Precipitation global average

The overall rainfall rate and amoimt depend on these microphysical processes and even more greatly on the initial amount of water vapor present, and on the vertical motions that transport water upward, cool the air, and cause supersaturation to occur in the first place. Thus the delivery of water to the Earth s surface as one step in the hydrologic cycle is controlled by both microphysical and meteorologic processes. The global average precipitation amounts to about 75 cm/yr or 750 L/(m yr). 

In conclusion, we must still count on considerable inaccuracy even in such general quantities as the change in global average temperature and precipitation—and this is when the forcing of climate is known exactly ... 

Usable freshwater comes from rainfall over land, about 120 000 km per year. Approximately 62% evaporates from the land surface into the atmosphere. The difference between precipitation and evaporation is the runoff of the rivers (95% of total runoff) and a small amount of groundwater runoff into the oceans. The total runoff is conventionally termed as renewable water resources, and is estimated at 43 000km per year (Shiklomanov, 2000). The renewable water resources are very variable with space and time, and not all of the renewable water is accessible for use because part of it flows into remote rivers and seasonal flood waters that cannot be captured before they reach the oceans. According to the literature, 20-30% of the renewable water resources is all that is economically available for human use (Sophocleus, 2004), that is, today (2010) about 4m per capita and day on a global average. 

The long-term global average precipitation rate ((/r) is 9.7 x 10 m/h, equivalent to 0.85 m/year, and this value has been recommended as a generic value for chemical fate modeling [6,21], However, rain rate is highly variable geographically and seasonally. 

Water is present in three aggregate states solid, liquid and vapor. Of the estimated global water resources of 1386 million cubic kilometers, however, only 0.001% or 0.013 km is stored in the atmosphere as water vapor (Table 1, [4]). If fully released, this volume of water would produce 25 mm of precipitation depth globally. Given an average annual and global precipitation of 972 mm [5], the water vapor in the atmosphere must therefore be completely replenished at least 39 times per year or approximately every nine days. 

These along with other data about various parameters of the environment cannot be considered sufficiently complete to resolve the many problems of global ecodynamics studies, since they were not gathered with solution of these problems in mind. The natural anomalies observed in the last decade characterized by fewer cold periods, intensified wind speed in tropical cyclones, and other abrupt deviations from average trends of temperature and precipitation, cannot be formally explained. The reason is that available data are either superfluous regionally or inadequate globally. 

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