The Theissen Polygon method calculates the weighted average of each precipitation station
in and near the watershed based on the following relationship:
The mean monthly precipitation amount, air temperature, and mean weighted precipitation [delta][sup.18]O values in the sampling period for each precipitation station
of the GNIP are shown in Figure 3.
The most widely used record of the changing water cycle over land is from long-term precipitation station
data (e.g., Peterson and Vose 1997; Menne et al.
The researchers culled the data to focus on stations that have been active for at least 10 years, which amounted to 43,121 precipitation stations
and 5,317 streamflow stations.
The selection of precipitation stations
was based on the closeness of stations to subbasins (Figure 2).
of the Ministry of Regional Municipalities and Water Resources reported the highest amount of rainfall in the Governorate of Muscat, with 55 mm in the Wilayat of ASeeb.
The minimum densities recommended of precipitation stations
by the WMO are 1 station for 250 [km.sup.2] for the mountainous area, 1 for 900 [km.sup.2] for the coastal area, and 1 for 10 [km.sup.2] for urban areas .
The precipitation data originate from 27 meteorological, 64 hydrological and 16 precipitation stations
To analyse the Estonian mean amount of wet and dry days and their annual distribution in the last 50 years, we have counted the 10- and 20-day moving average of precipitation through the precipitation data in 1957-2006 of 56 Estonian meteorological and precipitation stations
Additional precipitation stations
were installed on the small watershed, which increased the total to 230.