POINT CUMULATIVE SEMIVARIOGRAM OF AREAL PRECIPITATION IN MOUNTAINOUS REGIONS

Assessments of average annual precipitation (AAP) are necessary for hy drological studies of a watershed for various water resources activiti es. Although AAP isohyetal maps provide global information, the behavi or of precipitation occurrence al and around any individual station ca nnot be assessed from such maps. For this purpose, the point cumulativ e semivariogram (PCSV) concept is presented and applied to precipitati on records from Yucca Mountain, NV, USA. These PCSVs provide qualitati ve interpretations that are subsequently convertible to simple quantit ative relationships for predictions. Further, PCSV provides informatio n about the nugget effect, radius of influence, structural changes etc . within the regional variations in the precipitation event around eac h station. The application revealed that Yucca Mountain annual precipi tation amounts are not regionally homogeneous but have three distincti ve types of homogeneity subregions. In the first category there is no nugget effect in the regional precipitation around the site concerned whereas there is significant regional dependence at small distances fr om the site. The second category includes a rather perfect regional re lationship around the station concerned up to a certain distance and t hen onwards there is an abrupt region of independence. Finally, the la st category implies that the precipitation amount at a station accumul ates due to local convective rainfall events. (C) 1998 Elsevier Scienc e B.V.