Climate Assessment And Climate Changes During The Last 54 Years In Three Gorges Reservoir

Three Gorges Reservoir is the reservoir flooding area affected by backwater after the establishment of Three Gorges Dam, as well as the administrative district referring to emigration and allocation. The Three Gorges Reservoir is a narrow area with the shape of east-west length and north-south narrow, which also has complicated topography, sharp discretion elevation, and big differences of east and west climates. The climate here has the traits of warm in winter, aridity in spring, hot in summer, rainy in fall, lack of sunshine and excessive cloud and mist, which is belong to sub-tropical and monsoonal climate, in addition, the vertical change is notable. Ecological environment in this area is extremely fragile often with the disasters of landslide, coast and mud-rock flow. The frequency of summer aridity is up to 80%～90%. Long cultivating sloping field, deforestation and other unreasonable actions lead to badly soil erosion and eco-system maladjustment. It is of great significance to know of the climatic traits in Three Gorges Reservoir.After the construction of the Three George Reservoir, the water level of the reservoir has raised up, and the area of perennial water has increased much, which would affect the local climate ecological environment. The change of underlying surface would lead to the local weather system's formation, evolvement and the change of behave characteristic, and that result in the change of local climate characteristic, which also lead to the change of local weather disaster frequency, degree and distribution character. Climate change must induce ecological environmental change, and affect human's agricultural activities, which feed back the climate ecological system. Therefore, the study of climate change of the Three George Reservoir has great significance.Reservoir climate integrated assessment is the basis of the Three George Reservoir climate change. Based on the meteorological data about the 34 meteorological stations during the period of 1973 and 2002 in the Three Gorges Reservoir, annual mean temperature, accumulated temperature＞10℃, desiccation index, annual precipitation and precipitation variability were obtained. "Multiple regression model + Inverse Distance Weighting (IDW) residuals" was used to interpolate meteorological index, and climatic thematic maps with a spatial resolution of 100m were produced. With the method of Analysis Hierarchy Process (AHP), the model of integrated climatic evaluation in the Three Gorges Reservoir was established. The results showed that the water and heat resource was abundant, the annual mean temperature was mainly between 12℃and 19℃, accumulated temperature＞10℃was 4795℃on average, desiccation index was less than 1, the annual precipitation was mainly between 1100mm and 1500mm, and the precipitation variability was a range of 10 to 15 percents. The average value of integrated climate evaluation was 5.3. The climate in southwest and middle area was better than that in the east. The climate grade of the east was 5 which was the lowest. The climate in the middle region was quite different between the south bank and the north bank of the river. The climate grade in the north part was above 5, while the climate grade in south part was between 4 and 6, and the southwest was above 6.Based on the meteorological data about the 34 meteorological stations during the period of 1951 and 2004 in the Three Gorges Reservoir and its neighboring, the climate change characters of recent 50a were studied. mean temperature, maximum temperature, minimum temperature, the diurnal temperature range (DTR), and rainfall are analyzed on seasonal and annual time and special scales. The results showed that annual mean temperature in summer had decreased with the trends -0.16℃per decade; minimum temperature in winter had increased with the trends 0.2℃per decade; maximum temperature in summer had decreased with the trends -0.21℃per decade; the annual mean DTR had decreased with the trends -0.1℃per decade, especially in the winter and spring, the decreasing trends were notable. The imbalance change of maximum temperature and minimum temperature led to the change of day temperature difference. The decreased day temperature difference in summer was mainly on the account that falling speed of maximum temperature was faster than that of minimum temperature. Furthermore, the decreased day temperature difference in winter was mainly on the account that rising speed of minimum temperature was faster than that of maximum temperature. Annual mean temperature, annual mean minimum temperature, maximum temperature and day temperature difference were all in the ascending trend during the 25 years from 1980 to 2004, above all, the temperature in winter increased dramatically, the rising trend of maximum temperature was sharper than that of minimum temperature. From 1951 to 2004, there was a gradual decreased trend in the precipitation in spring and fall and an increase in summer, in winter it remained stable. Between 1980 and 2004, the annual precipitation descended, the precipitation in spring and winter rose, while that in summer and fall fell. Since the construction of the Three George Reservoir, mean temperature, maximum temperature, minimum temperature and diurnal temperature range all have the trend of move up, especially in spring, fall and winter. The change range of precipitation varied greatly. Precipitation in 1997 and 2001 were fairly low, and in 1998 was the highest of the recent 54a.