Analysis of Temperature Extremes over India Using Sheffield & IMD Dataset

Temperature extremes significantly contribute to climate change; therefore, the analysis of temperature extremes is essential in detecting and attributing climate change. The present study aims to analyze the spatiotemporal variations in the temperature extremes over India, using 0.25° × 0.25° high-resolution Sheffield temperature gridded dataset for a period of 62 years (1951–2012). In addition, the spatial distribution, statistical relation and trend pattern of Sheffield’s temperature dataset is compared with 1°×1°, gridded temperature dataset of Indian Meteorological Department (IMD). The mean of temperature indices show nearly similar spatial distribution in both datasets; however trend pattern of extreme indices show significant differences over different homogeneous temperature regions of India. There is mostly disagreement between the two datasets, for trend patterns of extreme indices at different homogeneous regions, but few grids show reasonable agreement for similar trend pattern. Both datasets reported a significant decreasing trend in TX10p (amount of cool days) and TN10p (amount of cold nights) at maximum grids for the 1951–2012 period. In addition, a significant increasing trend in TX90p (amount of hot days) and WSDI (warm spell duration indicator) at maximum grids during post-1981 and 1951–2012 is observed in both datasets. A comprehensive insight into different characteristics (spatial distribution, statistical relation and trend patterns) of Sheffield’s temperature dataset will help in understanding the applicability of Sheffield temperature dataset for climate modeling and prediction studies over India.

Eucalyptus Obliqua Tall Forest in Cool, Temperate Tasmania Becomes a Carbon Source during a Protracted Warm Spell in November 2017

Tasmania, which has a cool temperate climate, experienced a protracted warm spell in November 2017. In absolute terms, temperatures during the warm spell were lower than those usually characterising heatwaves. Nonetheless the November 2017 warm spell represented an extreme anomaly based on the local historical climate. Eddy covariance measurements of fluxes made in a Eucalyptus obliqua tall forest at Warra, southern Tasmania, recorded a 39% reduction in gross primary productivity (GPP) during the warm spell. A coincident increase in ecosystem respiration during the warm spell resulted in the forest switching from a carbon sink to a source. Net radiation was significantly higher during the warm spell than in the same period in the preceding two years. This additional radiation drove an increase in latent heat but not sensible heat. Stomatal regulation to limit water loss was unlikely based on soil moisture and vapour pressure deficits. Temperatures during the warm spell were supra-optimal for GPP at that site for 75% of the daylight hours. The decline in GPP during the warm spell was therefore most likely due to temperatures exceeding the site optimum for GPP. These forests will be weaker carbon sinks if, as predicted, heatwave events become more common.

Current and Predicted Future Winter Warm Spells Would Affect Douglas Fir (Pseudotsuga menziesii (Mirb.), Franco) Seeds in the Early Stage of Germination More Than in the Late Stage of Germination

Most tree species in the temperate climatic zone (including Douglas fir) disperse seeds in autumn. Some of them must be exposed to cold (0–10 °C) and moist conditions (cold stratification) to overcome dormancy and trigger germination. In the Northern Hemisphere, winter warm spells occur more frequently and last longer than in recent decades from eastern Canada to Europe. Our main research objective was to investigate the influence of current (1 or 3 days at day/night temperatures: 15 °C/10 °C) and future predicted (5 days at day/night temperatures: 25 °C/15 °C) winter warm spells on dormancy breaking and germination traits (germination energy—GE; germination capacity—GC; final germination capacity—FGC) of Douglas fir seeds from four old-growth stands in northern Poland. For this purpose, we interrupted cold stratification of seeds at different time points, i.e., after 3 weeks; 6 weeks; 9 or 3 weeks and 6 weeks; 3 and 9 weeks; 6 and 9 weeks; 3 and 6 weeks and 9 weeks. We found that for GE and GC, all main effects (populations—P; days of warm spell—D; stratification duration—W) and interactions were significant (except interaction P×D). FGC was significantly affected by the effects P and D and interactions of D × W and P × D × W. In addition, we found that the predicted warm spells negatively affected the early germination stage (GE and GC) of Douglas fir, but both current and future predicted winter conditions will not negatively affect the late germination stage (FGC).

Do Extreme Climate Events Cause the Degradation of Malus sieversii Forests in China?

