| During the last 40 years, the runoff in some mid-latitude areas had significantly reduced as the result of climatic drying, land use changes and other human activities. In case of that, the life of migrants would be seriously threatened. However, the effects of climate change and landuse change on runoff and the temperal and spatial differences are not clear. It refines the scientific arrangement for water resource and reflection for climate change. In this study, the depth of runoff, sediment yield, climate and landsue from 1966 to 2005 were analysed, based on monthly hydrology data and daily meteorology data from 11 hydrology station and 14 meteorology station of Jinghe Basin from 1966 to 2005. Moreover, statistical method are used to quantitively analyse the contribution of climate change and landuse change to runoff change and their temperal and spatial difference. Results are listed below:(1)Runoff change Runoff had significantly reduced in Jing River Basin during the last 40 years. The annual depth of runoff was 43.1mm in the period of 1966-1975, and reduced to 22.7mm in the period of 1996-2005, with a reduction of 47.3%. The depth of runoff in spring and autumn had significantly reduced from 7.4mm and 15.4mm of 1966-1975, to 3.2mm and 6.7mm of 1996-2005, reduced for 57.3% and 56.3%. The depth of runoff in summer had reduced from 16.0mm of 1966-1975, to 10.6mm of 1996-2005, reduced for 33.7%. The depth of runoff in the West subregion and the South subregion had reduced for 60.8% and 61.6%. Variation of runoff were different among subregions. The depth of runoff in the west subregion and the south subregion had significantly reduced from 133.7mm and 44.8mm of 1966-1975, to 52.4mm and 17.2mm of 1996-2005, reduced for 60.8% and 61.6%. The depth of runoff in the central subregion had reduced from 32.1mm of 1966-1975, to 20.3mm of 1996-2005, reduced for 36.8%. The depth of runoff in the north subregion had increased from 20.2mm of 1966-1975, to 21.2mm of 1996-2005, increased for 4.9%.(2)Sediment yield change There was a strong annual sediment yield from Jinghe Basin in the 1960's, it was 302.49 million t/a for the total river basin and the corresponding annual sediment modulus was 6672 t/km2/a on average. There was a visible spatial heterogeneity of annual sediment yield within the basin. The total area of river courses being at the sediment yield intensity grades of"extreme"and"severe"accounted for 72.6% of the total basin area, which yielded 86.0% of the annual sediment yield of the total basin. Since 1970's, the annual sediment yield of Jinghe Basin has been reduced. Compared with that of 1960's, the average of annual sediment yield for the whole basin in 1990's was reduced to 265.78 million t/a, with a reduction ratio of 12.1%. However, 93.5% of this sediment reduction took place in the river courses being at the"extreme"grade of sediment yield intensity.(3)Climate change Drought turned more serious in Jing River Basin over the last 40 years. For example, the annual drought intensity (NDDS) had increased from 48.2 days/year in the period of 1966-1975 to 69.1 days/year in the period of 1996-2005, increased for 43.4%. Meanwhile, drought area of different seasons were all enlarged. The drought area stronger than that of slight degree of spring, summer, autume and winter had increased from 16.5%, 20.3%, 21.4% and 11.9% in 1966-1975, to 50.4%, 48.0%, 51.7% and 47.9% in 1996-2005, increased for 2.1, 1.4, 1.4 and 3.0 times. Climatic drying were also different among subregions. The central subregion was the most obvious for drying. The annual drought intensity had increased from 45.8 days/year in the period of 1966-1975 to 68.5 days/year in the period of 1996-2005, with an increase of 49.8%. The annual drought intensity of the north subregion had increased from 55.5 days/year in the period of 1966-1975 to 75.8 days/year in the period of 1996-2005, with an increase of 36.6%.(4)Landuse change Under the impacts of human activities on landuse, forest and farmland in Jinghe Basin had increased. Meanwile, grassland and other landuse type, such as urban land and water had decreased. From 1986 to 2000, the area ratio of forest and farmland had increased from 39.8% and 8.2%, to 57.8% and 25.3%, increased for 18.0% and 17.1%; Grassland had decreased from 50.4% to 16.6%, decreased for 33.8%; urban land and water had decreased from 1.6% to 0.3%, decreased for 1.3%.However, the change of area ratio for different landuse types were not the same among subregions. The area ratio of farmland of the south subregion, the west subregion, the central subregion and the north subregion had increased from 54.8%, 37.5%, 36.0% and 32.6% in 1986, to 55.0%, 48.4%, 58.8% and 64.4% in 2000, increased for 0.2%, 10.9%, 22.8% and 31.8%. The area ratio of forest of the south subregion, the west subregion, the central subregion, the north subregion had increased from 11.9%, 11.6%, 9.0% and 3.0% in 1986, to 38.5%, 31.8%, 25.4% and 6.1% in 2000, increased for 26.6%, 20.2%, 16.4% and 3.1%. The area ratio of grassland of the north subregion, the central subregion, the west subregion and the south subregion had decreased from 64.1%, 53.2%, 48.3% and 31.1% in 1986, to 29.4%, 15.5%, 19.4% and 6.0% in 2000, decreased for 34.7%, 37.7%, 28.5% and 25.1%. The area ratio of urban land and water of the north subregion, the central subregion, the west subregion and the south subregion had decreased from 0.3%, 1.8%, 2.6% and 2.2% in 1986, to 0.1%, 0.3%, 0.4% and 0.5% in 2000, decreased for 0.2%, 1.5%, 2.2% and 1.7%.(5)Effects of climate change and landuse change on runoff During the period of 1996 to 2005 that the annual depth of runoff of Jinghe Basin had significantly reduced for 20.4mm (47.3%), the climate were severely drier (the annual drought intensity had increased for 43.4%), and the landuse change was not obvious. Climate change made the annual depth of runoff reduced for 17.8mm, and the contribution rate for total reduction of runoff was 87.0%. Landuse change made the annual depth of runoff reduced for 2.6mm, and the contribution rate for total reduction of runoff was 13.0%.However, the effects of climate change and landuse change to runoff were not the same among seasons. The runoff had reduced significantly in spring and autume. The annual depth of runoff had reduced for 12.9mm, which accounted for 63.2% of the year. During the reduction, the contribution rate of climate change was 87.0% and 88.4%. The annual depth of runoff of summer had reduced for 5.4mm, which accounted for 26.5% of the year. During the reduction, the contribution rate of climate change was 97.8%. The annual depth of runoff of winter had only reduced for 2.2mm, which accounted subtle of the year. During the reduction, the contribution rate of landuse change was 56.4%, higher than 43.6% of climate change.The effects of climate change and landuse change to runoff were also not the same among subregions. As the originate area of Jinghe river, the annual depth of runoff of the west subregion had reduced 81.3mm, reduced for 60.8%. During the reduction, the contribution rate of climate change was 70.7%. The annual depth of runoff of the south subregion had reduced 23.3mm, reduced for 52.0%. During the reduction, the contribution rate of climate change was 98.8%. The annual depth of runoff of the central subregion had reduced 11.8mm, reduced for 36.8%. During the reduction, the contribution rate of climate change was 134.1%, which led the reduction of runoff for 15.8mm. The contribution rate of landuse change was -34.1%, which led the increase of runoff for 4.0mm. The annual depth of runoff of the north subregion had increased 1.0mm, increased for only 5.0%. During the reduction, the contribution rate of climate change was 444.2%, which led the slight reduction of runoff. The contribution rate of landuse change was -544.2%, which led the slight increase of runoff. |
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