Gaston R. Demarée

Trends of Extreme Temperatures in Europe and China Based on Daily Observations

Ten of the longest daily temperature series presently available in Europe and China are analysed, focusing on changes in extremes since pre-industrial times. We consider extremes in both a relative (with respect to the time of year) and an absolute sense. To distinguish changes in extremes from changes affecting the main part of the temperature distribution, a percentile smaller than 10 (and/or larger than 90) is recommended for defining an extreme. Three periods of changes in temperature extremes are identified: decreasing warm extremes before the late 19th century; decreasing cold extremes since then and increasing warm extremes since the 1960s. The early decreases and recent increases of warm extremes dominate in summer, while the decrease of cold extremes for winter persists throughout the whole period. There were more frequent combined (warm plus cold) extremes during the 18th century and the recent warming period since 1961 at most of the ten stations, especially for summer. Since 1961, the annual frequency of cold extremes has decreased by about 7% per century with warm extremes increasing by more than 10% per century but with large spatial variability. Compared with recent annual mean warming of about 2–3 ° C/century, the coldest winter temperatures have increased atthree times this rate, causing a reduced within-season range and therefore less variable winters. Changes in the warmest summer temperatures since 1961 exhibit large spatial variability, with rates of change ranging from slightly negative to 6 ° C/century. More extensive station observations since 1961 indicate that the single site results are representative of larger regions, implying also that the extremes studied are the result of large-scale changes. Recent circulation changes in daily gridded pressure data, used as an indicator of wind speed changes, support the results by explaining some of the trends.

Long-term (105 years) variability in rain erosivity as derived from 10-min rainfall depth data for Ukkel (Brussels, Belgium): Implications for assessing soil erosion rates

intensity–kinetic energy equation (I-KE) for central Belgium. This R value is 26% larger compared to the R factor based on the I-KE equation recommended in the RUSLE. No significant monotonic trend in annual R factor could be observed over the entire period, yet a standard normal homogeneity test showed a significantly higher R factor (+31%) for the period 1991–2002 compared to the period 1898–1990. Annual variability in R factor is very high, with a coefficient of variance of 31%. For central Belgium, rain erosivity is highest in the period May–September, which corresponds well with observed soil loss rates and the occurrence of muddy floods. Especially the period May–June is critical with respect to soil erosion. The year-to-year variability in rain erosivity for May–June shows a different temporal pattern than the annual erosivity. No statistically significant increase in rain erosivity for May–June was found, and during the last decade of the twentieth century these values are lower than average. Despite the lack of a significant trend in annual rain erosivity, average 10-year erosion rates calculated with the RUSLE have increased by 24–34% from 1903–1912 to 1993–2002 for major crops grown in central Belgium, solely as a consequence of changing rain erosivity through time.

An indication of climatic change as seen from the rainfall data of a mauritanian station

SummaryDaily precipitation amounts from the meteorological station at Kaédi (Mauritania) are available since 1904, the countrys longest record. The series constitutes an excellent tool for studying variations in the precipitation climate. Analysis of the annual precipitation amounts reveals the existence of a statistically highly significant downward trend which started in the sixties and is still continuing at present.It was further found that the entire reference period 1904–1988 needs, for reasons of data stationarity, to be split into two parts, corresponding respectively to the periods 1904–1967 and 1968–1988, the year 1967 being estimated as the change-point. The latter period corresponds to the “drought” which has prevailed over the Sahel region since 1968. The jump disclosed in the hydroclimatic system is indicative of the existence of multiple stable climate regimes.

Effects of Historical Urbanization in the Brussels Capital Region on Surface Air Temperature Time Series: A Model Study

Abstract The authors examine the local impact of change in impervious surfaces in the Brussels capital region (BCR), Belgium, on trends in maximum, minimum, and mean temperatures between 1960 and 1999. Specifically, data are combined from remote sensing imagery and a land surface model including state-of-the-art urban parameterization—the Town Energy Balance scheme. To (i) isolate effects of urban growth on near-surface temperature independent of atmospheric circulations and (ii) be able to run the model over a very long period without any computational cost restrictions, the land surface model is run in a stand-alone mode coupled to downscaled 40-yr ECMWF reanalysis data. BCR was considered a lumped urban volume and the rate of urbanization was assessed by estimating the percentage of impervious surfaces from Landsat images acquired for various years. Model simulations show that (i) the annual mean urban bias (AMUB) on minimum temperature is rising at a higher rate (almost 3 times more) than on maximum t...

