Diachronic Climatic Impacts on Water Resources

Palinological data coming from different deposits of peat of the Spanish Central zone are presented in order to determine the climatic impact on the vegetation development, along 400 km with W-E direction, in the most western area of the mediterranean region. Given the geographic characteristics of the study area, the data coming from mountain areas (in the “Sistema Central Espanol”) and “Meseta” (“Submeseta Sur”) are compared, in order to understand the different replies of the vegetation according to the altitude, latitude and orientation, against local and global changes. Besides due to the studied period of time, special mention about the human impact manifested in the zone will be effected.

On the eve of the year 2000, humans are now facing a major environmental crisis. The atmosphere and oceans are used as dumps, forests are being logged at rates of hectares per second, natural resources are being depleted, the best agricultural top-soils are impoverished or eroded away, fish stocks are decimated and animal species are disappearing at an alarming rate. We are now witnessing the most dramatic changes to affect the earth since the dawn of civilization and it is becoming obvious that the magnitude of the stresses imposed on the earth far exceed its capacity to self-regulate, except perhaps in the context of Lovelock’s (1979) “Gaia” hypothesis. Since the industrial revolution, humans have been blindly conducting a planetary-scale natural science experiment, and only recently have they been able to foresee some of the end results of this uncontrolled experiment.

The information about the paleo-climate of the Mediterranean region is of special importance for investigating the possible impact of future climate change on the hydrological cycle. This is due to the location of this region inbetween two climatic belts: the northern zone dominated by the westerlies which bring humidty from the Atlantic ocean, and the southern area dominated by the Sahara desert belt. During winter the westerlies humid belt moves to the south, while during the summer the Sahara belt moves to the north.

The Greek landscape offers a large variety of plateau’s, lake (subsidence) basins and coastal plains which have been shaped in the course of the Quaternary i.e. the timespan of roughly the last 3 Ma. million years. It is the kind of landscape which Budel(1982) described as the “Etesian Region of the Subtropical Zone of Mixed Relief Development”. “Etesian” (from the Greek etos = year) points at the steady regularly reappearing south-bound drift of the lower atmosphere over the eastern mediterranean and adjacent lands, in the summer from mid-May through mid-September.

Climatic changes, as related to the average weather conditions experienced over a period of 30 years, have been observed in Cyprus in recent decades. This is testified to continuous reduction of recorded rainfall. The most dramatic impact of such change, relates on the insufficient output of the waterworks of the Country, as compared to that for which they were designed for. Because river flow records of only a short timespan were available at the time of the design of the waterworks, simulated flows derived from much longer rainfall records have been used instead for most catchments in Cyprus, since 1916. The mathematical models used to derive the simulated flows, from the historic rainfall, did not take climatic changes into consideration, which up to that time have not been studied in Cyprus. As such, historic high rainfall values from the beginning of the century, produced high simulated flows, which have been used for the design of the waterworks.

One of the most important features of water provision in ancient Greek cities is that as many sources of water as possible were utilized, thus reducing the reliance on any one source. That is, if the enemy cut off the aqueduct, or if an earthquake interrupted the flow of the spring, there was cistern water to fall back on. If the cistern went dry, there was the fountain. If the rains were delayed, there was still the well or the spring. This meant that the failure of anyone source had less potential to devastate the community. Use of multiple sources of water was an evolutionary advance. The survival of the community was assured by the deliberate redundency of the system.

A well-known passage in Homer’s Odyssey, probably based on an ancient ritual myth, tells the story of Demeter, the Greek corn-goddess and Iasion, the son of Zeus by Electra, daughter of Atlas. The latter was the guardian of the pillars of heaven (Odyssey, 1.53), the Titan who holds the sky up (Hesiod, Theogony, 517) and is, thereby, identified with water and rainfall.

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.

