Water scarcity and droughts

Transcription

1 HYDROLOGY Water scarcity and droughts Antonino Cancelliere Department of Civil and Environmental Engineering University of Catania, Italy Introduction The presentation of IPCC Reports on climatic change has given new voice to concerns on the priority to be assigned to the adaptations to climatic change for avoiding dramatic water crises affecting a large part of the world population. At European level (WSDEN, 2007) a distinction is generally accepted between: PERMANENT WATER SCARCITY PROBLEMS TEMPORARY WATER SHORTAGES Unbalance between available water resources and increased demands mainly due to: population increase urbanization and tourism growth irrigated agriculture enlargement Mainly due to the natural stochastic variability of hydrological variables often worsened by inefficient water management : DROUGHT 1

2 Water scarcity Includes natural as well as man induced phenomena Natural Anthropic Permanent ARIDITY WATER STRESS DESERTIFICATION Temporary DROUGHT WATER SHORTAGE Water scarcity Average per capita available water is often used as a water scarcity indicator Commonly, 2000 m3/person/year is the threshold for water stress, 1000 for water scarcity Many countries experience less than 500 m3/person year of available water Such indicator can sometimes be misleading Renewable vs. non conventional waters Presence of irrigation Large spatial variability 2

3 Water availability Thousand m 3 /yr per capita (UNEP, 2002) Processes influencing water scarcity Natural Man induced Climatic Hydrological Climate change Water management Low average rainfall High rainfall variability Droughts Long dry seasons High temperature High evaporation Low infiltration Low soil moisture Ephimeral streamflow regime Short time runoff events Flash floods High erosion and sedimentation Low groundwater recharge Temperature rise Rainfall decrease Higher frequency of extreme events Increased flood risk Change in vegetation and land cover Increasing demands Inequity in water allocation Inappropriate irrigation practices Lack of wastewater treatment and reuse Land misuse Inadequate infrasctructures Inadequate management (Adapted from Pereira et al., 2009) 3

4 Causes of water scarcity 1. Fresh water on earth is just a small portion of the total water (~2.5%) and is distributed enevenly in time and space 2. Pro-capita availability of water is dramatically reducing due to : n Population increase n Pollution n Changes in climate According to Unesco (1996): m 3 /yr pro-capita in m 3 /yr pro-capita in 1995 (Italy 2900 m 3 /yr; Jordan 150 m 3 /yr; Malta 80 m 3 /yr) Causes of water scarcity 3. Over 20% of world population does not have access to drinking water of good quality and almost 50% does not have sanitary systems (developing countries) 4. Water costs will increase since resources more easily exploitable have already been exploited and because of the need to treat more and more polluted waters. 5. Overexploitation of surface water is causing severe damages to the fluvial ecosystems; overexploitation of acquifiers reduces both quantity and quality of groundwater. 4

5 Causes of water scarcity 6. Many countries suffer from an inefficient and ineffective water resources management. 7. Access to water is not fully recognized as an universal right of men. 5

6 Trends in water resources management Until a few decades ago: To increase available resources to supply increasing demands (hydraulics engineering) Paradigm shift: More emphasis on demand management and on a more efficient and effective management of existing water supply systems Protection of ecosystems equilibrium also to pursue social equity and heritage from one generation to another (sustainable development) Strategic proposals to fight water scarcity Ø Desalination (municipal supply) High technology Ø Increased costs Ø Difficult to apply for developing countries Ø Wastewater reuse (irrigation supply) Ø Hygenic constraints and allocation of extra costs Ø Increased efficiency in irrigation Ø Water saving Ø Water harvesting Ø Deficit irrigation Ø Virtual water trade Ø Many virtual water importers among water rich countries Ø Many countries tend to guarantee food self sufficiency Ø Use of green vs. blue water Low technology 6

7 Virtual water content in beverages Numbers are indicative and should be adjusted to local conditions (from Schreier, 2006) Drought definitions Complex phenomenon, difficult to define A comprehensive definition is difficult since it depends on: the component of hydrological cycle under investigation the time scale the way by which the deviation from the considered normal condition is measured the purpose of the analysis In general a distinction must be made between: Meteorological drought Agricultural drought Hydrological drought Water resources drought (operational) drought 7

8 Meteorological drought Drought processes and definitions Precipitation deficit Agricultural drought Unsaturated soil storage Soil moisture deficit Hydrological drought Water resource drought (operational) Surface water Groundwater storage storage Surface flow Groundwater deficit deficit Water supply systems Water supply shortage Socio-economic systems Actions to increase water availability Actions to reduce water demand Actions to mitigate drought impacts Economic, social, environmental impacts Damage Droughts 22% Earthquakes 10% Others 4% Natural disasters Floods 31% Storms 33% Affected people Droughts 35% Earthquakes Others 4% 3% Floods 34% Storms 24% Source: United Nations,

9 Drought analysis Drought is caused by anomalies (deficits) of hydrological variables and/ or water supply Anomalies: negative deviations (or departures) from normal conditions Drought indices attempts to measure and characterize in an objective and possibly standardized way such anomalies Requisites of drought indices To be representative of the type of drought of interest (meteorological, agricultural, hydrological, etc.) To enable an assessment of the severity of an historical or ongoing drought Easyness of interpretation by non-specialists Standardization, to enable comparisons in time and space To be expressed in probabilistic terms 9