Frequent extreme climate events have attracted considerable attention around the world. Malus sieversii in Xinjiang is the ancestor of cultivated apple, and it is mainly distributed in the Ili river valley at end of the Tianshan Mountains. Wild fruit forests have been degraded, but the cause remains unclear. In order to identify whether extreme climate events caused this degradation reanalysis data and atmospheric circulation indices were used to determine the trends and the reasons for extreme climate changes. Subsequently, we further investigated the effect of extreme climate events on wild fruit forest using characteristics of extreme climate indices and tree-ring chronology. We found increasing trends in both extreme precipitation and warm indices, and decreasing trends in cool indices. Extreme climate events were mainly associated with the Atlantic Multidecadal Oscillation (AMO). Analysis of data of wind and geopotential height field at 500 hPa showed that strengthening wind, increasing geopotential height, cyclone and anti-cyclone circulation drivers contributed to extreme climate events. In the non-degraded region, there were significant positive correlations between tree-ring chronology and both extreme precipitation and extreme warm indices (except for warm spell duration indicator). The other extreme indices (except for heavy rain days) had a large correlation range with tree-rings in a 4–8-year period. These results indicated that extreme precipitation and extreme warm indices intensified M. sieversii growth of the non-degraded region on multi-time scales. In contrast, the degraded region showed insignificant negative relationship between tree-ring chronology and both extreme precipitation and extreme warm indices [except for warm spell duration index (WSDI)], and significant negative correlations in a 4–8-year period were detected between tree-ring chronology and most of the extreme precipitation indices, including heavy rain days, very wet days, cold spell duration indicator, simple precipitation intensity index (SDII), and annual total precipitation. Under the long disturbance of inappropriate anthropic activities, extreme climate has caused the outbreak of pests and diseases resulting in the degeneration of wild fruit forest. Our study provides scientific guidance for the ecosystem conservation in wild fruit forest in China, and also across the region.

Extreme climate response to marine cloud brightening in the arid Sahara-Sahel-Arabian Peninsula zone

Purpose Climatic extreme events are predicted to occur more frequently and intensely and will significantly threat the living of residents in arid and semi-arid regions. Therefore, this study aims to assess climatic extremes’ response to the emerging climate change mitigation strategy using a marine cloud brightening (MCB) scheme. Design/methodology/approach Based on Hadley Centre Global Environmental Model version 2-Earth System model simulations of a MCB scheme, this study used six climatic extreme indices [i.e. the hottest days (TXx), the coolest nights (TNn), the warm spell duration (WSDI), the cold spell duration (CSDI), the consecutive dry days (CDD) and wettest consecutive five days (RX5day)] to analyze spatiotemporal evolution of climate extreme events in the arid Sahara-Sahel-Arabian Peninsula Zone with and without MCB implementation. Findings Compared with a Representative Concentration Pathways 4.5 scenario, from 2030 to 2059, implementation of MCB is predicted to decrease the mean annual TXx and TNn indices by 0.4–1.7 and 0.3–2.1°C, respectively, for most of the Sahara-Sahel-Arabian Peninsula zone. It would also shorten the mean annual WSDI index by 118–183 days and the mean annual CSDI index by only 1–3 days, especially in the southern Sahara-Sahel-Arabian Peninsula zone. In terms of extreme precipitation, MCB could also decrease the mean annual CDD index by 5–25 days in the whole Sahara and Sahel belt and increase the mean annual RX5day index by approximately 10 mm in the east part of the Sahel belt during 2030–2059. Originality/value The results provide the first insights into the impacts of MCB on extreme climate in the arid Sahara-Sahel-Arabian Peninsula zone.

Trends in Winter Warm Spells in the Central England Temperature Record

An important impact of climate change on agriculture and the sustainability of ecosystems is the increase of extended warm spells during winter. We apply crossing theory to the central England temperature time series of winter daily maximum temperatures to quantify how increased occurrence of higher temperatures translates into more frequent, longer-lasting, and more intense winter warm spells. We find since the late 1800s an overall two- to threefold increase in the frequency and duration of winter warm spells. A winter warm spell of 5 days in duration with daytime maxima above 13°C has a return period that was often over 5 years but now is consistently below 4 years. Weeklong warm intervals that return on average every 5 years now consistently exceed ~13°C. The observed changes in the temporal pattern of environmental variability will affect the phenology of ecological processes and the structure and functioning of ecosystems.

