Book contents
- Frontmatter
- Contents
- Preface
- Acronyms and abbreviations
- Part 1 Past theories of rain and snow
- Part 2 Present theories of precipitation
- Part 3 Measuring precipitation
- Part 4 The global distribution of precipitation
- 12 Raingauge and satellite datasets
- 13 Precipitation means and trends
- 14 Precipitation variability and extremes
- Part 5 Future developments
- Index
- References
13 - Precipitation means and trends
Published online by Cambridge University Press: 10 October 2009
- Frontmatter
- Contents
- Preface
- Acronyms and abbreviations
- Part 1 Past theories of rain and snow
- Part 2 Present theories of precipitation
- Part 3 Measuring precipitation
- Part 4 The global distribution of precipitation
- 12 Raingauge and satellite datasets
- 13 Precipitation means and trends
- 14 Precipitation variability and extremes
- Part 5 Future developments
- Index
- References
Summary
Limitations of the datasets
If we are interested in how precipitation has changed over the long term we have to rely entirely on raingauge measurements because only they provide a long enough run of data. It will be clear from the foregoing chapters, however, that raingauges are installed mostly on the land with just a few operating on islands to cover the oceans. This means that the greater proportion (71%) of global precipitation is not measured. Even on land, coverage is patchy, with large areas without raingauges, resulting in only about 25% of the earth's surface being covered.
In addition it will be clear from Chapter 8 that even the raingauge data that we do have will be error-prone due to raingauge shortcomings, in particular wind losses, and the situation is worse for snowfall because of increased aerodynamic errors. Finally, conversion from point measurements to areal averages in cells of 0.5° × 0.5°, 1° × 1° or 2.5° × 2.5° latitude and longitude also introduces some uncertainty. Since around 1980 satellite measurements have become available and this is improving geographical cover, especially over the oceans and remote land regions. But 25 years is not sufficient to detect long-term trends. In addition, the accuracy of remotely sensed precipitation is still difficult to quantify, and because the better instruments are on polar-orbiting satellites temporal cover is still limited, giving just a brief glimpse of rain events as the spacecraft passes by a few times a day.
- Type
- Chapter
- Information
- PrecipitationTheory, Measurement and Distribution, pp. 246 - 257Publisher: Cambridge University PressPrint publication year: 2006