| Popis: |
Climate change resulting from greenhouse gases has attracted growing interest among a wide area of scientific investigation. The impacts of global warming on hydrological environment in terms of both quantity and quality are, how-ever, left for further verification based on the accumulation of highly precise observed data. The purpose of the present paper is to elucidate the impacts of global warming on water sustainability with a research focus on the transformation in river water temperature and quality in the drainage basin with meso-spatial scale under the humid temperate climate. As a background, secular trend in variability of the meteorological components including annual mean air temperature and annual precipitation was comparatively inspected by using instrumental records over the last 140 years. Smoothed trend curve on long term changes in annual mean air temperature at the Tokyo Regional Headquarters, Japan Meteorological Agency, has tended to rise since the mid-1950s. On the other hand, annual precipitation has been inclined to be below the average in the period through 1960s into the first half of the 1980s. It is pointed out that the notable characteristics on cur-rent frequency-magnitude distributions in annual precipitation are both the reduction of interval of hydrological extremes and the increase of range in each year. Annual runoff ratio on the basis of the runoff calculated from the difference between precipitation and potential evapotranspiration has a positive correlation with annual precipitation in the lower reaches of the Kumozu River. This fact suggests that a trend curve of the long-range change in the annual runoff ratio is dominated by annual precipitation. In addition, average year values of annual runoff ratio and annual precipitation have shown a tendency to decrease during the last 120 years. Long term changes in water temperature of the Tama River as expressed by moving average from 1973 onward are analogous to those in air temperature. In the period from 1876 up to 2019, the highest value of annual mean air temperature in Tokyo was recorded in 2004, and the minimum one of annual precipitation occurred in 1984, respectively. Under the condition of those extreme hydrometeorological events, the water quality of the Tama River showed a remarkable change as compared with its average value in normal year. The most strik-ing features on water quality due to high water temperature and small discharge were higher concentration of COD and lower value of the saturation of dissolved oxygen. Although a comparative consideration on the results in the study basin with those in the different climatic region is a task to be solved, the outcome identified in the present paper would provide a meaningful perspective on the possible consequences in evaluating the impacts of future climate change on the hydro-logical environment. |