10 Standardized Precipitation Index The index is based on the consideration that each component of water resources systems reacts to a deficit in precipitation over different time scales (McKee et al., 1993). Ø e.g. soil moisture is affected by precipitation anomalies in very short time; Ø while streamflow, stored volumes in reservoirs and groundwater are affected by deficit over a large time scale; The index is computed on cumulated values of precipitation over various time periods (k=3, 6, 9, 12, 24, 48 months). First a probability distribution (generally a gamma function) is fitted to the frequency curve of cumulated precipitation over k months for each individual month (e.g. January, February, etc.) Then the value of the standard normal variable corresponding to the computed probability for actual cumulated precipitation is adopted as SPI. SPI Standardized precipitation index (McKee et al, 1993) widely used for drought monitoring roughly purposes Multiple time scales Allows for comparison of droughts conditions among k different times, k Y sites ν, τ Zν, τ = k στ Standardized Precipitation Index (exact if µ SPI Z Class ΔP (%) Z 2.00 Extremely wet Z < 2.00 Very wet Z < 1.50 Moderately 9.1 wet Z < 1.00 Near normal Z < Moderately dry 9.1 k Z < Severely dry 4.4 Z<-2.00 is normally distributed) τ Extremely dry aggregated precipitation

11 SPI Index: k=12 months ANALISI DELLA SICCITA' INDICE SPI k = 12 Stazione: Acireale Quota (m s.m.): 194 Bacino idrografico: Bacini minori fra Simeto e Alcantara Precipitazione media annua (mm): 814 Distretto idrografico: 7. EST-SETTENTRIONALE d'osservazione dal : gen-1921 al: dic-2000 Periodo Versante: EST Periodo utile dei risultati dal: set-1924 al ago-2000 Mesi: SPI set-1921 set-1925 set-1929 set-1933 set-1937 set-1941 set SPI ago-1949 ago-1953 ago-1957 ago-1961 ago-1965 ago-1969 ago-1973 ago SPI set-1977 set-1981 set-1985 set-1989 set-1993 set-1997 set-2001 SPI Index: k=36 months ANALISI DELLA SICCITA' INDICE SPI k = 36 Stazione: Acireale Quota (m s.m.): 194 Bacino idrografico: Bacini minori fra Simeto e Alcantara Precipitazione media annua (mm): 814 Distretto idrografico: 7. EST-SETTENTRIONALE d'osservazione dal : gen-1921 al: dic-2000 Periodo Versante: EST Periodo utile dei risultati dal: set-1924 al ago-2000 Mesi: SPI set-1921 set-1925 set-1929 set-1933 set-1937 set-1941 set SPI ago-1949 ago-1953 ago-1957 ago-1961 ago-1965 ago-1969 ago-1973 ago SPI set-1977 set-1981 set-1985 set-1989 set-1993 set-1997 set

12 SPI index in Sicily: January 2002 SPI index in Sicily: January

13 Historical series of SPI for different k (Acireale station) SPI series in 43 precipitation stations in Sicily (k=12 months) 13

14 SPI series in 43 precipitation stations in Sicily (k=36 months) SPI series in 43 precipitation stations in Sicily (k=36 months) Piet Mondrian, Broadway Boogie Woogie,

15 Role of drought monitoring for mitigation 15

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17 Drought mitigation approach in ancient Greece Should a drought persist for a long time, and the seeds in the earth and the trees wither, then the priest of Lycaean Zeus, after praying towards the water and making the usual sacrifices, lowers an oak branch to the surface of the spring, not letting it sink deep. Pausanias, Description of Greece: book 8, chapter 38, section 4 [Arcadia] These asked for a cure for the drought, and were bidden by the Pythian priestess to go to Trophonius at Lebadeia and to discover the remedy from him. Pausanias, Description of Greece: book 9, chapter 40, section 1 [Boeotia] Current reactive approach Lack of precipitation Drought Oblivion Awareness Precipitation Panic (emergency) 17

18 Proactive approach for drought mitigation Drought mitigation measures S u p p l y increase D e m a n d reduction, water saving I m p a c t minimisation Long-term measures - New storage facilities - Water transfers and use exchange - Non-conventional resources (wastewater, desalination) - Dual municipal distribution networks - Water recycle in industries - Reduction of irrigation consumption (new crops and irrigation techniques) - Early warning system and drought contingency plan - Quality-based reallocation of water resources - Insurance and economic policies Short-term measures - Use of marginal water sources - Relaxing environmental constraints - Improvement of efficiency - Restriction on municipal uses - Restriction on annual crops - Water saving campaigns - Mandatory rationing - Temporary reallocation of resources - Public aid and tax relief - Rehabilitation programs 18

19 Drought mitigation measures Difficulties in planning a drought mitigation strategy (1/2) Inadequate understanding of natural drought phenomenon Low appreciation of a pro-active approach for coping with natural hazards Difficulty in quantifying the impacts of drought on different sectors (economy, environment, society) Strong conflicts among different groups of interest Legal and institutional constraints on the implementation of drought mitigation measures 19

20 Difficulties in planning a drought mitigation strategy (2/2) Inadequate development of tools aimed to assess the identified measures and to support the decision-making process; Lack of an early warning of water deficiency based on monitoring of hydrometeorological variables and water availability Lack of a consolidated (horizontal) coordination among water management agencies and of (vertical) communication among different decision levels. Conclusions Many countries in the world and in the Mediterranean basin in particular suffer or will suffer in the future from water scarcity, due to increasing demands and reduced available water Measures to cope with permanent water scarcity should be tailored to the particular region/country/watershed, since they have a strong impact on the local economy, social life, culture. Droughts, despite being a natural feature of every climate, yet are one of the main causes of water scarcity An effective mitigation of droughts is possible, provided an accurate monitoring and forecasting is in effect, and appropriate measures are planned in advance according to a pro-active approach 20