World Meteorological OrganizationCOMMISSION FOR HYDROLOGYFifteenth SessionRome, Italy, 7 to 13 December 2016

CHy-15/Doc. 4.3Submitted by:

United Kingdom of Great Britain and Northern Ireland

11.XI.2016DRAFT 1

AGENDA ITEM 4: SUPPORTING THE NATIONAL HYDROLOGICAL SERVICES VALUE CHAIN

AGENDA ITEM 4.3 PROPOSAL TO DEVELOP A PILOT WMO GLOBAL HYDROLOGICAL STATUS AND OUTLOOK SYSTEM

SUMMARY

DECISIONS/ACTIONS REQUIRED:

Request CHy to consider the proposal to develop a pilot WMO global hydrological status and outlook system.

CONTENT OF DOCUMENT:

The Table of Contents is available only electronically as a Document Map*.DRAFT TEXT TO BE INCLUDED IN THE GENERAL SUMMARY

* On a PC, in MS Word 2010 go to “View” and tick the “Navigation Pane” checkbox in the “Show” section. In MS Word 2007 or 2003, go to “View” > “Document Map”. On a Mac, go to “View” > “Navigation Pane” and select “Document Map” in the drop-down list on the left.

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4.3 PROPOSAL TO DEVELOP A PILOT WMO GLOBAL HYDROLOGICAL STATUS AND OUTLOOK SYSTEM

4.3.1 The Commission considered with interest the proposal presented by the United Kingdom of Great Britain and Northern Ireland and decided …

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BACKGROUND INFORMATIONNOT TO BE INCLUDED IN THE SESSION REPORT

PROPOSAL TO DEVELOP A PILOT WMO GLOBAL HYDROLOGICAL STATUS AND OUTLOOK SYSTEM

Summary

1. This document introduces a proposed new initiative which will be considered by the WMO Commission for Hydrology at its fifteenth session. The initiative would aim to provide an operational WMO system capable of assessing the current hydrological status and its likely near-future outlook for all areas of the globe. The system would be a collaboration between NHMSs and incorporate a range of different driving data, scientific approaches and technological capabilities. It would directly build on other current WMO initiatives and existing capabilities to deliver a unique operational system providing up-to-date hydrological information from NHMSs to a range of end-users. CHy-15 will be invited to consider establishing an Expert Team (overseen by the Advisory Working Group) to scope the opportunities and challenges involved in developing such a system through an initial pilot phase. It is proposed that between 2016 and 2020 the Expert Team develop an operational and governance framework for such a global system and put in place a number of proof-of-concept pilot projects aimed at implementing into practice the underlying science and demonstrating the technological capability.

The challenge

2. Globally hydrological variability poses one of the greatest threats to the world's population. There are an increasing number of people at risk from water-related hazards and rapidly growing demands on water resources. However, there is currently no global system which is capable of assessing the current status of surface and groundwater systems or predicting how they will change in the immediate future. When the general public or the media ask the seemingly simple questions like, "How much water is there in rivers around the world at the moment?", "Is the current situation normal?" the WMO hydrological community cannot adequately respond. When aid agencies or politicians ask, "How might the global flood/drought situation change in the coming month?" we can draw on information from the meteorological community but as hydrologists we don't currently have the answers. The challenge for the WMO community is, therefore, to harness new technologies and link up other initiatives to enable us to better answer these questions. In doing so we will provide the crucial global scale information needed to help citizens understand the current status of the world's freshwater systems and adapt in light of the near-future outlook.

The ambition

3. The long-term aim of this initiative would be to develop a worldwide operational system at monthly timescales capable of providing:

(a) An indication of the current global hydrological status (including: groundwater, river flow, soil moisture);

(b) An appraisal of where this status is significantly different from ‘normal’ (for example, indicating drought and flood situations);

(c) An assessment of where this is likely to get worse over coming weeks and months.

4. Such a system is not currently available and would provide unique information of wide stakeholder relevance. The system would be delivered by NHMSs working together and offer simple, easily accessible hydrological information to users such as: government bodies (including those responsible for disaster risk reduction and water management); regional/ international aid agencies; the general public and others. The system's products would be global but capable of regional and national downscaling/application.

