Every summer, we face the same problem. The levels of reservoirs fall alarmingly and experts try to find solutions, such as awareness campaigns, saving measures, or the use of less common water resources, as for example desalination, treated sewage, transfers, etc.. But, what is the role of groundwater?
The American hydrology expert R. Nace coined the term “hydroschizophrenia” to describe how little attention is paid to groundwater, while surface water is used to satisfy every demand. According to the professor of External Geodynamics of the Universidad de Granada, José Javier Cruz San Julián “in Spain groundwater is forgotten, although it is a valuable resource to solve supply problems, especially in drought periods”.
Among the numerous reasons which justify this social attitude, the researcher points out that groundwater is not visible, and for this reason less obvious. “We all know how a river works, but groundwater is more difficult to understand,” he explains. Although groundwater is well known today, hydrogeology started to be studied in the Spanish universities just a few decades ago. For this reason the responsibles for the management of water did not have this information until recently.
Regularity
Society pays attention to this resource especially in drought periods. This situation is typical of the Mediterranean climate, which is characterized by very intense dry and wet cycles. Consequently, weather conditions vary considerably from one year to another, and even in the same year, from one season to another.
As the researcher explains, surface water responds quickly to this irregular distribution of precipitation, so “a reservoir full of water can empty if there is no water recharge”. However, groundwater reacts slower to this phenomenon and for this reason it works regularly, even when surface resources are exhausted.
As a solution for these problems, the researcher proposes the joint use of water resources. This is known as “alternative use” because it is more reasonable to use surface water in wet periods and groundwater in dry periods. This also generates a rock volume which can be recharged during subsequent precipitation events”.
Cruz San Julián explains that groundwater has extraordinary importance, but he warns that “it is a vulnerable and limited resource, which has to be managed correctly, because uncontrolled use of groundwater can generate serious pollution and overexploitation problems which would be difficult to correct”. The management has to provide “a joint use of surface and ground water and any other resource, and the use of the best resource in each case.»
Agrarian profitability
The great majority of groundwater withdrawal is made by the private sector, mainly for agriculture. In Spain, there are 3.5 million hectares of irrigated land, and only one million of these are irrigated with groundwater. This means a consumption of 5,000 cubic hectometres per year (hm3/year), compared to 20,000 (hm3/year) of surface water for the rest of the land. Despite this imbalance, “the productivity in both cases is of the same order of magnitude, signifying that the gross productivity per cubic meter is five times higher when the land is irrigated with groundwater”. This value is similar in Andalusia, where 600,000 hectares are irrigated with surface water and 200,000 hectares with groundwater, with a consumption of 5,000 and 1,000 (hm3/year) respectively.
As Javier Cruz explains, this higher productivity is not due to better quality of groundwater, but to its management. “A farmer has to pay for pumping, while most of the necessary investments for the exploitation of surface water are paid by the general society. Even irrigation charges can foment waste. The charges depend on the irrigated surface area instead of the volume of water consumed”. Although it is not easy to put into practice a strict control system of the volume of water used, the researcher assures that the matter still needs to be resolved, according to the principle of the European Union of total recovery of costs, which states that the user has to pay for the water based on the amount used.
Reference
Prof. Javier Cruz San Julián
Water Institute of the Universidad de Granada
Phone. 958 248 020. Mobile phone 659 039 134. Email. jjcruz@ugr.es
