Effects of multiple environment stresses on evapotranspiration and runoff over eastern China

Little is known about how the terrestrial hydrological cycle responds to multiple environmental changes at large spatial scale and over long time period. Here, we applied a well calibrated and verified ecosystem model (the Dynamic Land Ecosystem Model, DLEM), in conjunction with newly developed data sets of multiple environmental factors including land use change, climate variability, elevated atmospheric carbon dioxide (CO ₂), nitrogen deposition, ozone pollution, and nitrogen fertilizer application, to characterize the spatial and temporal patterns of evapotranspiration (ET) and runoff in eastern China during 1961-2005 and further quantified the relative contributions of multiple environmental factors to these patterns at both basin and regional scales. The simulation results indicated that annual ET in the study area had a significantly increasing trend from 1961 to 2005. Yet there were no significant changing trends for estimated runoff and net water balance (precipitation minus ET). Substantial spatial heterogeneities in ET and runoff were observed. Annual ET increased in all basins except Yellow River Basin. Runoff increased in the southern part of the study area (including Pearl River and the Southeast basin), but decreased in northern part of the study area, particularly in Haihe and Huaihe river basins. Factorial analysis showed that climate change was the dominant factor responsible for the interannual variations in ET and runoff in the past 45years. Land use change (including land conversions and land management practices) yielded minor effects on the interannual variations in ET and runoff but caused relatively large effects over long-term period. For the accumulated change in ET at basin scale, climate change was the dominant factor in the basins of Song-Liao, Pearl River, while land use change contributed the most in the basin of Haihe, Huaihe, and Yellow River. Climate change was the dominant factor controlling runoff change in all basins except Huaihe and Yangtze River basins. Our simulated results imply that it is important to quantify relative roles of natural and anthropogenic disturbances on water fluxes for maintaining water sustainability in a changing climate.