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Background

5. Across the globe a number of NMHSs are providing publically accessible reports of the current hydrological situation in their countries. Examples include the United Kingdom's Hydrological Summary, the United States' Water Watch and the Australian Monthly Water Update. In recent years, a number of Services have augmented such information on the current conditions with forward looking analysis of the likely hydrological conditions over a one to three month timespan, for example, the Australian Seasonal Streamflow Forecasts and the UK Hydrological Outlook. There is currently however no shared capability amongst NMHSs to assess the current hydrological conditions or outlook at an international scale through provision of global products which can be downscaled to regional/sub-regional level.

The opportunity

6. Recent years have seen significant progression in the underpinning science and national capabilities needed for such as system. Coupled with this, a number of recent international initiatives, both under the auspices of WMO and more widely, mean that there is now a clear opportunity to investigate a potential global hydrological status and outlook system.

7. In relation to the assessment of current hydrological conditions, the hydrological community has previously suffered from a lack of tools and systems to share the observational water data which would be needed. However recent initiatives looking at advancing the technological side of hydrological data sharing, include the work being done around the development of WaterML 2.0, now provide a solid basis for the communication of the underpinning data which would be required. Moreover, developing WMO initiatives such as the WMO Hydrological Observing System (WHOS) and other elements of the WMO Integrated Global Observing System (WIGOS) now provide an international framework for sharing such observational data. This new system could capitalize on these existing WMO monitoring and data sharing initiatives and provide an example of their application which would help strengthen engagement amongst NMHSs.

8. Recent scientific developments in hydrological modelling capabilities now mean we have the potential to better understand the hydrology of ungauged regions around the world. There are a number of academic projects in different countries which have applied various modelling approaches to assess global hydrological conditions. For example, the EU FP7 project EartH2Observe (E2O), in which a number of water resource models (global hydrology and land-surface models) run in parallel using data-assimilation of satellite data (precipitation, soil moisture) combined with reanalysis meteorological forcing, has shown good capacity to reproduce the observed hydrological status at a range of scales. However, these systems remain in the research environment.

9. There is now an opportunity for NHMSs to combine these developments in freshwater observations and modelling with meteorological data and forecasts available through other WMO initiatives, in order to develop an operational global-scale system, run by National Hydrological Services for the benefit of all.

Proposed development route

10. The suggested development route would see a pilot phase undertaken over the 2016-2020 intersessional period, followed by a wider operational rollout during CHy-16 and beyond.

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Pilot Phase 2016-2020

11. In order to better understand the challenges and opportunities involved in the development of such as system, it is proposed that an Expert Team is established for the 2016-2020 period to lead the development of the initiative over its pilot phase. The Expert Team could be drawn from Commission and OPACHE Members and its Terms of Reference and Work Programme be defined by the CHy Advisory Working Group. The Expert Team could, for example, be tasked to deliver the following over the CHy-15 period:

(a) The establishment, through linking with other WMO initiatives (such as WIGOS and in particular WHOS), of reliable and routing data streams for the priority monitoring and forecast information needed for the system;

(b) The development of multiple pilot projects which provide hydrological status and outlook assessments for demonstration regions around the world;

(c) A proposal for governance frameworks for the initiative which ensure widespread collaboration amongst NHMSs from across all WMO Regions;

(d) A proposed open network of NHMSs across the world who act as global/regional/sub-regional processing and analysis centres for the initiative (linked to the GDPFS).

12. In defining the Expert Team's Terms of Reference and Work Programme, it is suggested that the AWG could convene an open workshop in early 2017 to gather ideas on: the development route; the technical challenges and opportunities involved; and the possible suite of end products/outputs.

13. It is proposed that the initiative be led by the Commission for Hydrology (CHy) but that options for developing it as an inter-Commission activity (for example, with the Commission for Basic Systems and others) be explored during the pilot phase.

