I was able to write most of this book directly from personal experience gained at the Institute of Hydrology (now the Centre for Ecology and Hydrology) in Wallingford from 1964 to 1988 and since then as a consultant in the same disciplines. This whole period has also been regularly interspersed with overseas travel, advising on data collection for water resources, flood warning and agricultural projects. These trips have taken me to about as many remote locations around the globe as David Attenborough has visited in his film making, places rarely seen by outsiders. On these many and diverse missions, from the Antarctic to tropical rainforests and deserts, I came face to face with the complex reality of environmental monitoring and the many problems that obtaining good measurements presents.

When it came to writing Part 4, I needed input from those directly involved in collating, homogenising and analysing the data collected by the global network of raingauges, and more recently by satellites. In this I was helped greatly by David Parker, Jen Hardwick and Chris Folland at the Hadley Centre in Exeter, who supplied me with data and graphs showing long-term precipitation trends in England and Wales, and who helped by passing on some of my questions to others with different specialised knowledge. In consequence I also had a useful and interesting exchange of emails with Aiguo Dai, Kevin Trenberth and Ping Ping Xie all at the National Center for Atmospheric Research in Boulder, Colorado.