A suite of climate change indices derived from daily temperature and precipitation data, with a primary focus on extreme events, were computed and analyzed. By setting an exact formula for each index and using specially designed software, analyses done in different countries have been combined seamlessly. This has enabled the presentation of the most up-to-date and comprehensive global picture of trends in extreme temperature and precipitation indices using results from a number of workshops held in data-sparse regions and high-quality station data supplied by numerous scientists world wide. Seasonal and annual indices for the period 1951-2003 were gridded. Trends in the gridded fields were computed and tested for statistical significance. Results showed widespread significant changes in temperature extremes associated with warming, especially for those indices derived from daily minimum temperature. Over 70% of the global land area sampled showed a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights. Some regions experienced a more than doubling of these indices. This implies a positive shift in the distribution of daily minimum temperature throughout the globe. Daily maximum temperature indices showed similar changes but with smaller magnitudes. Precipitation changes showed a widespread and significant increase, but the changes are much less spatially coherent compared with temperature change. Probability distributions of indices derived from approximately 200 temperature and 600 precipitation stations, with near-complete data for 1901-2003 and covering a very large region of the Northern Hemisphere midlatitudes (and parts of Australia for precipitation) were analyzed for the periods 1901-1950, 1951-1978 and 1979-2003. Results indicate a significant warming throughout the 20th century. Differences in temperature indices distributions are particularly pronounced between the most recent two periods and for those indices related to minimum temperature. An analysis of those indices for which seasonal time series are available shows that these changes occur for all seasons although they are generally least pronounced for September to November. Precipitation indices show a tendency toward wetter conditions throughout the 20th century.

/pdf/global-observed-changes-in-daily-climate-extremes-of-50pijshpdk.pdf

Global observed changes in daily climate extremes of temperature and precipitation

/pdf/observations-surface-and-atmospheric-climate-change-2q0n23ht4i.pdf

Observations: Surface and Atmospheric Climate Change

http://www.hydrology.bee.cornell.edu/BEE3710Handouts/HuntingtonJHYDRO06.pdf

Evidence for intensification of the global water cycle: Review and synthesis

A new global dataset of derived indicators has been compiled to clarify whether fre- quency and/or severity of climatic extremes changed during the second half of the 20th century. This period provides the best spatial coverage of homogenous daily series, which can be used for calcu- lating the proportion of global land area exhibiting a significant change in extreme or severe weather. The authors chose 10 indicators of extreme climatic events, defined from a larger selection, that could be applied to a large variety of climates. It was assumed that data producers were more inclined to release derived data in the form of annual indicator time series than releasing their origi- nal daily observations. The indicators are based on daily maximum and minimum temperature series, as well as daily totals of precipitation, and represent changes in all seasons of the year. Only time series which had 40 yr or more of almost complete records were used. A total of about 3000 indicator time series were extracted from national climate archives and collated into the unique dataset described here. Global maps showing significant changes from one multi-decadal period to another during the interval from 1946 to 1999 were produced. Coherent spatial patterns of statistically signif- icant changes emerge, particularly an increase in warm summer nights, a decrease in the number of frost days and a decrease in intra-annual extreme temperature range. All but one of the temperature- based indicators show a significant change. Indicators based on daily precipitation data show more mixed patterns of change but significant increases have been seen in the extreme amount derived from wet spells and number of heavy rainfall events. We can conclude that a significant proportion of the global land area was increasingly affected by a significant change in climatic extremes during the second half of the 20th century. These clear signs of change are very robust; however, large areas are still not represented, especially Africa and South America.

/pdf/observed-coherent-changes-in-climatic-extremes-during-the-3smwacuu22.pdf

Observed coherent changes in climatic extremes during the second half of the twentieth century

Changes in climate extremes and their impacts on the natural physical environment: An overview of the IPCC SREX report

Trends in Canadian temperature and precipitation during the 20th century are analyzed using recently updated and adjusted station data. Six elements, maximum, minimum and mean temperatures along with diurnal temperature range (DTR), precipitation totals and ratio of snowfall to total precipitation are investigated. Anomalies from the 1961–1990 reference period were first obtained at individual stations, and were then used to generate gridded datasets for subsequent trend analyses. Trends were computed for 1900–1998 for southern Canada (south of 60°N), and separately for 1950–1998 for the entire country, due to insufficient data in the high arctic prior to the 1950s. From 1900–1998, the annual mean temperature has increased between 0.5 and 1.5°C in the south. The warming is greater in minimum temperature than in maximum temperature in the first half of the century, resulting in a decrease of DTR. The greatest warming occurred in the west, with statistically significant increases mostly seen during...

