David Lister

A review of methods to calculate extreme wind speeds

Methods to calculate extreme wind speeds are described and reviewed, including ‘classical’ methods based on the generalized extreme value (GEV) distribution and the generalized Pareto distribution (GPD), and approaches designed specifically to deal with short data sets. The emphasis is very much on the needs of users who seek an accurate method to derive extreme wind speeds but are not fully conversant with up-to-date developments in this complex subject area. First, ‘standard’ methods are reviewed: annual maxima, independent storms, r-largest extremes with the GEV distribution, and peak-over-threshold extremes with the GPD. Techniques for calculating the distribution parameters and quantiles are described. There follows a discussion of the factors which must be considered in order to fulfil the criterion that the data should be independent and identically distributed, and in order to minimize standard errors. It is commonplace in studies of extreme wind speeds that the time series available for analysis are very short. Finally, therefore, the paper deals with techniques applicable to data sets as short as two years, including simulation modelling and methods based on the parameters of the parent distribution.

Temporal and spatial temperature variability and change over Spain during 1850–2005

We analyze temporal and spatial patterns of temperature change over Spain during the period 1850–2005, using daily maximum (T max), minimum (T min), and mean (T mean) temperatures from the 22 longe ...

Daily mean sea level pressure reconstructions for the European-North Atlantic region for the period 1850-2003

Abstract The development of a daily historical European–North Atlantic mean sea level pressure dataset (EMSLP) for 1850–2003 on a 5° latitude by longitude grid is described. This product was produced using 86 continental and island stations distributed over the region 25°–70°N, 70°W–50°E blended with marine data from the International Comprehensive Ocean–Atmosphere Data Set (ICOADS). The EMSLP fields for 1850–80 are based purely on the land station data and ship observations. From 1881, the blended land and marine fields are combined with already available daily Northern Hemisphere fields. Complete coverage is obtained by employing reduced space optimal interpolation. Squared correlations (r 2) indicate that EMSLP generally captures 80%–90% of daily variability represented in an existing historical mean sea level pressure product and over 90% in modern 40-yr European Centre for Medium-Range Weather Forecasts Re-Analyses (ERA-40) over most of the region. A lack of sufficient observations over Greenland and...

Monthly mean pressure reconstructions for Europe for the 1780–1995 period

Monthly grid-point pressure data are reconstructed from station records of pressure for Europe since 1780. The region encompasses 35-70°N to 30°W-40°E. The reconstructions are based on a principal components regression technique, which relates surface pressure patterns to those of the station pressure data. The relationships are derived over a calibration period (1936-1995) and the results tested with independent data (the verification period, 1881-1935). The reconstructions are of excellent quality, although this is slightly lower for regions with poor station coverage in the early years, particularly during the summer months. The reconstructions are compared with other monthly mean pressure maps produced by Lamb and Johnson (1966) for the years 1780-1872 and by Kington (1980, 1988) for 1781-1785. Both of these map series show systematic biases relative to the present reconstructions.

Future Climate Impact on the Productivity of Sugar Beet (Beta vulgaris L.) in Europe

The impact of future climate change on sugar beet yields is assessed over western Europe using future (2021–2050) climate scenario data from a General Circulation Model (GCM) and the Brooms Barn simulation model of rain-fed crop growth and yield. GCM output for the 1961–1990 period is first compared with observed climate data and shown to be reliable for regions west of 24° E. Comparisons east of this meridian were less reliable with this GCM (HadCM2) and so were omitted from simulations of crop yield. Climate change is expected to bring yield increases of around 1 t/ha of sugar in northern Europe with decreases of a similar magnitude in northern France, Belgium and west/central Poland, for the period 2021–2050. Averaged for the study area (weighted by current regional production), yields show no overall change due to changed climate. However, this figure masks significant increases in yield potential (due to accelerated growth in warmer springs) and in losses due to drought stress. Drought losses are predicted to approximately double in areas with an existing problem and to become a serious new problem in NE France and Belgium. Overall west and central Europe simulated average drought losses rise from 7% (1961–1990) to 18% (2021–2050). The annual variability of yield (as measured by the coefficient of variation) will increase by half, from 10% to 15% compared to 1961–1990, again with potentially serious consequences for the sugar industry. The importance of crop breeding for drought tolerance is further emphasised. These changes are independent of the 9% yield increase which we estimate, on the basis of work by Demmers-Derks et al. (1998), is the likely direct effect of the increase in atmospheric CO2 concentration by 2021–2050.

