The temperature of the upper reaches of the Yellow River, the second longest river in China, is clearly relevant with the world-wide warming trend, according to a study conducted by CAS researchers and their colleagues from administration of hydrology and water resources of the Upper Reaches of the Yellow River. Due to the possible temperature hike and drastic decline in local precipitation, the runoff in the reaches may face a trend of continued decrease over the next decade, they warn.
The prediction is made after an analysis of the characteristics, possible causes and trends of variations of temperature, precipitation and runoff in the upper Yellow River basin using the hydrological and meteorological data over the past 50 or so years at some observation stations, report the scientists in a recent issue of the Journal of Glaciology and Geocryology.
The study forecasts the possible changes of runoff over the Yellow River Basin under global warming scenarios, notes Prof. Lan Yongchao, lead author of the article and an expert in forecast models of long and mid-term river runoffs and water resources from the CAS Cold and Arid Region Environmental and Engineering Research Institute.
The upper portion of the Yellow River to which he refers in the study is the Yellow River drainage area above Tangnag in the northeastern part of the Qinghai Tibetan Plateau, notes Prof. Lan. Although the topography is high and cold and signs of human habitation sparse, the valley above tangnag is the source of more than 40% of the Yellow River's water, and the collection area comprises 16.2% of the Yellow River's total drainage area. The place is also the general exit for the Yellow River headwaters region; all the water flows through this point to its next stop--Longyangxia Reservoir.
In order to forecast changes in upper Yellow River water levels under these climatic conditions, Lan's group sequenced 63 possible climate combinations, with temperature rise ranging from no change to 3°C and precipitation fluctuating in a range of 20% increase to 20% decrease. The most beneficial of these climate combinations maintained temperature at the current level and increased precipitation 20%; the worst combination caused a 3°C rise in temperature and a 20% drop in precipitation. In the former scenario, the study indicates, the increase range may be more than that of precipitation because of the synchronously increasing supply of meltwater from snow, glaciers and frozen soils. In the latter scenario, then the amount of water in the upper reaches of the Yellow River will decrease 50% or more from the present level.
Studies show that due to the changes in the heating conditions and reorientation of the atmospheric currents, it is inevitable to give rise to the renewal of the water cycle and temporal and spatial redistribution of the water resources so that both the ecological setting and socio-economic development in a region will be influenced. The latest decade saw the highest record in the average temperature per year since the beginning of meteorological observation about 140 years ago in the River's upper reaches. In the same context, the decade registered the lowest annual runoff during the past 50 years since the region has its own hydrological records, including the minimal incoming river water flow in 2002 at the hydrological station's cross-section. The big-margin decrease in the incoming flow volume not only comes across disastrous losses in the northwestern China's power grid, in which hydropower plays a predominant role but also greatly imposes a restraint on the development of the whole valley of the Yellow River even the regional GNP of the north China on the whole. The research project predicts the global warming-up trend will be going on in the 21st century, averaging a rise up to 1.5 - 4.5°C in the temperature on ground surface. The sustained and steady trend will lead to an intensified tension in the water-supplying situation which has been so far becoming oppressively tense in the River valley.
The experts suggest that, in consideration of the further demands posed by the regional growth in the socio-economic development in coming years and the uncertainty in the local precipitation in the upper reaches, the overall hydrological situation will be menacingly grim. Thoroughly to do away with the issues by uprooting them, it is advisable to make the waterworks operational in the western part of the national program to shift water from the water-rich south to the arid north in an early date.
