Mike Lee Principal Environmental Consultant GHD

Transcription

1 Revisiting the challenges posed by V Klemeš (1993) to reassess hydrological methodology in the Humid Tropics Some implications for water resource assessment Mike Lee Principal Environmental Consultant GHD

2 This presentation The late V Klemeš was a commanding figure in modern hydrology. His landmark paper The Problems of the Humid Tropics Opportunities for Reassessment of Hydrological Methodology appeared in 1993 The paper points to the profound challenges in applying many aspects of conventional hydrological methodology, mostly developed in temperate regions and based on assumptions of stationarity, to the humid tropics This presentation revisits the paper and draws out some practical implications for water resource assessment and management. This presentation provides a personal perspective and does not purport to present the views of the presenter s home organisation.

3 Vit Klemeš

4 The Problems of the Humid Tropics - Opportunities for Reassessment of Hydrological Methodology, V Klemeš Hydrology and Water Management in the Humid Tropics International Hydrology Series, UNESCO and University of Cambridge Press, 1993 Key messages The hydrology of the humid tropics is very different from temperate regions where most methodology has been developed Nonstationarity is a bigger issue past records tell us less about the future Macro-hydrological processes are more important atmosphere-ocean-land interactions are strong drivers Eco-hydrology is more important soil-vegetation-atmosphere processes are more dominant There are profound implications for water resources assessment and management

5 Nonstationarity the shrinkage of the time scale on which nonstationarity is becoming significant is presently largest in the humid tropics. The changes induced there by "modern" causes (CO2 concentrations and the long-range transport of pollutants) are happening at the same time as the drastic land-use changes. Such changes were spread over several centuries in most of the temperate zones. Klemeš (1993)

6 Nonstationarity(?) Source : National Agriculture and Climate Change Action Plan, content/uploads/2010/12/3-wa_climate- Change-observed-changes_FINAL.pdf

7 Nonstationarity(?) Inflows to Sydney's Hawkesbury-Nepean dams (excluding Shoalhaven transfers) Source: Sydney Water

8 Desalination as Insurance Major Australian Desalination Plants Plant Average production Ml/day Number of people whose water needs are met Cost (AUD) Planned wind farms for offsets MW Perth (Kwinana) m $387m Tugun (SE Queensland) 125 $1.2bn 2009 Sydney (Kurnell) m $1.9bn Adelaide (Port Stanvac) Melbourne (Wonthagi) m $1.8bn m $4bn Completion All reverse osmosis World-wide commissioned capacity (sea water and brackish) reported as Ml/day (WDR, 2009) Various public sources

9 Nonstationarity (?) Expanding retrospective view Raff, 2010 Moving window

10 Nonstationarity Flood frequency based on climate predictions, D. Raff, Proceedings of Workshop on Nonstationarity, Hydrologic Frequency Analysis and Water Management, January 2010 Boulder, Colorado

11 Designing for (Safe) Exceedance P e = 1 [1-(1/T)] n T n P e 100 year event 500 year event year event % % % % % % T Return Period N number of years P e Probability of event being exceeded over the period Probability of scoring 11 with one throw of 2 six-sided dice = 5.6% Gillespie et al,

12 Nonstationarity Many sound water management decisions can be made with surprisingly little hydrological information. The lack of knowledge can be compensated for by a corresponding increase in the robustness and resilience of the design of the relevant facilities and by maintaining flexibility of future options. In all but the simplest technological decisions, the concept of optimization is invalid because its underlying assumptions, including social, political, economic and other conditions, are changing rapidly and usually unpredictably. It is safe to say that most water management projects, however thoroughly their design may have been optimized, were far from optimal by the time they were put into operation. The return to conservative decisions with high safety margins and ample flexibility is particularly called for in the environmental context, and in regions such as the humid tropics which are undergoing rapid change. Klemeš (1993)

13 Macro-hydrology In the humid tropics, the overall control of hydrological processes by the global atmospheric and ocean circulation is more direct than in other regions - - The dynamic features originating in the tropics operate on large spatial scales and on a wide spectrum of time - - This stresses the need for analyzing the hydrological conditions and their changes in a broad atmosphere ocean-land context. Such an approach also forces an explicit recognition of the fact that the key to understanding hydrological phenomena lies outside hydrology, certainly outside the domain of the classical hydrology - in the narrow sense of the word. Klemeš (1993)

