Walter Dragoni

SOME CONSIDERATIONS ON CLIMATIC CHANGES, WATER RESOURCES AND WATER NEEDS IN THE ITALIAN REGION SOUTH OF 43°N

Whatever their causes might be, climatic changes inexorably affect the water cycle. Along with trends in mean values in all aspects of the weather (precipitation, temperature, evaporation, etc.), one can expect variations in the frequency of exceptional events, and also in the hydrological regime. There maybe major consequences in terms of economy and quality of life. This has often occurred in the past, and it would be strange if does not happen again in the future. Besides the climate’s natural variability, there are good reasons to think that man’s activities these last two hundred years are leading towards a considerable rise in air temperature, the well-known anthropogenic greenhouse effect. So it is important to attempt to define in advance the environmental scenarios which can reasonably be expected to take place.

Climate change, water supply and environmental problems of headwaters: The paradigmatic case of the Tiber, Savio and Marecchia rivers (Central Italy)

River headwaters, in spite of their importance for habitats and water supply, are often inadequately studied and managed. This study discusses the effects of the hydrogeological system and climatic variations on the environment of Monte Fumaiolo (Central Italy), which corresponds to the headwaters of the rivers Tiber, Savio and Marecchia. The area is a key system for supplying drinking-water and is also the habitat of amphibians such as the endemic and endangered Bombina pachypus and other amphibian species. Ongoing climate change is affecting the area: during the last 30years, five prolonged droughts have occurred, against only one in the preceding 40years. On all time-scales, there is a decrease in rainfall during the recharge period and an increase of temperature: these trends correspond to a decrease in water yield of about 12% over the last 30years. The hydrologic system of the study area is composed of one basic aquifer and a few perched aquifers feeding springs. Their resilience to drought depends on their geological setting: study of some depletion curves helped us to understand the geological setting of the various types, and two promising sites for the habitat preservation of amphibians were identified. Study results indicate new approaches to the study and management of the environment and its water supply, which could be useful in similar areas.

Water management in low permeability catchments and in times of climatic change: the case of the Nestore River (Western Central Italy)

Abstract The analysis of the historical data series for rainfall and temperature in Central Italy indicates that a slight increase in temperature is occurring in this area, accompanied by a decrease of up to 3–4 mm/year in rainfall, rather significant when compared to the local average of 600–800 mm/year of rain. The causes of these trends are still not clear so that the persistency and intensity of these climatic variations in the future cannot be defined with any certainty. Nonetheless, when considering plans for water management, it is necessary to bear in mind that the duration of warm periods in the past and the increase in greenhouse gases suggest that these trends will persist. This situation is particularly worrying in an area where the Mediterranean climate––with hot and dry summers––causes the summer discharge of rivers to be very low or even nil, especially in the catchments––very common in Central Italy––made up of low permeability flysch-type rocks, with no significant aquifers. As an exemplification of the difficulties involved in water management and of the way to try to solve them, the authors present here the case of an artificial lake used to store water for the cooling of a thermo-electric power plant. The water from the Nestore River, located in an area with low-permeability, flysch-type rocks, fills the lake. A specially set up model was calibrated to simulate the lake level changes under different climatic conditions. The model indicated that a certain portion of the basin is enough for the needs of the power plant, even with severely limiting restrictions regarding the releasing of the minimum acceptable flow into the natural channel, and in the most pessimistic hypotheses of climatic variations.

Response of Some Hydrogeological Systems in Central Italy to Climatic Variations

One of the aims of this article is to present a series of information on the overall variations of the water surplus in Central Italy over the last 3000 years. Water surplus is understood here to be the water in the hydrological balance which is available as surface runoff and aquifer recharge. The other aims of this work are to describe the present climatic trends and, on the basis of these and that which has taken place in the past, to attempt to get an idea of what is likely to occur in the near future. A schematic map of central Italy and the location of the places mentioned in following is given in Figure 9-1. The data and conclusions given in this article refer only to the area west of the Apennine chain, roughly at a latitude between 41° and 43° 30’ N: at this time the results given here cannot be considered as applicable outside this area, especially north of the Apennine water divide.

A contribution to the definition of the ongoing climate change and its impacts on the water resources: the case of Monte Fumaiolo (Central Italy)

Monte Fumaiolo plateau, located at 1407 m a.s.l. in Northern Apennines (Central Italy), has an extension of about 11 km2. Monte Fumaiolo plateau is constituted by a set of sub-horizontal sandstone formations (San Marino and Monte Fumaiolo sandstones), having a medium-high permeability; the plateau rests on top of a low permeability rock sequence. The plateau is a good aquifer, which gives origin to a large number of small springs and to a few large ones. The Tiber River, one of the largest in Italy, originates from Monte Fumaiolo. In spite of the scarcity of hydrometric data, this preliminary paper attempts to evaluate the water budget of the plateau and the impact of the ongoing climatic change. The results so far obtained indicate statistically significant decrease of the rainfall in winter (i.e. during the recharge season) and a strong increase of temperature, due to a linear gradient of +0.44 °C/decade. This caused a decrease of the total water yield of the plateau, which will continue if the detected trends should keep going.

Pumping water wells near large surface water bodies

Estimates of water coming from surface water bodies (stream or lake depletion) are particularly necessary when siting drinking water wells near rivers or lakes with poor quality water. A finite difference model was used to analyze several hydrogeological systems characterized by large surface water bodies (i.e., lakes). A sensitivity analysis of lake width on lake depletion was made. MODFLOW model simulations show that, when lake width is more than about 2000 m, lake depletion becomes independent of its width indicating that rivers behave like lakes when width exceeds 2000 m. After about 600 modelling simulations and a best-fitting procedure a new empirical formula, allowing lake depletion to be estimated, is proposed. It expresses lake depletion as a function of various hydraulic and hydrogeological parameters, such as unit inflow to the lake, lake depth, distance between well and surface water body, filter length of the well, and pumping rate. The new formula can also be applied, with even larger approximations, to the estimation of stream depletion in cases of pumping close to surface water bodies less than 2000 m wide. The formula proposed here should be useful in deciding where to locate a pumping well and the appropriate length of its screen. Key terms: Surface water bodies, Numerical modeling, Stream depletion, Lake depletion

Evidence for karstic mechanisms involved in the evolution of Moroccan hamadas

Underground tubular karst features, observed in an arid envinroment of southern Morocco, are described. On the basis of various evidences, it is suggested that such features were originated mainly by condensation water. A computation of the time necessary for their formation supports this hypothesis.