed from coupled model simulations drawn from the IPCC 4th Assessment. Upward trends in air temperature of + 0.03 °C year−1 and downward trends in rainfall of − 0.4 mm month−1 year−1 have been observed over Ethiopia's southwestern region in the period 1948-2006. These trends are projected to continue to 2050 according to the Geophysical Fluid Dynamics Lab model using the A1B scenario. Large scale forcing derives from the West Indian Ocean where significant warming and increased rainfall are found. Anticyclonic circulations have strengthened over northern and southern Africa, limiting moisture transport from the Gulf of Guinea and Congo. Changes in the regional Walker and Hadley circulations modulate the observed and projected climatic trends. Comparing past and future patterns, the key features spread westward from Ethiopia across the Sahel and serve as an early warning of potential impacts. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

A data set of observed fire weather in Australia from 1973-2010 is analysed for trends using the McArthur Forest Fire Danger Index (FFDI). Annual cumulative FFDI, which integrates daily fire weather across the year, increased significantly at 16 of 38 stations. Annual 90th percentile FFDI increased significantly at 24 stations over the same period. None of the stations examined recorded a significant decrease in FFDI. There is an overall bias in the number of significant increases towards the southeast of the continent, while the largest trends occur in the interior of the continent and the smallest occur near the coast. The largest increases in seasonal FFDI occurred during spring and autumn, although with different spatial patterns, while summer recorded the fewest significant trends. These trends suggest increased fire weather conditions at many locations across Australia, due to both increased magnitude of FFDI and a lengthened fire season. Although these trends are consistent with projected impacts of climate change on FFDI, this study cannot separate the influence of climate change, if any, with that of natural variability. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Research has found that both flood magnitude and frequency in the UK may have increased over the last five decades. However, evaluating whether or not this is a systematic trend is difficult because of the lack of longer records. Here we compile and consider an extreme flood record that extends back to 1770. Since 1770, there have been 137 recorded extreme floods. However, over this period, there is not a unidirectional trend of rising extreme flood risk over time. Instead, there are clear flood-rich and flood-poor periods. Three main flood-rich periods were identified: 1873-1904, 1923-1933, and 1994 onwards. To provide a first analysis of what is driving these periods, and given the paucity of more sophisticated datasets that extend back to the 18th century, objective Lamb weather types were used. Of the 27 objective Lamb weather types, only 11 could be associated with the extreme floods during the gauged period, and only 5 of these accounted for > 80% of recorded extreme floods The importance of these five weather types over a longer timescale for flood risk in Carlisle was assessed, through calculating the proportion of each hydrological year classified as being associated with these flood-generating weather types. Two periods clearly had more than the average proportions of the year classified as one of the flood causing weather types; 1900-1940 and 1983-2007; and these two periods both contained flood-rich hydrological records. Thus, the analysis suggests that systematic organisation of the North Atlantic climate system may be manifest as periods of elevated and reduced flood risk, an observation that has major implications for analyses that assume that climatic drivers of flood risk can be either statistically stationary or are following a simple trend. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]