Transcript Presentation

Regional Water Accounts and the
Transformation of Spatial Data
11th meeting of the London Group
(Johannesburg, 26-30 June 2007)
1
Outline
•
•
•
•
•
•
Introduction
Concepts
Sources
Reallocation methods
Accuracy
Conclusion
2
Introduction
• Water accounts generally for national level and annual
• Increasing interest in regional water accounts
• River basin is internationally recognized as the unit of
reference for IWRM
• Physical water data – physical regions + water year vs
monetary data – administrative regions + financial year
• Objective: Analyze different approaches in transforming
data from one space or time boundary to another
3
Concepts (1)
• Spatial Boundaries
• Physical (continent, river basin, catchment,
aquifer)
• Administrative (country, state, municipality,
urban water authorities)
• Accounting catchment
• Temporal Boundaries
• Calendar year
• Financial year
• Water year
4
Concepts (2)
• Administrative: statistical classifications
• Physical: no statistical classification system
• Distinction foggy
• Country borders override river basins
• Aquifers vs surface water
• Accounting catchment: hybrid areas with
best possible matching
5
Sources
Compilation based on data collected for other
purposes and by multiple agencies
• Scientific measurement
• E.g. streamflow gauges, meter use: often
precisely located
• Surveys
• specific area + point in time
• Administrative data
• license registers, real estate registers etc.
6
Reallocation methods (1)
STEP 1: Assign primary spatial boundary to
accounting catchment
STEP 2: Reallocate when overlap
• Based on correlation with area, population
or other variable
• Based on correlation and additional data
• More precise location of water users
• Exclusion of certain areas
7
Reallocation methods (2)
River Basin 2
River Basin 1
Region A
Legend
River basin boundary
Administrative boundary
River
Region A
8
Common issues
•
•
•
•
Data availability
Cross-boundary activities
Confidentiality
Accuracy
9
Accuracy
• Reallocation produces errors
• Model specification error (homogeneity?)
• Example from Australia
10
Conclusions
• Temporal errors not documented
• There is a demand for regional water accounts
• Specification of accounting catchments country specific
• Existing data have to be reallocated
• Accuracy of reallocation has received little attention
• When reported, errors were large
Recommendations:
• Define accounting catchments early in the development of
accounts
• Design data collection to allow construction of regional
water accounts
11