Longer-term development

14. The longer-term plans for the initiative would be dependent on the success of the pilot phase, but the scale of the ambition and complex interactions with multiple other initiatives across WMO means that the development of such a global system would likely take 10-15 years. A long-term strategy for the initiative would need to be drawn-up during the pilot phase, but it is likely that this would address four key long-term objectives for the initiative:

(a) To develop an operational collaborative system, involving a wide range of NMHSs, which applies multiple scientific approaches to produce unified WMO products;

(b) To connect with and support improvement/establishment of cross-WMO global systems to routinely generate and electronically exchange an extensive set of climatological and hydrological data;

(c) To establish an ongoing governance mechanism that drives the development of the products, particularly by engaging and mobilizing stakeholders, user communities and new resources;

(d) To support a framework in developing countries that helps upgrade climate service capacities and strategies of all vulnerable and low capacity countries to a baseline level.

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Outline technical methodology

15. The scientific and technological approaches employed in the system would need to be developed over the pilot phase, however the remainder of this document outlines a possible methodology which could form the basis of the initiative and provide some examples of the sorts of outputs which can currently be produced.

Overview

16. Numerical Weather Prediction and hydrological models are now sufficiently advanced to enable appropriate coupling for global scale application at relevant spatial and temporal resolution. Satellite products are widely available to provide information on hydrometeorological variables, as previously discussed ground-based observations are increasingly available globally through WMO initiatives. At its core therefore, the system would utilize:

(a) Local scale ground-based data such as river flow, soil moisture, lake levels and water table depths;

(b) Global scale remotely sensed satellite data such as precipitation, soil moisture, groundwater (GRACE) and snow cover/depth;

(c) Global/regional weather forecast (temperature and rainfall) models;

(d) Global hydrological (river flow, soil moisture, groundwater) models.

17. By integrating these different components the system would provide both: (a) an assessment of the current hydrological status across the globe; and (b) a forward outlook indicating how the status might change in the near-future. The following sections outline each of these two components and provide more detail on the current scientific capabilities (using examples from a recent EU project) and approach to an operative hydrological outlook system.

Assessment of the current global hydrological status

18. The scientific objectives of this component would be:

(a) To provide an indication of the global hydrological status (including: groundwater, river flow, soil moisture);

(b) To provide an indication of where this status is significantly different from 'normal' (indicating drought and flood status).

19. Using large-scale hydrological models, we can diagnose the current (3-monthly) hydrological status of river flow and soil moisture of the top 1m of the land surface (other options are possible such as shallower or deeper soil moisture) at the global scale (currently 0.5 degree resolution). It is relatively simple to downscale this to finer resolutions, although accuracy in the meteorological forcing data reduces with finer scales.

20. Instead of using one single model, we can use an ensemble approach which employs multiple models (usually a mixture of hydrological models and land surface models that include vegetation effects). The ensemble-mean always outperforms any single model and therefore it is much preferred to use a range of models. In addition, the driving data can be prone to error and an ensemble of weather products is more reliable than a single product.

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Current Capability

21. Figures 1 and 2 show the sort of output that can be produced with these global models. In these cases we are just showing the output from one model with one set of driving data, but an ensemble mean would be possible. These are displayed below for a typical Northern hemisphere winter (DJF) and summer (JJA).

Figure 1 Global seasonal top-1m soil moisture maps from JULES (one of the eartH2Observe LSMs). Top row: Northern Hemisphere winter (DJF). Bottom row: Northern Hemisphere summer (JJA). Left column: Season values for the year 2012. Right column: Season anomalies for the year 2012.

Figure 2 Global seasonal river flow maps from HTESSEL (one of the eartH2Observe LSMs). Top row: Northern Hemisphere winter (DJF). Bottom row: Northern Hemisphere summer (JJA). Left column: Season values for the year 2012. Right column: Season anomalies for the year 2012.

22. The long-term (in this case 34 years) climatological mean values of river-flow and soil moisture can be used to identify if the current/forecasted states are different from normal for

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the time of year. The ‘anomaly’ is the difference between the model output and the climatological mean for that season. The right hand anomaly maps in Figures 1 and 2, therefore show the potential flood and drought ‘hotspots’ for the period in question.

23. To put these conditions into the multi-year context, we can view the monthly time series of the region or site and see the development of the anomaly over time, relative to the climatological mean of that season. By way of example, the green boxes in Figures 1 and 2 highlighted some possible 'hotspots'. In the case of soil moisture, Figure 1 indicates the central United States as a dry region during the 2012 JJA season. For river flow, Figure 2 shows two sites where discharge anomalies indicated risks - a dry risk for the Congo River at a location near Mbandanka, DRC, and a wet risk for the Sao Francisco River at a location near Petronila, Brazil. The multi-year context time series for these 'hotspots' are shown in Figures 3 and 4.

