page_title: Global Energy and Water Exchanges
section_title: Precipitation Assessment Group
hierarchical_section_title: Global Energy and Water Exchanges / Panels / GEWEX Radiation Panel / Global precipitation climatology project / Precipitation Assessment Group
caption_attribution_description: English: View of the crescent moon through the top of the earth's atmosphere. Photographed above 21.5°N, 113.3°E. by International Space Station crew Expedition 13 over the South China Sea, just south of Macau (NASA image ID: ISS013-E-54329). Français&#160;: Photo des couches hautes de l'atmosphère terrestre. Polski: Zdjęcie górnych warstw atmosfery ziemskiej z widocznym przejściem w przestrzeń kosmiczną. Ελληνικά: Η Γήινη ατμόσφαιρα, η φωτογραφία ελήφθη από το διάστημα κι ύψος 335 χιλιόμετρα
context_page_description: The Global Energy and Water cycle Exchanges project is an international research project and a core project of the World Climate Research Programme.
  In the beginning, the project intended to observe, comprehend and model the Earth's water cycle. The experiment also observes how much energy the Earth receives, studies how much of that energy reaches surfaces of the Earth and how that energy is transformed. Sunlight's energy evaporates water to produce clouds and rain, and dries out land masses after rain. Rain that falls on land becomes the water budget which can be used by people for agricultural and other processes.
  GEWEX is a collaboration of researchers worldwide to find better ways of studying the water cycle and how it transforms energy through the atmosphere. If the Earth's climates were identical from year to year, then people could predict when, where and what crops to plant. However, instability created by solar variation, weather trends, and chaotic events creates weather that is unpredictable on seasonal scales. Through weather patterns such as droughts and higher rainfall these cycles impact ecosystems and human activities.
context_section_description: The Precipitation Assessment Group was assigned by the panel to evaluate data on precipitation emphasizing data in the Global Precipitation Climatology Project (GPCP) product (GRP project). The GRP prepares to assimilate data from GPCP diurnal variation data for better estimation of the global precipitation products. The result of 25 years of measurement the global average precipitation rate is 2.61 mm per/day (about 0.1 inch/day) with about 1% uncertainty. The finding suggests there is no significant variation in mean annual rainfall. Regional variation was separated from land and ocean and the land variation of received precipitation was greater than the ocean. Satellites used to train the dataset analysis have the flaw of not having inaccurate measurements of drizzle and snow, and lack measurements in isolated places and over oceans. The rainfall maps show the greatest absolute rainfall error over the tropical oceans in regions with the highest estimated rainfall. The report self-critiques two aspects: the lack of polar-crossing satellites at the beginning of the study and the inability to correlate new information and older information (ground-based measurements). The noticeable trends in the dataset were deemed insignificant with regard to issues like global warming, but some stand-out positive trends over the Indopacific region were notable (Bay of Bengal and Indochina) and negative trends over South Central Africa.
caption: A goal of GEWEX is to monitor radiation that is released at the top of the atmosphere and model how energy flows from earth surfaces back into space.
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