EFFECT OF IRRIGATION ON RUNOFF AND LOCAL CLOUD SYSTEMS IN THE YELLOW RIVER BASIN
Authors: Xieyao Ma and Hiroaki Kawase
Abstract: The Yellow River basin, which is located in an arid to semi-arid region of northern China, is one of the largest irrigated areas in the world and has suffered from chronic severe water shortages in recent decades. To sustain local rural communities and maintain food security, water-saving irrigation measures are required. In this chapter, we used numerical modeling experiments to examine the effects of water-saving measures. A hydrological model was used to simulate the effects of lower water use on river runoff, and a regional climate model was used to investigate the influence of irrigation on the atmospheric vapor system. The hydrological modeling demonstrated that water-saving irrigation had significant effects at the Toudaoguai hydrological gauge downstream from the Qingtongxia and Hetao irrigation districts and at the Sanmenxia gauge downstream from the Weihe and Fenhe irrigation districts. For three progressively higher levels of water savings, annual runoff in the period 1980-2001 increased by approximately 26.8, 53.8, and 88.5% at Toudaoguai and 31.6, 62.1, and 97.2% at Sanmenxia, respectively. The annual mean discharge at Huayuankou was maintained at > 420 m3/s, which is more than the minimum ecological discharge of 170 m3/s for that station. A cloud-formation experiment was conducted after confirming that satellite-observed cloud distributions were properly simulated. Land-use- induced circulation inhibited cloud formation over the Hetao Irrigation District and transported water vapor from the irrigated area to the surrounding dry area, contributing to cumulus cloud formation over the surrounding dry area.