Impacts Of Human Activity And Climate Change On Evapotranspiration In The Tarim River Basin

The Tarim River Basin(TRB) is a typical arid inland river basin, Water resources, although rare, plays an indispensable rolein maintaining fragile ecological environment and supporting human economic and social development here. In the past 20 years, the hydrological processes and wat er resources situation of the Tarim River Basin is effected significantly by climate change and human activities(mainly for the expansion of agricultural irrigation). Based on the meteorological data for nearly 30 years and land use data for nearly 20 years, we analysis the change trends of precipitation and air temperature, and the transformation among land use types. A land surface model is built and a set of numerical experiments under different scenarios are carried out to investigate the imapacts of climate change and land use changes on evapotranspiration and irrigation. Further more, comprehensive analysis of impacts of environmental change on hydrological processes and water resources situation changes in the Tarim River Basin is conducted. The main results are as follows:(1)During the past 30 years, annual precipitation in the Tarim River Basin increases with fluctuation. The largest increace of precipitation appears in mountain area while increace in oases and desert area is not obvious. Annual average air temperature increases. The rising teand is significant in oases and desert, but not in mountain area. From 1990 to 2010, the cultivated area in the Tarim Basin increase continuouslywith an increase of approximately 7200 square kilometers, of which 90% occurs during 1995 to 2005, and the increasing rate of cultivated areais faster than any other land use types. The amount of cultivated area transforming in from other land use types( mainly natural vegetation and unused land),is much larger than tha t of cultivated area transforming out, resultingin the fast increace of cultivated area, which is most obvious in Hoton, Aksu, Yarkant, and Kaidu-Kongqi, the so-called "four sourceriver basins".(2)During the 4 five-year periods from 1990 to 2010, the average annual evapotranspiration(ET)of the Tarim River Basin continues to increase, and the increase amount of 4 periods is seperately 3.2mm, 22.9mm, 14.2mm, 10.9mm every 5 years. The contribution rate of irrigated land change to ET increase in the 4 five-year periods is +1.9%, +15.7%, +21.1%, +159.8%, meanwhile the contributation rate of annual precipitation change is +98.1%, +84.3%, +78.9%,-59.8%, respectively. Land use changes resulting from h uman activities, which is mainly irrigatedland change, and climate change are two main factors that lead to the changes of ET, and differsin different periods. On the whole, the contribution rate of changes in irrigation area to ET change is increasing, larger than that of climate change.(3)In the nearly half a century, the warmer and humider climate increases origin runoff and available water resources in the Tarim River Basin. At the same time the rapid growth of cultivated arealeads to a substantialincrease in irrigation and water consumption, especially in the source flow area and the upper reaches of the Tarim River, which significantly influences the inflow to the Tarim River.Comaparative analysis of ET and irrigation simulations with irrigated area separately in 2000 and 2010 shows that for each additional 1 square kilometer irrigated area, irrigation water increases 790 million cubic meters and annual evapotranspiration also significantly increases. The water consumption caused by irrigation expansion is larger than the amount of origin runoff incease, which leads to the inflow to the Tarim River not increasing.