Climatic impact on the productivity of sugar beet in Europe, 1961–1995

A recent study showed that drought stress was the major factor causing yield loss of the sugar beet crop in the UK. That study has been extended here by modelling potential and rain-fed yields (1961–1995) for European areas where irrigation of sugar beet is uncommon. The inputs to this study are an improved crop growth model, the European monthly half-degree gridded meteorological data time series, and a map of soil texture and available water capacity in sugar beet growing regions. Model outputs were scaled using a ratio of national mean to experimental plot yields to reflect commercial performance of a hypothetical 1998 variety for all years. The model was run on daily weather data reconstructed from monthly values. Potential yields increased from north to south and from west to east due to increased radiation receipts. Drought losses were greatest in east Ukraine and southern Russia, at over 40% of potential yield (5 t ha−1). Losses were intermediate (15–30% or about 2 t ha−1) in central Ukraine, west Poland, east Germany and England (sandy soils) and lowest in NW Europe and west Ukraine. Increasing continentality decreases the number of rainy days per month during summer and the fraction of diffuse radiation; this reduces the radiation use efficiency by as much as 11%. Model output was also used to examine the efficiency of sugar beet production across Europe; at the extremes, NW European farmers deliver about 80% of the potential rain-fed yield while Polish farmers are only able to deliver 40%. This study demonstrates the importance of breeding for drought stress tolerance in Europe.

Riverflow reconstructions for 15 catchments over England and Wales and an assessment of hydrologic drought since 1865

Recent years have seen increased risks of water supply problems because of reduced rainfall in some seasons. Over England and Wales most riverflow records beign during the 1950s and 1960s. The short record length, therefore, makes assessment of the rarity of some flow flow sequences difficult. A means of extending riverflow records is to reconstruct them using a simple catchment model and the plentiful monthly rainfall totals available for England and Wales. Riverflow data on a monthly basis have been reconstructed for 15 catchments for the period since the 1860s. The reconstructions are produced with a regression-based catchment model that related lagged values of rainfall to runoff. The statistical nature of the model required that any reconstructions be assessed over an independent data period. All perform almost as well as during the calibaration periods. Using the reconstructions, recent hydrologic droughts are put into a longer term context. On one of the catchments is the most extreme 6 months (April-September) average riverflow found to occur during the 1986-1995 period. On a number of catchments, the extreme year is 1976 or 1984. Flows were low during 1989-1992 and 1995, with the former four year period being unusual, because the years occurred in succession. On all 15 catchments, however, an earlier sequence occurring between 1865 and 1980 is more severe.

The daily temperature record for St. Petersburg, 1743-1996

The derivation of the long daily temperature record from St. Petersburg is described. Some alterations in observation times, procedural changes and possible site moves are adjusted for, but correction for a probable urbanization influence of up to 1.0 °C over the 20th century is not attempted. The daily temperature series is then analysed for long-term changes in the numbers of daily extreme values. Although the 20th century shows a clear trend to lower numbers of extremely cold days, warm day counts indicate a much smaller change. The 1990s have been exceptionally warm but only just exceed some earlier decades such as the 1930s.

A Southeastern South American Daily Gridded Dataset of Observed Surface Minimum and Maximum Temperature for 1961–2000

This study presents a southeastern South American gridded dataset of daily minimum and maximum surface temperatures for 1961–2000. The data used for the gridding are observed daily data from meteorological stations in Argentina, Brazil, Paraguay, and Uruguay from the database of the European Communitys Sixth Framework Programme A Europe–South America Network for Climate Change Assessment and Impact Studies in La Plata Basin (EU FP6 CLARIS LPB), with some additional data series. This gridded dataset is new for the region, not only for its spatial and temporal extension, but also for its temporal resolution. The region for which the gridded dataset has been developed is 20°–40°S, 45°–70°W, with a resolution of 0.5° latitude × 0.5° longitude. Since the methodology used produces an estimation of gridbox averages, the developed dataset is very useful for the validation of regional climate models. The comparison of gridded and observed data provides an evaluation of the usefulness of the interpolated data. Acc...

Intercomparison of four different Southern Hemisphere sea level pressure datasets

Abstract Two different sea-level pressure datasets for the strip between 20° and 40°S are intercompared. At large space-time scales the sets are virtually identical. However, for studies of short-term, regional changes caution must be exercised because the datasets may differ substantially.