Spatial and Temporal Patterns of Net Primary Productivity in the Source Regions of Yangtze and Yellow Rivers

Abstract

Based on remote sensing data, climatic data and other related data in source regions of the Yangtze and Yellow Rivers from 2000 to 2006, the net primary production (NPP) of source regions of the Yangtze and Yellow Rivers was estimated by using CASA (Camegie-Ames-Stanford Approach) model. Spatial pattern and changing tendency for vegetation NPP, and correlation relationships between air temperature, precipitation and NPP were analyzed. The results showed that annual average NPP in source regions of Yangze and Yellow Rivers was 104.22 gC.m-2.a-1. A total mean annual NPP in source regions of Yangtze and Yellow Rivers was 22.07×1012g C.a-1, which decreased from southeastern to northwestern part and this trend coupled with the changes in temperature and precipitation. Increasing trend of NPP in source region of Yellow River was clearer than that in source region of Yangze River during 2000-2006. The region with increasing tendency occupied approximately 68.42% of total area, while the region with decreasing tendency accounted for 23.83%. Marked decrease regions for NPP were mainly distributed in the southeastern source region of the Yellow River including Gande county, Dari county, Maqin county and area nearby Dari river and Kequ, occupied 10.56% of total source regions area. The region of very marked increase sporadically distributed in the region with marked increase trend. The northwestern region of Yellow River and southeastern region of Yangtze River were located by region with indistinct increase extensively. Regression analysis of vegetation NPP and climate factors showed that average temperature and precipitation were important factors affecting changes in vegetation NPP; while the mean air temperature appears to be the primary factor controlling terrestrial NPP in the source regions of Yangze and Yellow rivers.