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Figure 3 Top-1m soil moisture anomalies for the year 2012 (as monthly means of the year minus monthly climatology for 1979-2012) over the region highlighted in Figure 1 (Central US). Colour lines are for the range of eartH2Observe models and the black line is their ensemble mean. Dash black line represents the 2012 anomalies in the satellite derived dataset ESA-CCI for soil moisture.

Figure 4 River flow during for the period Feb 2011-Feb 2012 (continuous line) compared to climatology from the period 1979-2012 (dashed line), for the 2 sites highlighted in Figure 2. Data from the HTESSEL model that includes river routing.

24. From Figure 3 the dry anomaly in the United States for 2012 is confirmed, as all models available and also the satellite observed dataset present negative anomalies of around 4% top-1m soil moisture. For river flow, the 2011/12 DJF anomalies at the two sites are also visible in time series (Figure 5). The wet anomaly “predicted” by the model at the Brazil site is stronger, with flow more than twice higher than normal in January 2012.

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25. Finally, we can assess how unusual the conditions observed for each region/site are in relation to the inter-annual variability. Figures 5 and 6 show the annual seasonal mean values for the hotspots identified over the last 30 years. The dry summer 2012 in central US is indeed significant, as it reaches low values that had not been reached since 1988. For the river flow, on the other hand, we can see in Figure 6 that the dry anomaly in the Congo River is not very significant, but the wet anomaly in the Sao Francisco River can bring a strong flood risk, with river flow values of 8000 m3/s above normal not seen since 1992.

Figure 5 Top-1m soil moisture anomalies for the JJA season (as seasonal means of the year minus seasonal climatology for 1980-2012) over the region highlighted in Figure 1 (Central US), for the period 1980-2012. Colour lines are for the range of eartH2Observe models and the black line is their ensemble mean. Dash black line represents the anomalies in the satellite derived dataset ESA-CCI for soil moisture.

Figure 6 Seasonal DJF river flow anomalies (as seasonal means of the year minus seasonal climatology for 1980-2012), during for the period 1980-202, for the 2 sites highlighted in Figure 2. Data from the HTESSEL model, which includes river routing.

Future improvements a WMO system could deliver

26. The simple analyses above were built using the global forcing data from WFD-EI. It is derived from the ECMWF global reanalysis product ERA-Interim, while the rainfall (in particular)

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has been constrained to follow the observed rainfall product GPCC. A WMO operational version of this system would explore the possibility of interfacing with the Global Data-processing and Forecasting System (GDPFS) to make use of up-to-date meteorological observations and reanalysis products from NHMSs and WMO Regional and World Metrological Centres, in the assessment of the current hydrological state and interpretation of predictions.

27. In time, it would data-assimilate the hydrological data being increasingly made available by NHMSs through WMO initiatives (for example, river flow from WHOS Phase 2) to enhance this product. The hydrological models could also be tuned with historical observed river-flow and soil moisture data from WMO global data centres (for example, river flow data from GRDC) to give a more faithful reproduction of local conditions.

Assessment of the hydrological outlook Current Capability

28. The scientific objective of this component would be to provide an assessment of where the hydrological situation is likely to get worse.

29. This forward looking outlook element of the initiative would involve extending the above ensemble modelling approaches to provide an assessment of the likely development of hydrological conditions over the coming weeks and months. This involves using a range of outputs from meteorological forecast models to produce a forecast of the weather to force the hydrological model.

Future improvements a WMO system could deliver

30. Under the proposed WMO initiative, a far greater range of outputs from global and regional forecast models (run by NHMSs, Regional and World Metrological Centres), could be used to produce a forecast of the weather to force the hydrological models in the outlook system. This way, the hydrological models will benefit from the seasonal predictions of meteorological conditions produced by a range of NHMSs and tailored to specific regions/catchments. These forecasts would be used to drive the prediction of hydrological states: soil moisture conditions, groundwater levels, river flow. With such a system, current and near future states will be operationally assessed, and put into context using climatologies and historical data (similarl to the analysis above).

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