GROUNDWATER DEPLETION IN THE NORTH CHINA PLAIN:THE AGROHYDROLOGICAL PERSPECTIVE

Agricultural production in the North China Plain with rainfall of less than500 mm·yr^(-1)has been steadily increasing over the past 40 years,with the groundwater levels decreasing at a rate of over 1 m·yr^(-1).In this paper,it is demonstrated theoretically that the water level in the aquifer can be expressed as a function of agricultural production and the sum of water added as rainfall and imported from outside the basin.Therefore,the most effective measures to halt groundwater depletion are importing water,decreasing cropping intensity and growing less thirsty crops.Irrigation improvements,mulching and agronomic measures that could increase the yield per unit area have less of an impact on solving the declining groundwater levels.

Responses of groundwater system to water development in northern China

The increased demands on water resources in northern China have had a significant impact on groundwater systems in the last three to four decades, including reductions in groundwater recharge capacity and overall water quality. These changes limit the potential for groundwater uses in this area. This paper discusses the issues surrounding groundwater system use in the eight basins of northern China as water resources have been developed. The results demonstrate that the recharge zone has shifted from the piedmont to the agricultural area, and that the total recharge rate in the basins tended to decrease. This decrease in arid inland basins was mainly caused by both the excessive use of water in the watershed area and irrigated channel anti-seepage. In semi-arid basins, the decrease observed in the groundwater recharge rate is related to an overall reduction in precipitation and increasing river impoundment. In addition, intensive exploitation of groundwater resources has resulted in disturbances to the groundwater flow regime in arid and semi-arid inland basins. Arid inland basins demonstrated fast falling groundwater levels in the piedmont plains resulting in declines of spring flow rates and movement of spring sites to lower locations. In the semi-arid basins, i.e. the North China Plain and the Song-nen Plain, groundwater depression cones developed and intersected regional groundwater flow. The semi-arid basins of the North China Plain and the Song-nen Plain have experienced significant hydrochemical evolution of groundwater characterized by changing water type including increase of TDS and pollutants.

Responses of phreatophyte transpiration to falling water table in hyper-arid and arid regions,Northwest China

Quantitative assessment of the impact of groundwater depletion on phreatophytes in(hyper-)arid regions is key to sustainable groundwater management.However,a parsimonious model for predicting the response of phreatophytes to a decrease of the water table is lacking.A variable saturated flow model,HYDRUS-1D,was used to numerically assess the influences of depth to the water table(DWT)and mean annual precipitation(MAP)on transpiration of groundwater-dependent vegetation in(hyper-)arid regions of northwest China.An exponential relationship is found for the normalized transpiration(a ratio of transpiration at a certain DWT to transpiration at 1 m depth,T_(a)^(*))with increasing DWT,while a positive linear relationship is identified between T_(a)^(*)and annual precipitation.Sensitivity analysis shows that the model is insensitive to parameters,such as saturated soil hydraulic conductivity and water stress parameters,indicated by an insignificant variation(less than 20%in most cases)under±50%changes of these parameters.Based on these two relationships,a universal model has been developed to predict the response of phreatophyte transpiration to groundwater drawdown for(hyper-)arid regions using MAP only.The estimated T_(a)^(*)from the model is reasonable by comparing with published measured values.

Coping with water scarcity in Kashafroud G-WADI Basin, Iran: climate change or growing demands?

This paper assesses the various factors contributing to climate change in the region of the Kashaffoud G-WADI Basin in Iron; quanti- fies the local impacts of climate change, especially local water scarcity; and simulates and discusses several proposed methods to combat these impacts. Hydrologic and climatic data are statistically analyzed and VENSIM modeling is used for various simulations of water resources in the basin. Results show that the natural climate changes affecting Kashafroud Basin include increased tempera- ture, less rainfall, more frequent droughts, and changes in rainfall patterns, all of which are local symptoms of climate change in recent years. However, the most important challenge in the basin is the overexploitation of surface and groundwater resources to meet the growing water demands, especially domestic needs. Changes in land use, reallocation of water uses, groundwater depletion, and deg- radation of the quality of surface waters have all contributed to significant changes in the environmental features of this basin, and are the main reason why water demands now exceed the renewal capacity of the basin. Proposed response measures include reallocation of resources among different uses, inter-basin water ~ansfers, drawing water from six small dams on the Kashafroud River, reducing groundwater extraction, and replacing groundwater extraction for agriculture by reuse of urban wastewater. This study concludes that although changes in global climatic pararneters have altered environmental features in the basin, local factors, such as water utilization beyond the renewable capacity of the basin, are more significant in worsening the impacts of climate change.