It is widely known that the atmospheric concentration of radiatively active “green-house” gases, principally carbon dioxide (CO₂), nitrous oxide (N₂O), methane (CH₄), and chlorofluorocarbons (CFCs), has increased steadily over the past century. There is considerable consensus among the international scientific community that we are facing global warming due to this growing concentration of greenhouse gases in the atmosphere. This effect is known colloquially as “the greenhouse effect”. It has been estimated that the average global temperature has increased 0.5 – 0.7 °C since the turn of the century, whereas current estimates from models indicate that a doubling of atmospheric CO₂ and other gases may increase the annual temperature by 3.0± 1.5 °C during the next 50–100 years. Such predictions are, of course, far from being certain and can, at best, be only considered as possible scenarios. Although the properties of the radiative greenhouse gases are rather well-understood, and despite the improvements in our understanding of atmospheric dynamics and large-scale climatic processes, the climatic change due to greenhouse gases is still not entirely understood, and a clear consensus has yet to emerge as to the overall direction that global climate is evolving toward.

While climate changes over periods of thousands of years are well documented, hydrologists were rather reluctant to agree for as long as a decade (1960 to 1970) as to whether changes (signals) within typical water resources systems design periods (100 years or less) can indeed be distinguished from random variations (noise) in a physical hydrological time series (US. National Academy of Sciences, 1977). The advent of general circulation models (GCMs) over the last decade and consensus about the direction of future global climate change threw abundant light on the controversial theme, thus making acceptable the aspect that climate change does exist.

About one-third of the Earth’s land surface is classified as arid to extremely arid (Fig-1), receiving insufficient precipitation to support continuous ground cover, or to permit cultivation without irrigation(Meigs, 1952). The bulk of these deserts lie between 15° and 30° North and South latitude (Fig.12-1). In these tropical and temperate deserts, precipitation primarily arrives during the summer via. monsoonal circulation. However, in western North America and central Asia, where arid lands may extend to 55° North, winter precipitation dominates. Figure 12-2 compares the temperature and precipitation regimes in the northern (winter precipitation) and southern (summer-precipitation) Great Basin.

The demand of water for consumption in Spain is 30,500 hm³ year¹. Industrial and urban consumptions amount to 1,900 and 4,300 hm³ year-¹ respectively and the rest, 24,200 hm³ year-¹ is consumed in agriculture and represents 80% of the total consumption (MOPT, 1993a). One of the main objectives of the future law on water use (“Ley del Plan Hidrologico Nacional”) is to increase use efficiency in order to increase water availability (MOPT, 1993b, pp. 22). The goal is to economize at least 1,000 hm³ year¹, that represents 4% of the volume of water currently consumed in agriculture. The specific water savings projected programs deal mainly with improvement of the irrigation systems and with an efficient adjustment between crop water demand and supply (MOPT, 1993a).

“The population of the world at mid-century was 2.5 billion; some time in 1987 it passed five billion. The increase in the past 40 years has equaled the total increase over the millions of years from when the human species emerged until 1950” (Keyfitz, 1989). This fact places in perspective the urgency for mankind’s attention to the changes occurring around us and, either directly or indirectly, effecting our collective lives. The magnitude of this problem and changes due to it will tend to overprint problems of a local to regional nature. Added to this is the potential for both natural and anthropogenic-induced climate change. Although a multitude of social, economic and environmental problems can, and are, resulting from our exploding population, and vary depending on whether we inhabit a developed or a developing nation, one irreplaceable need is common to us all: freshwater.

Of considerable concern is the increase in atmospheric CO₂ in recent years due to its influence on global climate. The studies so far have concentrated primarily on precipitation and air temperature changes from an assumed doubling in CO₂ (the 2×CO₂ scenario). For water resources, more specifically, climatic changes affect both quantity and quality. The effects on water quantity are presented in detail elsewhere in this volume and are not discussed here. The same applies also to other indirect substantial effects like changes in coastline, wetlands, etc., caused by sea level changes, flooding or erosion from coastal runoffs (Stakhiv et al., 1991).

The Mediterranean islands are especially prone to suffer droughts because of the natural climate variability (Fontanals, 1984). The relatively scarce surface and the impossibility to catch resources from distant basins, make this environment sensible to water deficits. With a surface of 3,623 km², the island of Majorca is one of the biggest in the Mediterranean sea. It has some 300 km of coastline and a mild climate, with sunshine quite every day. Majorca is a main tourism destination for all Europeans. Unfortunately, the island has no surface water resources, with irregular rains (Figs. 16.1 and 16.2), and a highly pervious soil, which implies the necessity to obtain resources from groundwater.