Rehabilitation & Management Strategy for Over-Pumped Aquifers [China]
In the past 30 years, the aquifers in the semi-arid North China plain have been severely over-exploited. In some places, water tables dropped at a speed of 2 meters per year. The natural flow system, in which water is recharged from the mountains and in the plain and discharged towards the sea, has been reversed in both the lower and the shallow aquifer layers due to the formation of deep cones of depression in heavily exploited areas.
The overexploitation is primarily a consequence of the intensification of agriculture to feed a growing population. While the natural precipitation in the North China plain is sufficient to support one-grain crop per year under average rainfall conditions, the double cropping of mainly winter wheat and maize can only be sustained by the depletion of groundwater resources. The situation has been aggravated by the fact that annual precipitation has decreased by 14 percent over the last 5 decades.
The vulnerability of China to the impacts of climate change and inter-annual climate variability is high. Together with rapid economic and population growth and urbanization, long-term climatic trends have strained China’s water resources to an extent that all major river basins in the North and North-West are suffering from water shortage. The country’s water supply and agricultural production are threatened by changing the spatial and temporal distribution of precipitation connected with more frequent weather extremes such as prolonged droughts, heat waves, and floods. The overpumping decreases the amount of water stored in the aquifers and thus the ability of aquifers to serve as reservoirs for mitigating climate extremes.
While a release of irrigation water from a surface reservoir is easily controlled, extraction of groundwater is neither easily monitored nor effectively controlled by local water authorities due to a large number of wells involved (amounting to about 95 million in the whole of China). The difficulty posed by managing them is the major reason why many aquifers in dry countries are over-pumped. With new technology, the challenge of bringing these aquifers back to a sustainable extraction mode can be tackled.
In arid and semi-arid regions, reliable agricultural production is only feasible with irrigation. Groundwater as the only water resource, which is available all year round, has become more and more attractive to agricultural water users to guarantee reliable yield in agriculture. Severe over-pumping of aquifers has been common. It is estimated that 25 percent of the 800 cubic kilometers pumped annually from aquifers worldwide is unsustainable use which causes depletion of aquifers.
Aquifers can store water over years and are therefore particularly suited for mitigation of drought periods, which are expected to occur more frequently under climate change. To serve this purpose they must, however, be allowed to recover in times of above-average rainfall. Only under strict management, aquifers will be able to relieve droughts reliably. The main purpose of the project is to preserve or restore an aquifer’s capability of drought mitigation and provide insurance against expected climate extremes. It thus constitutes an adaptation measure with respect to climate variability.
China is the ideal laboratory to investigate control systems for groundwater, which in future can be transferred to other arid and semi-arid countries in the developing and transitioning world. China features the above-discussed problem in a severe form, the climatic conditions of interest in the context of many developing countries, the infrastructure, and personnel for a relatively fast implementation of the system and a still greater closeness to conditions in developing countries than Switzerland. It is, therefore, an excellent test bed for technologies and rural institutional development aiming at sustainable groundwater allocation and drought mitigation also in developing countries.
To rehabilitate the aquifer in the North China Plain, we propose a system where in the final stage all major pumping wells can only be operated by an Integrated Circuit (IC) card system carrying the quota allowed for each well. The quota are determined centrally using a surface water-groundwater model which in real time assimilates all observation data on groundwater levels, pumping rates of wells, surface water imports and meteorology. Quota will be set higher in times of drought to mitigate drought conditions and low in times of good availability of rain water and surface water flows to allow recovery. With a sufficiently high water table even consecutive drought years can be overcome.
The technical knowledge of controlling groundwater well fields in real time has been developed in Switzerland. Developing a control system in the agricultural context of China, demonstrating its functionality and then transferring it to developing and transition countries has a high potential to contribute to drought mitigation and climate adaptation world-wide.
The overall goal of the present project is to develop and apply a system for improving groundwater management on the basis of monitoring, modelling and controlling groundwater abstractions in an effort to restore the aquifers’ capability of mitigating climate variability.