Grassland degradation in Northern Tibet based on remote sensing data

This study selected vegetation cover as the main evaluation index, calculated the grassland degradation index （GDI） and established the remote sensing monitoring and evaluation system for grassland degradation in Northern Tibet, according to the National Standard （GB19377-2003）, based on the remote sensing data such as NDVI data derived from NOAA/AVHRR with a spatial resolution of 8 km of 1981-2000, from SPOT/VGT with a spatial resolution of 1 km of 2001 and from MODIS with a spatial resolution of 0.25 km of 2002-2004 respectively in this area, in combination with the actual condition of grassland degradation. The grassland degradation processes and their responses to climate change during 1981-2004 were discussed and analyzed in this paper. The result indicated that grassland degradation in Northern Tibet is very serious, and the mean value of GDI in recent 20 years is 2.54 which belongs to the serious degradation grade. From 1981 to 2004, the GDI fluctuated distinctly with great interannual variations in the proportion of degradation degree and GDI but the general tendency turned to severe-grade during this period with the grassland degradation grade changed from light degraded to serious degraded in Northern Tibet. The extremely serious degraded and serious degraded grassland occupied 1.7% and 8.0% of the study area, the moderate and light degraded grassland accounted for 13.2% and 27.9% respectively, and un-degraded grassland occupied 49.2% of the total grassland area in 2004. The grassland degradation was serious, especially in the conjunctive area of Naqu, Biru and Jiali counties, the headstream of the Yangtze River lying in the Galadandong snow mountain and glaciers, the area along the Qinghai-Tibet highway and railway, and areas around the Tanggula and Nianqingtanggula snow mountains and glaciers. So the snow mountains and glaciers as well as their adjacent areas in Northern Tibet were sensitive to climate change and the areas along the vital communication line with frequent human activities experienced relatively serious grassland degradation.

Analyses on the climate change responses over China under SRES B2 scenario using PRECIS

The PRECIS,a regional climate model system developed at the UK Met Office Hadley Cen- tre for Climate Prediction and Research,which is nested in one-way mode within the HadAM3P,a higher-resolution version of the atmospheric com- ponent of the Hadley Centre climate model HadCM3,is employed to simulate the baseline (1961—1990) climate for evaluation of model’s capacity of simu- lating present climate and analyze the future climate change responses in the time-slice of 2071—2100 (2080s) under SRES B2 scenario over China relative to baseline average. It is indicated from the com- parison of the simulated baseline climate with in situ observation that PRECIS can simulate the local dis- tribution characteristics of surface air temperature over China quite well; generally speaking,the simu- lation for precipitation in the north of China and in winter is better than in the south of China and in summer,respectively; the simulation of precipitation in summer is sensitive to topography,and the simu- lated precipitation values are lower than observations over southeast coastal areas. It is shown from the analyses on the simulated climate change responses in 2080s under SRES B2 scenario relative to base- line that there would be an obvious surface air tem- perature increase in the north of China relative to that in the south of China,and especially in Northwest China and Northeast China,the amplitude ofsummer mean surface air temperature increments could reach 5℃; there would be an overall increase of the simulated precipitation in 2080s under SRES B2 scenario over most areas of China,while there would be significant precipitation decreases in South China in winter; there would be obvious precipitation decreases in Northeast China and North China in summer with high surface air temperature increase. However,it presents an obvious precipitation in- crease over the middle and lower reaches of the Yangtze River in summer.

Uncertainties in assessing the effect of climate change on agriculture using model simulation and uncertainty processing methods

Model simulation is an important way to study the effects of climate change on agriculture.Such assessment is subject to a range of uncertainties because of either incomplete knowledge or model technical uncertainties,impeding effective decision-making to climate change.On the basis of uncertainties in the impact assessment at different levels,this article systematically summarizes the sources and propagation of uncertainty in the assessment of the effect of climate change on agriculture in terms of the climate projection,the assessment process,and the crop models linking to climate models.Meanwhile,techniques and methods focusing on different levels and sources of uncertainty and uncertainty propagation are introduced,and shortcomings and insufficiencies in uncertainty processing are pointed out.Finally,in terms of how to accurately assess the effect of climate change on agriculture,improvements to further decrease potential uncertainty are suggested.

Northward-shift of temperature zones in China＇s eco-geographical study under future climate scenario

Despite the well-documented effects of global climate change on terrestrial species＇ ranges, eco-geographical regions as the regional scale of ecosystems have been poorly studied especially in China with diverse climate and ecosystems. Here we analyse the shift of temperature zones in eco-geographical study over China using projected future climate scenario. Projected climate data with high resolution during 1961-2080 were simulated using regional climate model of PRECIS. The number of days with mean daily temperature above 10℃ and the mean temperature of January are usually regarded as the principal criteria to indicate temperature zones, which are sensitive to climate change. Shifts due to future climate change were calculated by comparing the latitude of grid cells for the future borderline of one temperature zone with that for baseline period （1961-1990）. Results indicated that the ranges of Tropical, Subtropical, Warm Temperate and Plateau Temperate Zones would be enlarged and the ranges of Cold Temperate, Temperate and Plateau Sub-cold Zones would be reduced. Cold Temperate Zone would probably disappear at late this century. North bor- derlines of temperature zones would shift northward under projected future climate change, especially in East China. Farthest shifts of the north boundaries of Plateau Temperate, Subtropical and Warm Temperate Zones would be 3.1°, 5.3° and 6.6° latitude respectively. Moreover, northward shift would be more notably in northern China as future temperature increased.