Spatial properties of seasonal rainfall in southeast England
Marie Ekström and Adrian Chappell

Interpolated rainfall fields are important inputs to agricultural, hydrological and ecological models and serve to enhance our understanding of environmental systems and hence the natural and anthropogenic impacts on the surface environment. However, the large temporal and spatial variability in rainfall makes this variable difficult to estimate at unsampled locations, particularly when station network is highly dispersed. In this article, we present preliminary work within the Marie Curie Framework 6 project GAP (Geostatistical Analysis of Precipitation). Using one year of rainfall data, seasonal rainfall patterns are investigated for South East England. Both seasons showed anisotropic conditions with greater dependence in the W-E direction. The parameters of the models fitted to the directional variograms showed a larger range, but substantially smaller sill, for the summer season compared to those variograms of the winter season. Seasonal rainfall depth maps were derived using Simulated Annealing (SA) and Ordinary Kriging (OK). The two methods showed large differences in terms of local and regional variability, with smooth patterns associated with the OK maps and larger spatial variability associated with the SA maps. Both methods however, captured the large scale patterns that are typical to summer and winter rainfall in the study region. We suggest that the optimized patterns using SA could provide an alternative to OK, particularly for high temporal resolution rainfall data when OK produce unrealistically smooth maps.

Investigating the role of surface water vapour content changes in recent climate
Katharine Willett

Atmospheric water vapour plays a key role in the climate system. In the light of recent changes in global annual mean temperatures, the quantification of recent changes in water vapour content will be a valuable tool to our understanding of the climate system. This project attempts to further work of others such as New et al. (1999, 2000) in producing a comprehensive gridded global product of monthly mean surface vapour pressure. It will combine hourly data from the Hahn (1971 - 1996) and ISH NCDC (1945 - 2003) datasets with Mark New's monthly mean vapour pressure (1961-1995) and marine data from ICOADs. Homogenisation technique and methods for creating monthly means will be a particular focus. Finally, the global product will be used in comparison with model output from various runs of the Hadley Centre models (HadCM3 / HadGEM) to address the question as to whether the models adequately resolve both the variability and trends.

Variability and Extremes of Rainfall at Different Spatial Scales
Carol McSweeney

Issues of spatial scale present a number of problems in the evaluation and application of climate model output. Whilst the mean is unaffected by spatial scale, the distribution of daily rainfall totals will alter depending on the size of the area represented such that the variance, for example, of daily rainfall observations at a point will be greater than that of a regional average surrounding that station. It is generally accepted that climate models generate output which represents the grid-box scale, which presents us with a mismatch between
a) the point observations used to evaluate model output; and
b) the resolution of scenarios required for many areas of climate impact assessment.
The high degree of spatial and temporal variability in precipitation, and the particular interest in the magnitude of that variability and extremes of the rainfall process, mean that this issue is of particular importance in assessments of model skill and future scenarios of change in precipitation regimes.