Changes in temperature and heat waves over Africa using observational and reanalysis datasets

<p>Aiming to provide comprehensive information for climate change at regional level, we assess temperature and heat waves and their spatiotemporal trend and time of emergence over different regions of the African continent.  We analyze observational data of Climate Research Unit Time Series version 4.03 (CRU TS) and the three state-of-the-art reanalysis datasets; European Center for Medium-Range Weather Forecasts Reanalysis 5 (ERA5), National Oceanic Atmospheric Administration’s Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2) and the Japanese Meteorological Agency’s 55 years reanalysis (JRA-55). We assess changes in monthly mean temperature and the agreement between observations and reanalyses. Changes in heat waves are analyzed based on reanalysis datasets because of their high temporal resolution. Heat waves are defined using absolute and relative thresholds, the number of summer days, tropical nights, the percentage of days with maximum and mean temperature above the 90<sup>th</sup> percentile, the warm nights and the warm spell duration index.  The results show increasing trends in monthly mean temperature in all four regions of Africa with different rate of change. A statistically significant trends in heat waves is found in all the regions.  Years of highest heat wave occurrence are identified in 2010 for Northern and Western Africa and 2016 for Eastern and Southern Africa. Minimum-temperature based indices, tropical nights and warm nights, show the highest increase in decadal trends and earliest time of emergence, respectively.</p><p><strong>Key words:</strong> climate change; temperature; heat waves; time of emergence; reanalysis; Africa</p>

Analysis of Temperature and Precipitation Trends Observed at Some Selected Districts of Punjab, Pakistan

Present study examines the trends of extreme daily temperature and rainfall indices in some selectedmeteorological stations/districts of the Punjab. Due to paucity of data only six weather stations were selected from thewhole Punjab, having data of 33 years for temperature and precipitation on daily basis. A set of 14 indices(recommended by climate ET) were used to calculate the trends over a period of 32 years (1985–2017) by usingRClimDex (1.0) software package. These results showed that the number of tropical nights (TR20) and warm nights(TN90p) has been increasing in selected weather stations/districts and number for cool nights (TN10p) has been falling.Other temperature related indices trends such as, summer days, warms days, warm spell duration indicator (WSDI) andcool spell duration (CSDI) shows a mix pattern. The precipitation indices like SDII, RX1day, R10mm and PRCPTOTshowed an increasing trend in some selected stations. Most of the trends were not significant at level of 0.05 % whilemaximum day temperature increase has been observed at five out of six selected stations. Similarly, an average increasein precipitation in the vicinity of 3 mm per decade has been noted. The annual total rainfall and number of heavyrainfall days has also increased by 18 mm and 8.4 mm respectively during each decade. The analysis identified andhighlighted a slight change which was not temporally and spatially rational. However, there is need to more andadequate yearly data of different weather stations across the Punjab to identify the ongoing apparent and impeccablechanges in climate of the Punjab province.

Analysis of Temperature and Precipitation Trends Observed at Some Selected Districts of Punjab, Pakistan

Present study examines the trends of extreme daily temperature and rainfall indices in some selectedmeteorological stations/districts of the Punjab. Due to paucity of data only six weather stations were selected from thewhole Punjab, having data of 33 years for temperature and precipitation on daily basis. A set of 14 indices(recommended by climate ET) were used to calculate the trends over a period of 32 years (1985–2017) by usingRClimDex (1.0) software package. These results showed that the number of tropical nights (TR20) and warm nights(TN90p) has been increasing in selected weather stations/districts and number for cool nights (TN10p) has been falling.Other temperature related indices trends such as, summer days, warms days, warm spell duration indicator (WSDI) andcool spell duration (CSDI) shows a mix pattern. The precipitation indices like SDII, RX1day, R10mm and PRCPTOTshowed an increasing trend in some selected stations. Most of the trends were not significant at level of 0.05 % whilemaximum day temperature increase has been observed at five out of six selected stations. Similarly, an average increasein precipitation in the vicinity of 3 mm per decade has been noted. The annual total rainfall and number of heavyrainfall days has also increased by 18 mm and 8.4 mm respectively during each decade. The analysis identified andhighlighted a slight change which was not temporally and spatially rational. However, there is need to more andadequate yearly data of different weather stations across the Punjab to identify the ongoing apparent and impeccablechanges in climate of the Punjab province.