Climate, agricultural production and hydrological balance in the North China Plain

Abstract

ABSTRACT:The North China Plain (NCP) is the largest agricultural production area in China. The extensive use of groundwater for irrigation agriculture under variable climatic conditions has resulted in the rapid decline of the groundwater table especially in areas north of the Yellow River, leading to hydrological imbalance and unsustainable agricultural production. This article analyses the sustainable level of vegetation/crop water use under the NCP climate by mimicking the evapotranspiration of a natural forest ecosystem. Such a system would have a mean annual evapotranspiration ranging from 470 mm/year in the northern to 910 mm/year in the southern part of the plain, leading to a mean annual water excess (rainfall minus evapotranspiration) ranging from 21 to 124 mm/year. The natural forest ecosystem would use less water than the current wheat/maize double cropping system. To mimic the water use of the natural system, dryland farming has to be practiced, and wheat and maize crops would have a water deficit of 90-435 and 0-257 mm/year, respectively. Under average conditions, this would mean that all the areas north of the 36°N line have to abandon winter wheat production. Stopping irrigation will lead to significantly lower wheat yields (average yield 0.8 t/ha in the north to 5.2 t/ha in the south) and increased variability in wheat and maize yield both interannually and spatially. Better management practices, such as opportunity cropping (what and when to crop depending on climate and soil conditions rather than a set annual cycle), better use of climate forecast information to direct decision making, are required in order to achieve maximum return in good years while minimising cost in bad years. Analysis on rainfall and potential evapotranspiration (PET) from 1961 to 2000 shows that there has been an increasing trend in crop water deficit in the northern part, but a decreasing trend in the southern part of the plain. It remains to be further studied whether this reflects long-term climate change or only a part of the climate variability.

Towards groundwater neutral cropping systems in the Alluvial Fans of the North China Plain

“…The RMSE of simulated as compared to measured biomass, LAI, available soil water content and grain yield was 0.88 t ha −1 , 0.72, 27 mm and 0.64 t ha −1 , respectively. The obtained parameter values and resulting accuracies are consistent with other studies using APSIM for wheat and maize simulation in the NCP (Wang et al, 2008). Fig.…”

“…The Angstrom equation was used to calculate the daily global solar radiation from sunshine hours with a = 0.18 and b = 0.55. Trends in weather in the study area have previously been described (Wang et al, 2008). A small belowground net lateral inflow ( L = 16 mm/year) coming from the mountains in the west was taken into account (Zhang et al, 2009).…”

“…Groundwater extraction must be drastically reduced to conserve the aquifers, and this would inevitably cause a large drop in production in the North China Plain (Wang et al, 2008). However, continuation of overusing the groundwater now will affect future generations who would have reduced access to groundwater, possibly none.…”

“…Zero irrigation would eventually lead to increases in the groundwater table: in wet years part of the rainfall will drain below the root zone, replenishing the aquifer. However, the yield penalties of zero irrigation are very large (Wang et al, 2008). An important question is how much groundwater can be extracted annually while maintaining a neutral or slightly positive, long term downward water flux.…”

“…Such baseline quantification is essential to determine sustainable irrigation levels. Best use of such irrigation can best be assessed via simulations (Chen et al, 2010a,b;Mao et al, 2005;Wang et al, 2008).…”