Land-use, water resources and nitrogen load in major river basins in Asia

摘要

At present, 55% of the population in the world lives in Asia. Rice is the staple food of Asians. Are there sufficient water resources for cultivating crops? Will the water quality remain suitable for cultivating crops? To obtain basic data for these questions, we analyzed the land-use/land-cover in Asia and constructed nitrogen load maps. Rice is mainly cultivated from East to South Asia. We used 0.5°grid data to estimate the nitrogen load in these regions. These data include those on the course of a river, land-use/land-cover classification, population, climate, nitrous oxide (NOX) emission, and country boundary. We also used statistical data on fertilizer consumption, food production, food consumption and food trade. In East Asia, the area of grassland is larger than that of woodland due to a low precipitation. The area of cropland is almost the same as that of grassland. In Southeast Asia, woodland predominates grassland due to a high precipitation. The next predominant land-use is cropland. In South Asia, cropland is predominant for feeding the large population. There is no more space for extending the cropland area. The nitrogen load changes seasonally according to cropping systems used and precipitation. The rate of denitrification is similar to the nitrogen load and the water quality is good at present. In the future, the water quality would deteriorate due to an increase in the nitrogen level discharged from humans, fertilizer consumption and NOX emission.