14 Macro-hydrology macro-hydrological analyses will not be feasible without a qualitatively different database than the one provided by the classical networks of sparse point measurements which hinge on local accessibility and availability of qualified personnel. The new database will have to comprise "hydrological fields", i.e., time series of areal distributions of various hydrological and related variables. Such a database is only now coming within reach through the newest remote sensing and data transmission technologies. Klemeš (1993)

15 Eco-hydrology Given the importance of vegetation in the hydrology of humid tropics and the rate and volume of their present deforestation, a thorough scientific understanding of the quantitative relationships within the soilvegetation-atmosphere segment of the hydrological cycle is indispensable for sound hydrological assessment and prediction This understanding also is needed for an adequate parameterization of the land surface processes in the GCMs in order to make it possible to model the present dynamics of the water and energy fluxes in the humid tropics quantitative eco-hydrology is the key to tackling - - (a) the local hydrological effects of local environmental changes, (b) the external effects of the local environmental changes and (c) the local effects of external environmental changes such as global warming, the long range transport of chemical pollutants and aerosols, etc Klemeš (1993)

16 Macro-hydrology, Eco-hydrology and Water Resource Assessment A key aim of water resource assessments is to provide estimates of water availability over a given period of time A water balance framework aims to provide a conceptual basis through which fluxes/ storages can be estimated for the purpose of water resource assessments Inputs - Outputs Change in storage = error term Water availability to meet growing demands Water balances help identify the consequences on surface water and groundwater stores of increased water extractions, and inter-basin transfers

17 Water Resource Assessment Regional water balance framework - Australian Water Resource Assessments System

18 Water Resource Assessment Australian Water Resource Assessments System Continental water balance On-ground data sparse in many areas Model-data fusion on-ground data satellite, radar biophysical models WIRADA-factsheet-catchment-continent.pdf

19 Australian Water Resource Assessment System AWRA landscape Model - CSIRO / Bureau of Meteorology macro-hydrology eco-hydrology eco-hydrology

20 Australian Water Resource Assessment System AWRA Landscape Model testing - CSIRO / Bureau of Meteorology Monthly mean streamflows Overall it is concluded that even without local catchment calibration the AWRA model provides useful estimates of catchment streamflow. Important characteristics are the apparent lack of bias and the strongly improved performance at longer time scales and larger spatial scales. On the basis of these findings, it is recommended that that the results can already be used for water accounting and assessment purposes as is.

21 Nonstationarity, Macro-hydrology and Eco-hydrology Some concluding remarks The future is likely to be increasingly data poor in terms of on-ground data and increasingly data rich in terms of remote sensing data Maintaining hydrologic networks is a problem everywhere governments have pressing competing priories - long term field data gathering requires patience and commitment in Australia state water resource agencies are struggling to maintain networks that have been in decline over recent decades In the humid tropics it is particularly difficult problems of access, very large events to measure, maintenance challenges including the effects of humidity and lack of standardisation of equipment due often to the legacy of different donor programs, institutional uncertainty and lack of resources and skilled staff (Manly and Askew, 1993) Scarce hydrographic resources will need to be focussed on specific objectives

22 Nonstationarity, Macro-hydrology and Eco-hydrology Some concluding remarks Traditionally we have sought to build long records the longer they are the more we will know about the future this proposition is increasingly doubtful The expanding retrospective view is misleading if climate change trends are occurring also it usually contains deeply imprinted signals of land use and other change that render it nonstationary and must be interpreted often with little contextual data to do so in many situations long records may be non existent Risk assessment also requires looking forward - this moves us strongly into the realm of macro-hydrology and eco-hydrology dynamic landscape process models, remote sensing of inputs, climate change scenarios to assess and manage water resources with increased confidence

23 Nonstationarity, Macro-hydrology and Eco-hydrology Some concluding remarks New advances in broad scale landscape modelling driven largely by remote sensing data show promise for water resource assessments where on-ground data is sparse The data fusion concept discussed earlier aims to maximise the value of what data is available - fusing models, remote sensing data and on-ground data These approaches need to tested in the humid tropics Sufficient field data collection needs to be directed towards calibrating model parameters and this may mean redirecting effort to different types of data (eco-hydrology) Investment is required in remote sensing data acquisition and processing and in climate change scenario development (macrohydrology)