Yang Dawen

Long-term variability of the carbon balance in a large irrigated area along the lower Yellow River from 1984 to 2006

The irrigated areas in the northern region of China are important food production areas. Therefore, studies on the variability of the carbon balance in these agro-ecosystems are fundamental for the management of carbon sequestration. This paper simulated the long-term variability of the carbon balance in a typical irrigated area along the lower Yellow River from 1984 to 2006, using a process-based ecosystem model called the Simple Biosphere Model, version 2. The mean annual gross primary production (GPP), mean annual net assimilation rate (NAR), mean annual soil respiration (Rs), and mean annual net ecosystem exchange (NEE) were 1733, 1642, 1304, and −338 g C m−2 a−1, respectively. A significant increasing trend in the seasonal total NAR during the wheat growing season, and a significant decreasing trend in the seasonal total NAR during the maize growing season were detected. However, no significant trend was found in the annual NAR, Rs, and NEE. The average carbon sequestration was 1.93 Tg C a−1 when the grain harvest was not taken into account, and the carbon sequestration amount during the maize season was higher than that during the wheat season. However, the agro-ecosystem was a weak carbon source with a value of 0.23 Tg C a−1, when the carbon in the grain was assumed emitted into the atmosphere.

Attribution analysis for runoff decline in Yellow River Basin during past fifty years based on Budyko hypothesis

Here 38 sub-catchments in Yellow River Basin have been selected to explore the driving factors for runoff decline in this region. Climate elasticity and landscape elasticity which indicate the sensitivity of runoff to climate and landscape change are calculated based on the catchment water-energy balance equation. Furthermore, we quantify the effect of climate and landscape change on mean annual water yield. Results show that the distribution of climate elasticity is consistent with landscape elasticity and regions with highest sensitivity is located in the Loess Plateau. The annual runoff had statistically negative trends in most study sub-catchments. Landscape change is the dominant forcing factor for runoff decline in most study sub-catchments, specially in the Loess Plateau. By the analysis of NDVI (Normalized Difference Vegetation Index) during recent thirty years, we find that the improvement of vegetation is the dominant changes in landscape. This research indicates that it is a effective and promising application approach to quantify the effect of climate and landscape change on annual water yield based on the catchment water-energy balance equation.