Current status and predicted impact of climate change on forest production and biogeochemistry in the temperate oceanic European zone: review and prospects for Belgium as a case study

Reviews of the current statuses of forests and the impacts of climate change on forests exist at the (sub)continental scale, but rarely at country and regional levels, meaning that information on causal factors, their impacts, and specific regional properties is often inconsistent and lacking in depth. Here, we present the current status of forest production and biogeochemistry and the expected impacts of climate change on them for Belgium. This work represents a case study for the temperate oceanic zone, the most important bioclimatic zone in northwestern Europe. Results show that Belgian forests are mainly young, very productive, and have a high C-sequestration capacity. Major negative anomalies in tree vitality were observed in the 1990s and—as result of disturbances—in the last decade for sensitive species as poplars and European beech. The most severe disturbances were caused by extreme climatic events, directly (e.g. storms) or indirectly (e.g. insect outbreaks after a mild autumn with an early/severe frost). Because of atmospheric deposition and soil fertilization (due to the previous use of the land), nutrient stocks of Belgian forests are likely to sustain the future enhancement in productivity which is expected to follow the increase in atmospheric CO2 concentration that will occur in years to come. However, in the long term, such (enhanced) forest production is likely to be limited by nutrient deficiencies at poor sites and by drought for sensitive species such as beech and (particularly) Norway spruce. Drought conditions will likely increase in the future, but adverse effects are expected on a relatively limited number of tree species. The potential impacts of windstorms, insects and fungi should be carefully investigated, whereas fires are less of a concern.

Origins of the Word “Phenology”

Observing and documenting life cycle stages of plants and animals have been tradition and necessity for humans throughout history. Phenological observations—as called by their modern scientific name—were key to successful hunting and farming because the precise knowledge of animal behavior and plant growth, as well as their timing with changing seasons, was critical for survival. In todays context of environmental awareness and climate change research, phenological observations have become prime indicators of documenting altered life cycles due to environmental change in disciplines from biology to climatology, geography, and environmental history. Observations on the ground, from space, and from models of different complexity describe intra-annual and interannual changes of life cycles at individual, pixel, or grid box scale.

Grubbs revisited: a statistical technique to differentiate measurement methods of the degree of exposure of raingauges in a network

Abstract Precipitation measurement by raingauges is biased by the systematic error resulting from deformation of the local wind field due to the presence of the gauge itself. To correct for this error, it is necessary to know the degree of site exposure. Four measurement methods are dealt with to determine site exposure. It is shown how statistical techniques developed by Grubbs can be used to select the most precise measurement method.

An Indication of an Abrupt Climatic Change as Seen from the Rainfall Data of a Mauritanian Station

This paper demonstrates the view that the Sahelian precipitation climate can be seen as an aperiodic but recurrent phenomenon alternating between two or more steady climate states. An “abrupt” climatic change is assessed through non-parametrical statistical tests applied to the annual, seasonal and monthly long-term precipitation time series of a Mauritanian station.

The 1780s: Global Climate Anomalies, Floods, Droughts, and Famines

This handbook offers the first comprehensive, state-of-the-field guide to past weather and climate and their role in human societies. Bringing together dozens of international specialists from the sciences and humanities, this volume describes the methods, sources, and major findings of historical climate reconstruction and impact research. Its chapters take the reader through each key source of past climate and weather information and each technique of analysis; through each historical period and region of the world; through the major topics of climate and history and core case studies; and finally through the history of climate ideas and science. Using clear, non-technical language, The Palgrave Handbook of Climate History serves as a textbook for students, a reference guide for specialists and an introduction to climate history for scholars and interested readers.

Historical records of earthquakes for Greenland and Labrador in Moravian Missionary journals

In the general seismological literature, there is scant information regarding historical earthquakes in Greenland and Labrador. This paper seeks to redress this by focusing on earthquakes during the eighteenth and nineteenth centuries (to the early 1870s) in western Greenland and Labrador, regions bordering Davis Strait. The information is drawn primarily from the journals of Danish and Moravian missionaries and missionary newspapers. The missionaries were keen observers of nature and natural phenomena, and their records constitute a reliable source of climatic and environmental information.