Temperature and precipitation trends in Canada during the 20th century

This study presents trends computed for the past 30–50 years for 11 hydroclimatic variables obtained from the recently created Canadian Reference Hydrometrie Basin Network database. It was found that annual mean streamflow has generally decreased during the periods, with significant decreases detected in the southern part of the country. Monthly mean streamflow for most months also decreased, with the greatest decreases occurring in August and September. The exceptions are March and April, when significant increases in streamflow were observed. Significant increases were identified in lower percentiles of the daily streamflow frequency distribution over northern British Columbia and the Yukon Territory. In southern Canada, significant decreases were observed in all percentiles of the daily streamflow distribution. Breakup of river ice and the ensuing spring freshet occur significantly earlier, especially in British Columbia. There is also evidence to suggest earlier freeze-up of rivers, particularly in eastern Canada. The trends observed in hydroclimatic variables are entirely consistent with those identified in climatic variables in other Canadian studies.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000WR900357

Trends in Canadian streamflow

Recent studies have shown that, since 1900, mean annual temperature over southern Canada has increased by an average of 0.98C, with the largest warming during winter and early spring. Every season was associated with greater increases in minimum temperature as opposed to maximum, thus resulting in a significant decrease in the daily temperature range (DTR). The second half of the twentieth century was associated with significant winter and spring warming in the south and west, and cooling in the northeast. However, no significant changes in DTR were observed during this period. This investigation goes beyond the annual/seasonal scales by examining trends and variability in daily minimum and maximum temperature with particular emphasis on extremes. Using recently updated, homogenized daily data, spatial and temporal characteristics of daily and extreme temperaturerelated variables are analyzed on a seasonal basis for the periods of 1900‐98 (southern Canada), and 1950‐98 (the entire country). From 1900 to 1998, the majority of southern Canada shows significantly increasing trends to the lower and higher percentiles of the daily minimum and maximum temperature distribution. The findings translate into fewer days with extreme low temperature during winter, spring, and summer and more days with extreme high temperature during winter and spring. No consistent trends are found for the higher percentiles of summer daily maximum temperature, indicating little change to the number of extreme hot summer days. Over the southwest, increases are larger to the left-hand side of the daily minimum and maximum temperature distribution, resulting in significant decreases to the intraseasonal standard deviation of daily temperature. The 1950‐98 results are somewhat different from the entire century, especially, during winter and spring. This result includes significant increases to the low and high percentiles over the west, and decreases over the east. This analysis reveals that the largest individual daily temperature trends (both minimum and maximum) occur during winter and early spring, when substantial warming is observed. For summer, increases are only associated with daily minimum temperature. Autumn displays varying results, with some late season cooling, mainly over western regions. The observed warming trends have a substantial effect on several economically sensitive indices. This effect includes significant increases in the number of growing and cooling degree days and significant decreases in heating degree days. In addition, the length of the frost-free period is significantly longer over most of the country.

Characteristics of Daily and Extreme Temperatures over Canada

A method to homogenize daily maximum and minimum temperatures over Canada is presented. The procedure is based on previously defined monthly adjustments derived from step changes identified in annual Canadian temperature series. Daily temperatures are adjusted by incorporating a linear interpolation scheme that preserves these monthly adjustments. The temperature trends and variations present in the homogenized monthly and annual datasets are therefore preserved. Comparisons between unadjusted and adjusted daily temperatures at collocated sites show that the greatest impact of the adjustments is on the annual mean of the daily maximum and minimum temperatures with little effect on the standard deviation. The frequency and distribution of the extremes are much closer to those provided by the target observations after adjustments. Furthermore, the adjusted daily temperatures produced by this procedure greatly improve the spatial pattern of the observed twentieth century extreme temperature trends a...

Homogenization of Daily Temperatures over Canada

Spatial and temporal characteristics of heavy precipitation events over Canada (excluding the high Arctic) are examined for the period 1900–98. In southern Canada, about 71% of total precipitation comes from rainfall events. In northern Canada, more than 50% of total precipitation comes from snowfall events. Heavy rainfall and snowfall events are thus defined for each season and station separately by identifying a threshold value that is exceeded by an average of three events per year. Annual and seasonal time series of heavy event frequency are then obtained by counting the number of exceedances per year. Characteristics of the intensity of heavy precipitation events are investigated examining the 90th percentiles of daily precipitation, the annual maximum daily value, and the 20-yr return values. It was found that decadal variability is the dominant feature in both the frequency and the intensity of extreme precipitation events over the country. For the country as a whole, there appear to be no...

W. D. Hogg

Papers

Temperature and precipitation trends in Canada during the 20th century

Trends in Canadian streamflow

Characteristics of Daily and Extreme Temperatures over Canada

Homogenization of Daily Temperatures over Canada

Spatial and Temporal Characteristics of Heavy Precipitation Events over Canada