Using GIS to Investigate Spatial and Temporal Variations in Upland Rainfall

A method is presented for conditional analysis of spatial and temporal (1961-2007) variations in rainfall under different synoptic situations and different geographic sub-regions, using Cumbria in NW England as a study area. A daily synoptic typing scheme, the Lamb Weather Catalogue, was applied to identify rainfall under three different weather types: south-westerly (SW), westerly (W) and cyclonic (C). Topographic descriptors developed using GIS were used to classify rain gauges into six geographic sub-regions: coastal, windward-lowland, windward-upland, leeward-upland, leeward-lowland, secondary upland. Examining temporal rainfall trends associated with different weather types, in different geographic sub-regions, reveals useful information on changes in rainfall processes. The total rainfall under SW and W weather types is increasing, particularly in upland regions. The increase in SW rainfall is driven by more frequent wet-days, whereas the increase in W rainfall is driven by increases in both wet-day frequency and yield per wet-day. The rainfall under C weather types is decreasing. Combining GIS and synoptic climatology gives insights into rainfall processes under a changing climate. The conditional analysis method can be applied at both local and regional scales, and its success is largely due to the ability of GIS to integrate, visualise, and efficiently model spatial data.