Statistics of the Environment Water Statistics

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1 Statistics of the Environment Water Statistics Manual for water data collection Table1. Fresh water resources Luxembourg 29 th 30 th June 2004 Table 1 Table 1 collects information about quantitative apects regarding water resources and the main flows within a territory Core Table: Fresh Water Resources 2 Secondary tables: Table 1a_IF (Actual external inflow) Table 1a_OF (Actual otflow) 1

2 Main aim of the variables Table 1. Variables VARIABLES OF TABLE 1 OF THE JQ Final output Intermediate data Basic data To evaluate renewable water resources Total fresh water resources Internal flow Actual external inflow Precipitation Actual evapotranspiration To evalua te groundwater availability Groundwater available for annual abstraction Recharge into the aquifer Recharge minus ecological discharge To evaluate low flows Regular freshwater resources 95% of time An additional variable is Total actual outflow = Total fresh water resources (table 1) Consumptive water use (can be obtained from tables 2 and 3 of the JQ as it is expressed in the summary table ) Links between variables (I) Actual external inflow /////////// ///////// Precipitation Actual evapotranspiration Internal flow Total freshwater resources Consumptive water use Outflow into the neighbouring territories Outflow into the sea P-ET+EI=C+ONT+OS+DSto Where: P= Precipitation (1) ET= Actual Evapotranspiration (2) EI= Actual External inflow (4) C= Consumptive Water Use (35) ONT= Actual Outflow into the neighbouring territories (7) OS= Actual Outflow into the sea (6). DSto= Water Storage variation (= 0 in the long term) 2

3 Links between variables (II) Recharge Groundwater available for annual abstraction Ecological discharge Other restrictions GWAAA= R-ED-OR Where: GWAAA= Groundwater available for annual abstraction (10) R= Recharge into the aquifer (9) ED= Ecological discharge (11) OR= Other restrictions (See definition 10) Usual practices Main aim of the variables VARIABLES OF TABLE 1 OF THE JQ Final output Intermediate data Basic data To evaluate renewable water resources Total fresh water resources Internal flow Actual external inflow Precipitation Actual evapotranspiration To evalua te groundwater availability Groundwater available for annual abstraction Recharge into the aquifer Recharge minus ecological discharge To evaluate low flows Regular freshwater resources 95% of time Direct measurements Modelling Combined No avail. 3

4 Recommendations. Precipitation Data measured in raingage stations Reliable results can be obtained with a small quantity of stations. Selection methodologies have been developed by the EEA for EUROWATERNET Meteorological network in Spain (about stations) Stations eventually selected (100 stations) Selection methodogies in EUROWATERNET (EEA) 4

5 Precipitation map obtained from the data of all the meteorological stations in Spain Source: Spanish White paper in Water (Series ) Precipitation map obtained from the selected stations (Series ) Recommendations. Actual Evapotranspiration Lysimeters Simple algorithms (Budiko, 1974). In an average year: E = P IF Classical equations: Thornwaite, Penmann, Blaney-Criddle... (some for PET) Remote sensing (European Energy and Water Balance Monitoring System, 2000) 5

6 Actual evapotranspiration (mm) Source: EWBMS, 2001 Hydrological years: 1993/1994 (top) 1994/1995 (middle) 1995/1996 (botton) Internal flow and pristine conditions Demand area A A (Internal flow) can be only measured knowing C and B. If C and/or unavailable, mathematical modelling will be necessary. B C Gauging stat. D D=A B+C 6

7 Recommendations. Internal flow Mathematical modelling: Simple algorithms (EUROSTAT, 1998) Detailed modelling of the Hydrological Cycle Measured data: Reliable results can be obtained with a small quantity of stations. Selection methodologies have been developed by the EEA for EUROWATERNET Recommendations. Internal flow. Simple algorithms Internal flow is depending of a simple expression that links precipitation and potential evapotranspiration. Methodology used in Water in Europe. EUROSTAT. European Communities. Luxembourg.1998 (as internal renewable resources). Scale: 10 km x 10 km grid 7

8 Recommendations. Internal flow. Detailed modelling Different algorithms for each component of the Hydrological Cycle. Example: Methodology used in White Paper on Water in Spain. Ministerio de Medio Ambiente. Madrid.2000 Scale: 1 km x 1 km grid 8

9 Distributed map of Internal flow in Spain ( ) 9

10 Recommendations. Internal flow Measured data: Reliable results can be obtained with a small quantity of stations. Selection methodologies have been developed by the EEA for EUROWATERNET 28 gauging stations selected Distributed map of internal flow in Spain ( ) 10

11 Recommendations. Groundwater available Three steps: Recharge = R (estimated or measured through aquifers levels). Ecological Discharge = Ed (no methodologies generally valid for all countries) Economical and Technical restrictions = Res GAAA = R - Ed - Res Recommendations. Groundwater available Problems: Lack of methodologies and case by case studies for every water system. Total values in a country by adding. But...concept of special relevance (FWD) 11

12 Recommendations. Regular freshwater resources 95% time Portion of the total freshwater that can be depended on for annual water development during 19 of 20 consecutive years or at least 95 per cent of the years included in longer consecutive periods. One point of the resources duration curve that plots the empirical cumulative frequency of freshwater as a function of the percentage of time that they are equalled or exceeded. 95% of surface runoff over time is essentially base flows. Variable Precipitation Actual evapotranspiration Internal flow Actual external inflow and actual outflow Total freshwater resurces Groundwater available Regular fresh - water resources 95% of time Recommended monitoring/evaluation Direct measures in rain gauges. Mathematical modelling generally allows the estimation of potential evapotranspiration (PET): Actual evapotranspiration (ET) can be evaluated through curves that link the relationship between ET and PET and the available soil moisture Hydrological modelling (Ranging from simple algorithms to the detailed simulation of the Hydrological cycle) Direct measures in gauging stations located in territorial borders or in the mouth of the rivers Internal flow plus actual external inflow Steps: 1. Evaluation of recharge by moni toring of rainfall and va - riations of water table (or hyd. Modelling). 2. Evaluation of ecological flows. 3. Definition of economical o r technical restrictions Groundwater available = (1) (2+3) Statistical analysis of freshwater resources Aggregation Calculation of areal values from control points. Calculation of runoff (mm) that can be spatially aggregated for any territory. Adding of river values. All main rivers must be considered. Groundwater available has to be estimated for every water system. Total value for a country by adding the obtained values. Notes EUROWATERNET of the European Environment Agency proposes a specific methodology for selecting contr ol points to avoid understimation of the rainfall due to an uneven raingages distribution in altitude. Internal flow and actual evapo - transpiration are linked in the following simple formula: Actual evapotranspiration = (Precipitation) - (Internal flo w) EUROWATERNET of the European Environment Agency p roposes a specific methodology for selecting control points and using monitoring values in gauging stations located in non disturbed (from a quantitative point of view) rivers. For ungauged sites, flow can be estimated supposing a represen - tative runoff and weighting with the catchment area s proportion. There is not a generally accepted criterion to obtain the ecological flow. Similar to the classical analysis made for the so called flow duration curves Summary 12