Impact studies for agriculture and water supply

The climate mediated impacts of the IPCC SRES scenarios A2 (heterogeneous regionally rapidly growing world, 721 ppm CO₂, +3.9°C ) and B2 (heterogeneous world with high priorities for environmental quality, 561 ppm CO₂, +2°C) on the Chinese cereal supply was assessed by Xiong et al. (2007). The climate scenario was derived using PRECIS. The yield effects of climate change on potential wheat, maize and rice yields were simulated at a 50 x 50 km grid. The potential yield decreased between 12.4% (rice B2) and 36.4% (Maize, A2) by 2080 when the effects of higher CO₂ on photosynthesis and specific water use were disregarded. When CO₂ was included, theses particular negative effects changed to -4.9 for rice and +20.3% for maize.

The median term impact of climate change on rain fed crop yields and the water balance was explored by Tao et al. (2003). Two climatic periods 1961-1990 and 2021-2030 were compared at a 0.5 ° latitude/longitude resolution. The climate characteristics of the latter period were taken from the HADCM2 experiment, which included both greenhouse gases and aerosols. For Northern China, an increase in soil water deficits and a decrease in the rain-fed yield potential and in surface runoff was found.

Thomas (2000), who extrapolated recently established climate change trends towards 2030 and calculated subsequently the resulting change in irrigation demand for the main crop. Following his results the irrigation demand particularly in many parts of Northern China is increasing. For the previous 50 years Thomas (2000) reports a tendency of increasing accumulated soil water deficits in North and North east China.  This is confirmed by Tao et al. (2003) who found a trend toward agricultural water demands increasing, soil drying and significant changes in soil-moisture variability on the North China Plain and the Northeast China Plain.

The sensitivities of hydrology and water resources for China to global warming were also studied by Guo et al. (2002). Different GCM and RCM outputs were used. Regression and GIS techniques were combined to access the magnitude and timing of runoff and water resources conditions taking into account topography, river networks, land-use, human activities, vegetation and soil characteristics. A parameterization scheme was developed and the model parameters were estimated for each grid element. The runoffs of semi-dry basins in north China (Liaohe, Haihe, Ruanhe and Huaihe River) were small or even zero during dry season (from Oct. to May) and are very sensitive to temperature increase and rainfall decrease.

(source: Wechsung, project proposal)