Comparison and analysis of precipitation surfaces produced by CI and IC two approaches in Loess Plateau

Collecting precipitation at 74 stations in/around Loess Plateau Region from 1952 to 2001,surfaces of annual average precipitation and linear trend of Loess Plateau from 1952 to 2001 were interpolated with ARCGIS 9.3 using Geostatistical Analyst adopting "calculate then interpolate"(CI) and "interpolate then calculate"(IC) approach.The Result showed that: 1) Total annual average precipitation of Loess Plateau from 1952 to 2001 and its linear trend coefficient were 421.65 mm,421.56 mm and-0.462 1 mm/a,-0.423 1 mm/a respectively.Similarity coefficients of them were 99.78% and 95.99%,which showed a good accordance between them.2) Surfaces produced by IC approach were a little smoother than that by CI approach.Terrain analysis methodology was a visualizing method of evaluating the precision,smoothness,the spatial amount change and direction change of precipitation surface and linear trend surface.3) Area of decreasing direction of spatial trend of precipitation was mainly from Southeast to Northwest,then South to North,Southwest to Northeast and East to West where is up to 89.34% of Loess Plateau,which can be regarded as zonality distribution law.The others which belonged to non-zonality distribution law are 10.66%.4) Precipitation of Loess Plateau from 1952 to 2001 has a significant decreasing trend with an average linear trend coefficient of-0.541 0 mm/a by CI approach or-0.423 1 mm/a by IC approach.